listed in alphabetical order, presenter's name is in bold.
** Indicates participation in the student contest
The Relationship Between the Type of Gas Exchange System and Behavioral Energetics in Six Arachnid Orders
**Jennifer Bosco, Ken Prestwich, Brian Moskalik
College of the Holy Cross, Worcester, MA
Arachnids exhibit striking diversity with respect to respiratory systems. Book lungs derived from book gills are the apparent ancestral condition, but tracheal lungs, “insect-like” trachea and cutaneous respiration have evolved independently. In other animal groups there is a strong relationship between the mix of aerobic and anaerobic metabolism used in “non-resting” behaviors and the type of respiratory system. Animals that use gills or lungs in conjunction with blood to move respiratory gases (vertebrates) typically mix aerobic and anaerobic metabolism during behaviors. Those that use “insect-like” tracheal respiration usually are strictly aerobic and CO2 production accurately reflects the energetics of a particular behavior. By contrast, when anaerobic metabolism is significant, CO2 production is not a quantitative measure of metabolism because pH changes associated with the accumulation of anaerobic products such as lactate drives CO2 from body fluids. Thus, CO2 exchange is the sum of CO2 produced by aerobic metabolism and additional CO2 driven from tissues. Moreover, there is also a period after activity ends when CO2 production becomes abnormally low as stores are rebuilt. We found for five species in four orders (Scorpiones, Solfugidae, Thelyphonida, Amblypygi and Araneae), which rely on blood lungs and hemolymph for gas exchange, that O2; consumption and CO2 production during recovery from forced activity are consistent with significant anaerobic metabolism. Therefore, CO2 is not an accurate measure of behavioral energetics. By contrast, in one tracheal species (an opilionid), the pattern was suggestive of metabolism that was largely, if not exclusively, aerobic.
New Mexico Linyphiidae: a preliminary look at species and response to precipitation patterns
Sandra L. Brantley 1, Michael L. Draney 2, David B. Richman 3, Linda Wiener 4
1 Museum of Southwestern Biology, University of New Mexico, Albuquerque, NM
2 Dept. of Natural and Applied Sciences, University of Wisconsin–Green Bay, Green Bay, WI
3 New Mexico State University, Las Cruces, NM
4 St. John's College, Santa Fe, NM
The arid southwestern U.S. is perhaps not considered a likely place to collect linyphiids, since they are associated more commonly with wetter habitats. However, they do occur at high elevations, along rivers, and even in drier areas during years of increased precipitation. In this presentation we focus on linyphiids collected from New Mexico, a state with biomes ranging from Chihuahuan Desert to the Rocky Mountains. Our presentation is in two parts: 1) species richness and collection localities known from NM museum material, and 2) habitat and precipitation associations for species from a long-term pitfall trapping program at Bandelier National Monument in north-central NM. In collections at UNM and NMSU we have specimens from about 70 species, including some large range extensions. Most areas of the state have not been sampled comprehensively, and we expect interesting distribution patterns, given the “sky island” effect of isolated mountains in the region. At Bandelier National Monument, 14 years of data from 3 elevations (piñon-juniper 1948m, ponderosa pine 2454m, and mixed-conifer 2712m) showed most species were collected between October and April and most were associated with mixed-conifer habitat. Abundance was low in the dry early 2000’s but numbers increased greatly with wetter conditions beginning in 2005. Dominant taxa were Disembolus anguineus (piñon-juniper), and Helophora sp., Mermessus taibo and Pityohyphantes minidoka (at the higher elevations). Because of their preferences for mesic microhabitats, linyphiids are good candidates for tracking regional climate change, especially winter precipitation. Current drought and wildfires increase the need to document the state’s diversity.
Molecular and mechanical comparisons of major and minor ampullate silks from cob-web weavers (Theridiidae)
Elizabeth Brassfield 1, Matthew Collin 2, Sandra Correa1, Cheryl Hayashi 2, Amanda Lane 1, Patrick Oley 1, Peter O'Donnell 1, Mike White 1, Nadia Ayoub 1
1 Washington and Lee University, Lexington, VA
2 University of California Riverside, Riverside, CA
3 University of Massachusetts, Lowell, MA
Orb-weaving spiders and their relatives (Orbiculariae) make at least five different types of task-specific silk that are synthesized in unique abdominal glands. These proteinacious fibers are all high performing materials in terms of strength and extensibility. We compared molecular and mechanical properties for silks synthesized in the major and minor ampullate glands of three cob-web weaving species (Theridiidae). We characterized full-length sequences of minor ampullate silk encoding genes (MiSp) from the Western black widow Latrodectus hesperus and the brown widow, L. geometricus, and partial sequences for the false black widow, Steatoda grossa. We additionally characterized partial major ampullate silk encoding genes (MaSp1 and 2) from S. grossa and compared to previously published MaSp sequences. Both MiSp and MaSp contain proline and alanine rich amino acid motifs associated with elastic β-spiral and crystalline β-sheet secondary structures, respectively. However, there are substantial differences in the proportions of these motifs among species and between proteins. We additionally performed mechanical testing of minor and major ampullate silk from each species. In general, minor ampullate silk is much more extensible than major ampullate silk, whereas major ampullate silk is stronger, tougher, and stiffer. Extensive variation among species within silk type also exists. For example, black widows have the strongest measured major ampullate silk while false black widows have the weakest. Variation in protein sequence is correlated with these differences in mechanical properties.
Sustainable Grazing: Effects of high-intensity, low frequency rotational cattle grazing on spider and arthropod communities
Alan B. Cady, Tim Bankroff
Department of zoology, Miami University, Oxford OH
Various sustainable grazing techniques have been developed for different landscapes, climates, and grazers. Attempts to measure their efficacy have produced a diversity of parameters, confounding accurate comparisons. Since arthropod communities associated with different grazers and grazing regimes are poorly known, understanding endemic arthropod biodiversity and community dynamics under different pasture management schemes may provide a metric allowing discrimination and diagnosis between various grazing plans to design those most sustainable. Thus, we initiated a study of the arthropod & spider communities inhabiting pastures under a sustainable rotational grazing schedule at a site well-positioned to assess temporal changes associated with rotational grazing and to directly compare with conventional grazing. / Arthropod communities in pastureland paddocks at Polyface Farms (Swope, VA) under high-intensity, low-frequency rotational grazing, and three immediately adjacent continuously grazed pastures were sampled in 0.25-m2 areas by first suction-sampling vegetation for 1 minute. Then all vegetation was cut to ground level and searched for remaining arthropods. A second suction session sampled the exposed substrate. The substrate was subsequently hand-searched with aspirators for 15 person-minutes. The high-intensity, low-frequency grazing significantly reduced abundance of most arthropods, and overall mean taxonomic richness was decreased. Interestingly, acari and coleoptera abundances increased. Functional group analysis found that predator richness (mostly Araneae) was maintained more than other groups despite abundance declines. The arthropod community under rotational grazing had greater species diversity and evenness pre- and post-grazing than continuously-grazed pastures. Although abundances were significantly decreased, the overall proportional representations of major taxa were maintained pre-and post-grazing under rotational grazing.
Responses of burrowing wolf spiders to resource pulses: fire and rain interrupt endless sunny days in Florida scrub
James E. Carrel
Division of Biological Sciences, University of Missouri, Columbia, MO
I wish to summarize a 26-year study of population-level responses of rare burrowing wolf spiders to two resource pulses, fire and flood. Geolycosa xera archboldi and G. hubbelli co-occur in xeric shrub habitat on the Lake Wales Ridge in south-central Florida. Annually for 26 years (1987-2012) I conducted censuses of both spiders in 15 permanent plots, each 10 x 10 m, primarily to determine whether the Geolycosa species, like many native plants and vertebrates, benefit from periodic burning of scrub. Previous studies show most spiders (80-90%) survive fires because they are protected deep in their burrows. Densities of both Geolycosa increased 3-5 fold within a year after two intense wildfires (May 1989 and February 2001), but thereafter their numbers declined because gaps of open sand quickly disappeared as the scrubby matrix re-sprouted and leaf litter accumulated. Curiously, the rate of decline in spider densities after the 2001 wildfire was precipitous compared to the 1989 burn. A post-hoc analysis showed that chronic flooding caused by 1.5 m of above-normal precipitation for 4 years in a row summer of 2001, an event that happens every 50 years or so, resulted in decimation of Geolycosa populations in most plots; the effect lasted two years.
Utrastructure and functional significance of papillae on the pedipalps of camel spiders (Arachnida, Solifugae)
**Patrick Casto 1 ,2 Paula E. Cushing 2
1 Metropolitan State University of Denver, Denver, CO
2 Denver Museum of Nature and Science, Denver, CO
Arachnids in the order Solifugae, commonly called "camel spiders," are peculiar desert dwelling arachnids whose biology is poorly known. They hold their pedipalps anteriorly while moving through the environment. Their pedipalps are covered in sensory setae. Males of certain species in the families Eremobatidae, Solpugidae, and Karschiidae have setal structures called papillae on the ventral surface of their pedipalps which are hypothesized to function as mechanoreceptors and possibly chemoreceptors. We used various microscopy techniques and specimens from the family Eremobatidae to elucidate the functional significance of these aberrant structures.
Molecular evidence for pest suppression potential and dietary selectivity in an epigeal spider community in winter wheat
Eric G. Chapman, Jason M. Schmidt, Kelton D. Welch, James D. Harwood
Department of entomology, University of Kentucky, Lexington, KY
A predator's biological control potential is best understood by determining its diet breadth. Spiders have considerable pest suppression potential because they are often the most abundant group of predators in agricultural fields. We examined the feeding habits of an epigeal spider community in a winter wheat agroecosystem through PCR-based gut-content analysis, and correlated the results with prey availability. The epigeal spiders appeared to prefer Collembola over other suitable-sized prey and Collembola predation was correlated with web area. Small Diptera and Hymenoptera were also frequently encountered (Brachycera, Platygastridae), but were under-utilized in relation to their abundance. Considering their apparent rarity on the ground, aphid predation was surprisingly high and was not correlated with web size or prey availability. Out-of-web foraging was likely responsible for the levels of aphid predation recorded for at least two of the spider species. We conclude that the epigeal spider community encountered sufficient numbers of suitable prey (Collembola) to sustain their populations such that they were available to prey on pests during immigration into the crop. Our results demonstrate that these spiders are not truly polyphagous, but appear to specialize on jumping or slowly-crawling prey (Collembola and Aphididae, respectively). Given the frequency with which they prey on scarce aphids, epigeal spiders have the potential to delay possible exponential increases in aphid populations by helping (along with other predators) to suppress early-season aphid populations.
Arachnid Genomes and i5k: The 5,000 Arthropod Genome Project
Smithsonian Institution, Washington, DC
The i5K Insect and other Arthropod Genome Sequencing Initiative (http://arthropodgenomes.org/wiki/i5K) seeks to sequence 5,000 arthropod genomes in five years. The American Arachnological Society participated in the selection of arthropod genomes, resulting in commitments to sequence the genomes of Centruroides sculpturatus, Loxosceles reclusa, Parasteatoda tepidariorum, and Latrodectus hesperus. Assembling and annotating the genomes present major challenges and opportunities. Genome size is an important practical consideration, and efforts are underway to size the genome of the pseudoscorpion Cordylochernes scorpioides. I will describe the initiative overall and suggest ways that arachnologists can participate and position additional taxa for sequencing.
Mutualism or parasitism: how endosymbiotic bacteria manipulate Linyphiid spider biology
**Megan Curry, Jenifer A. White
Department of Biology, University of Kentucky, Lexington, KY
Sheet-weaving Linyphiid spiders are widely distributed, agriculturally important predators. Like the majority of insect taxa, spiders are host to a variety of maternally inherited endosymbiotic bacteria including Cardinium, Rickettsia, Wolbachia, and Spiroplasma that ensure their own transmission through the female germline either by manipulating host reproduction or conveying a facultative benefit. Depending upon selection pressures, the selfish interests of endosymbionts may be in concert or conflict with that of the host. Recent broad-taxa screening studies indicate that endosymbionts are particularly common among spiders; however, little is known about how these bacteria affect their spider hosts. To investigate the continuum of bacterial phenotypes in Linyphiid spiders, I reared two naturally-infected lines of the Linyphiid spider Mermessus fradeorum: one infected with Wolbachia and one superinfected with Wolbachia and Rickettsia. Superinfected M. fradeorum produced almost all female offspring, whereas M. fradeorum infected with only Wolbachia produced a male-biased sex ratio. The superinfected line was not parthenogenetic: mating was required for fertile eggsac production. Subsequent generations of superinfected progeny retained a strong female bias. The exact mechanism of reproductive manipulation is not yet clear, but we hypothesize that Rickettsia induces the female bias through male killing or feminization. Future chromosome observations will reveal if feminization of genetic males has occurred. The function of Wolbachia remains unclear, but curing of Wolbachia and Rickettsia will be undertaken to investigate the possibility of cytoplasmic incompatibility, as well as to evaluate the fitness costs or benefits induced by each of the symbionts.
Specificity of attraction to floral chemistry in a crab spider (Misumenoides formosipes)
Gary Dodson1, Patricia Lang2
1Department of Biology, Ball State University, Muncie, IN
2Department of Chemistry, Ball State University, Muncie, IN
As knowledge of arachnid olfactory capabilities grows, the importance of chemical cues in foraging and mating systems is becoming more apparent. Olfactory cues could be especially beneficial to cursorial and ambush spiders living in structurally complex habitats. Field and olfactometer trials demonstrated that male Misumenoides formosipes (Thomisidae) are attracted to the floral scent of Rudbeckia hirta, but not to scents from R. hirta foliage or Morus rubra foliage. These males also showed no tendency to associate with Daucus carota inflorescences despite the fact that they commonly reside on them in the field. Female M. formosipes spent more time in an olfactometer arm with the R. hirta floral scent, although they did not move towards R. hirta inflorescences as a first choice over a control. The use of phytochemical cues by males to locate R. hirta inflorescences should increase encounters with potential mates as this is the substrate on which females in our population are found with the greatest predictability.
Diversification on the Bare Hills of Granite
Roberta Engel ¹, Elizabeth Jockusch ², Mark Harvey ³
¹ Dept. of Biological Sciences, 100 Galvin Life Sciences Center, Notre Dame, IN
² University of Connecticut, Storrs, CT
³ Western Australian Museum, Perth, Australia
Thirty-four biodiversity hotspots have been recognized by Conservation International; this designation is based on two criteria, floristic richness and habitat loss. The rich arthropod heritage, including arachnid diversity, found in these regions is frequently under-assessed. Southwestern Australia is one of the global hotspots. A distinctive feature of the region is an extensive system of granite outcrops. Our research focuses on the pseudoscorpion fauna that is restricted to this terrestrial archipelago. When our work commenced, only one described species, Synsphyronus elegans, had been recorded from the outcrops and it was known only from its type locality. Currently, Synsphyronus Chamberlin (Garypidae: Pseudoscorpiones) comprises 31 described species in Australia and New Zealand. We visited over 100 outcrops in southwestern Australia during three field seasons; populations were found on two-thirds of the granite islands. Additionally, lineages were sampled in each of the four biomes in Australia; sixteen described species are included in this study. Evolutionary relationships between lineages were inferred using molecular data. Gene trees were reconstructed for four nuclear markers (elongation factor 1-alpha, actin 5C, internal transcribed spacer regions, and wingless) using multiple phylogenetic methods. Three major clades were recovered; the outcrop taxa are not monophyletic. Deep genetic divergences across small spatial scales exist between some outcrop populations. Southwestern Australia harbors a rich Synsphyronus fauna. Species level diversity on the outcrops is greater than the four presently described endemic species. Similarly, many of the non-outcrop lineages cannot be assigned to described species. Synsphyronus is a successful genus; its diversity is clearly underestimated.
Effects of immune stress on multimodal sexual signaling of Schizocosa ocreata wolf spiders
**Rachel Gilbert, Kathryn Surkarski, Rick Karp, George Uetz
Department of Biological Sciences, University of Cincinnati, Cincinnati, OH
Theory suggests that male signals and secondary sexual traits may serve as honest indicators of immune function in female mate assessment. Male Schizocosa ocreata wolf spiders exhibit multiple condition-indicating traits (foreleg tufts, courtship vigor) used as criteria in female mate choice, but the direct and/or indirect effects of immune stress on these sexual signaling traits is unknown. To evaluate the effects of immune stress on sexual signaling, immature males were infected with a bacterial pathogen (Pseudomonas aeruginosa) and were assessed at maturity for several fitness-related measures. Fluctuating asymmetry (FA) in male foreleg tufts (secondary sexual characters) was significantly greater in spiders subjected to bacterial infection. Adult mass and body condition indices were significantly lower among infected individuals than uninfected (control) individuals. In addition, we examined whether females can detect infection status via chemical cues in male silk. Females were significantly more receptive and showed more receptivity displays towards a courting male video stimulus when uninfected male silk was placed in front of the screen than infected male silk. Females also spent significantly more time on uninfected male silk than infected male silk. These results indicate that immune stress from bacterial infection significantly reduces overall body condition and negatively impacts key indicator traits (leg tufts), potentially reducing mating success. These results also show that it may be possible for females to detect infection via male silk cues. Ongoing research will investigate further the role of immune stress on sexual selection in this species.
Reproductive partitioning and task specialization in social spiders
Lena Grinsted, Trine Bilde
Institute of Bioscience, Aarhus University, Aarhus, Denmark
Reproductive partitioning is a key component of social organization in groups of cooperative organisms. In colonies of permanently social spiders of the genus Stegodyphus less than half of the females reproduce, while the rest perform suicidal allomaternal care. Theory suggests that reproductive skew is a product of contest competition within colonies, leading to size hierarchies where only the largest females become reproducers. Alternatively, reproductive skew is an adaptive strategy whereby reproduction is differentiated in order to maximize colony survival and production through inclusive fitness benefits of allomaternal care. We investigated the effect of competition on within-group body size variation over six months in Stegodyphus dumicola, by manipulating food level and colony size. We found no evidence that competition leads to increased size asymmetry within colonies, suggesting that contest competition may not be the mechanism leading to reproductive skew. Within-colony body size variation was high already in the juvenile stage, and did not increase over the course of the experiment. This is consistent with the hypothesis of adaptive reproductive skew mediated by processes shaping body size variation at an early stage, facilitating task specialization within colonies. We suggest that reproductive skew in social spiders may be an adaptation to sociality. Colony benefits would arise by ensuring that some females become reproducers while their offspring benefit from allomaternal care provided by non-reproductive helpers.
Neuroendocrine control of molting in the scorpion Heterometrus swammerdami
School of Life Sciences, Jawaharlal Nehru Univ. New Delhi, India
Neuroendocrine control of molting in scorpions is time tested from the past 430 million years. Scorpions are considered as the first air breathing and land dwelling animals on our planet earth. The scorpion brain assumes a central role in the whole process of molting. In Heterometrus swammerdami, specialized neurons in the protocerebrum synthesize the brain hormone, and communicate with the other neural organs like the subesophageal ganglion, hypocerebral ganglion, and the rostral and frontal ganglia. After receiving the neuronal and hormonal cues, the subesophageal ganglion of the scorpion is able with its own neurosecretory cells, to communicate with the functionally similar structure to that of prothoracic gland of pterygote insects. This analog - the blind end organ, in turn , transports the synthesized active biological principle, to various targeted regions of the body through the blood cells (oenocytes). These are responsible for the further development and growth of organs. Through the feedback mechanism, the brain is kept informed about the internal milieu, and the attainment of sexual maturity. The scorpion Heterometrus swammerdami undergoes periodic molting until it reaches adulthood. The structural analogs of the prothoracic gland and corpus allatum complex of insects are compared with those of scorpion in the present study. The neuroendocrine control of molting and the involvement of counterparts of ecdysone, neotenin and the feedback control mechanism in the molting phenomenon of the scorpion Heterometrus are discussed in this communication.
Ecological implications of diel rhythm in aggressiveness in Anelosimus studiosus (Araneae: Theridiidae)
Thomas C. Jones, Chelsea R. Ross, J. Colton Watts, Darrell Moore, Edith Seier & Michele L. Joyner
Department of Biological Sciences, East Tennessee State University, Johnson City, TN
Ecologically, spiders are both predators and prey. Behaviorally they must balance being bold enough to capture prey while being wary enough to avoid potential predators. However, the relative adaptiveness of boldness and wariness can change with context, such as hunger level, reproductive status, or changes associated with the daily cycle. In this study, we explore the relationship of aggressiveness to reproductive state, and observe if aggressiveness changes over the daily cycle, in the spider Anelosimus studiosus. We test the hypotheses that (A) brooding females will be more aggressive than non-brooders, and (B) that aggression level will fluctuate over the course of a day, reflecting relative abundance of prey and/or potential threats. Spiders were entrained to a 12:12 LD cycle in the lab, and we observed their responses to simulated predator attacks at four hour intervals over four days. We also monitored activity levels for four days under 12:12 LD conditions. Finally, we sampled flying insect densities in the spider’s natural habitat every three hours for two days. We found that these spiders showed robust nocturnal activity, and that females which had produced broods were more aggressive than those which had not. We also found that aggression levels of non-brooding females changed significantly over the course of a day in a pattern similar to the daily fluctuations in density of both prey and parasitoid wasps.
Contact function explains negative allometries of copulatory structures
Joseph T. Kilmer, Rafael L. Rodriguez
University of Wisconsin – Milwaukee, Milwaukee, WI
Sexual traits vary greatly in how they scale relative to body size -- i.e., their static allometry. Some traits scale proportionally with body size (isometry), while others scale more steeply (positive allometry) or more shallowly with body size (negative allometry). Genitalia present the most consistent allometric pattern among animals, showing predominantly negative allometries. This pattern may be explained by selection on genitalia through their function either as contact courtship devices or as sperm transfer devices. The contact-courtship hypothesis predicts that non-genitalic male structures that contact females during copulation will scale shallowly with body size like genitalia, while the sperm-transfer hypothesis predicts that they will not. Here we test these predictions with Leiobunum vittatum (Arachnida: Opiliones) harvestmen, in which males grip females with the tarsi of their pedipalps and certain legs during copulation. We measured these traits as well as genitalia, body size and structures not used in copulation, and we calculated their allometric slopes. We found that the tarsi of the legs and pedipalps that grasp females during copulation had distinctly shallower allometric slopes than non-contact segments of the same appendages. Furthermore, they also had shallower slopes than tarsi of non-contact legs. These results support the hypothesis that genitalia scale shallowly because of their role in contact courtship. We discuss implications for selection on the scaling of trait size relative to body size.
Hello pretarsus! A journey through the internal morphology of the distal segment of a spider leg
Facundo M. Labarque, Charles E. Griswold
California Academy of Sciences, San Francisco, CA
In the last century much research has been conducted on the comparative morphology of walking appendages among Chelicerata. A leg consists of several podomeres connected by joints. The distal podomere is the pretarsus, a plate-like structure connected to the rim of the tarsus by transverse bicondylar joints, which permits a levation-depression motion. In spiders, the pretarsus consists of a sclerotized claw lever, which sometimes bears the unpaired claw and is connected to the pair claws by a membrane and sometimes associated with two tenant plates. The pretarsal levator arises from the dorsal surface of the metatarsus and inserts on the dorsal rim of the pretarsus, whereas the pretarsal depressor arises from the dorsal surface of the metatarsus and tibia and inserts on its ventral rim. Our current knowledge of pretarsus conformation and function is well known for only one species, Phidippus audax (Salticidae). In our study, we attempt to increase this data set by examining the pretarsus of several taxa, with an emphasis on haplogyne spiders, in order to find new phylogenetic characters. Our preliminary results show that the pretarsal levator and depressor consist of two strands, and that the first continues underneath the membrane between the paired claws and inserts dorsally on the anterior face of the claw lever. The distal end of the pretarsal levator may be single or bifurcated, straight or swollen, whereas that of the depressor could be wide or tubular, and may insert underneath the claw lever or through a posterior ventral hole in it.
Massively parallel signature sequencing reveals novel genes associated with silk production in the Western black widow, Latrodectus hesperus
Amanda Kelly Lane 1, Cheryl Hayashi 2, Greg Whitworth 1, Nadia Ayoub 1
1 Washington and Lee University, Lexington, VA
2 University of California Riverside, Riverside, CA
Spiders produce task-specific fibers in unique abdominal glands, such as the dragline silk synthesized in major ampullate glands and outer egg casing silk, which originates in tubuliform glands. These fibers are composed primarily of one or more structural proteins. For instance, MaSp1 and MaSp2 constitute dragline silk, and TuSp1 forms egg casing. Our goals were to identify the relative expression of structural proteins in the major ampullate glands and to identify other potential genes involved in silk synthesis. We created libraries of 3’ anchored, 20 base pair “tags” from genes expressed in the cephalothoraxes and major ampullate glands of two adult females. We sequenced at least five million tags from each library, which resulted in 32,111 unique tags that had more than one count per million in at least two of the four libraries. In order to determine genes associated with the tags, we compiled a database of published genes (368) and generated an additional 260 sequences from a whole female black widow cDNA library. Of the 268 tags that matched a gene, 62 were significantly more abundant and 41 were significantly less abundant in major ampullate glands than in cephalothoraxes. Genes highly expressed in major ampullate glands included the structural proteins known to be in dragline silk, MaSp1 and MaSp2, as well as other structural proteins such as TuSp1. An additional 21 protein coding genes were more abundant in major ampullate glands than cephalothoraxes, representing a plethora of novel genes that are likely important for silk synthesis.
Rediscovery of Tengella perfuga and Description of the Male
Matthew Leister, Rachael Mallis
University of New Mexico, Albuquerque, NM
Tengella perfuga Dahl (1901) has remained poorly known since Dahl’s original description of two female syntypes. With the male heretofore undescribed its classification has been uncertain, and it has been sometimes placed in synonymy with the better known T. radiata (Kulczynski). With males undescribed, an unknown natural history and a vague type locality (“Sud Amerika?”) it would seem unlikely this spider would be easily rediscovered. However, recent collecting in Nicaragua resulted in discovery of T. perfuga populations with adult males, females and various life stages. Tengella radiata populations were also discovered which allowed for comparison between species. We confirm that T. perfuga is a valid species, redescribe the species, including the first description of the male, document the distribution, designate a lectotype and compare the species with T. radiata.
Natural History Notes On Dahl’s Lost Species, Tengella perfuga Dahl, and Comparison with T. radiata (Kulczynski)
Rachael Mallis, Matthew Leister
University of New Mexico, Albuquerque, NM
During a recent field trip to Nicaragua the natural history and habitat of the poorly-known Tengella perfuga Dahl was observed. Previously known only from Costa Rica, we also discovered T. radiata (Kulczynski). Here we present field and laboratory observations and comparisons of web structure and density, feeding behavior, and courtship between T. perfuga and T. radiata. Despite considerable similarity morphologically, the two species differ in their behavior and habitat preference.
Testing a Rapid Assessment Protocol for Spiders in Nantucket Sandplain Grassland and Coastal Heathland
Andrew Mckenna-Foster1, Michael L. Draney2
1Maria Mitchell Association, Nantucket, MA
2Department of Natural and Applied Sciences, University of Wisconsin-Green Bay, Green Bay, WI
We have been developing a Rapid Assessment Protocol (RAP) for spiders and other invertebrates in which randomly located 0.01 ha plots are intensively sampled within a standard 0.25 ha site, with the goal of providing richness estimates that are comparable across studies and locations. We tested this RAP in sandplain grassland and coastal heathland on Nantucket Island, Massachusetts in two different seasons (June and August) by comparing the RAP collection to a collection of spiders from the same area sampled using standard methods of pitfall trapping and plotless beat/sweep samples. The June samples comprised 124 spiders from 23 species (RAP) and 314 spiders from 58 species (Standard Methods), and the August samples comprised 414 spiders from 30 species (RAP) and 47 spiders from 24 species (Standard Methods). The June RAP found 37% of the estimated species present and added four species to the seasonal list. The August RAP captured 71% of the estimated species present and added 18 species to the seasonal list. The August collection also added three species to the species list that were not caught at any other time of the year. Both RAP tests required approximately 65% less time than the standard collections and pitfall trapping when counting time collecting, travelling, and processing. The RAP can result in a substantially similar species list from a much more rapid and efficient sampling effort, although this efficiency may be offset to some extent by a susceptibility to fluctuations in daily weather or collecting conditions.
Using PCR to reveal a spider-dominated leaf-litter food web
Robin Mores, David H. Wise
Department of Biological Sciences, University of Illinois at Chicago, Chicago, IL
The application of PCR to food-web research has the potential to greatly advance our understanding of the structure and dynamics of food webs. Using the spider-dominated leaf-litter food web as a model system, this research project utilizes Real-Time PCR to reveal the predator-prey interactions between major taxa within a forest-floor arthropod community. Our model web consists of 20 nodes. Real-Time PCR is used to examine the gut contents of ten focal predators (families of spiders) for the DNA of eight non-predacious prey taxa, two non-spider predator taxa, and the DNA of the other nine spider families. Through a combination of litter-sifting and hand-collection, over 5000 spiders have been collected from field sites located within the Palos region of the Forest Preserve District of Cook County (Chicago, IL). DNA is extracted from the gut contents of these spiders and Real-Time PCR is used to identify the prey item(s) that each spider has consumed. To date, over 6000 interactions have been examined between the 20 taxa that make up this model food web. Preliminary results demonstrate that it is possible to detect prey DNA from 12 different prey taxa, including other spiders. Based on this data, a quantitative food web has been constructed that elucidates the structure and interaction pathways within this spider-dominated arthropod community.
Are the viscous prey capture threads of araneioid orb-webs adapted to different humidity regimes?
Brent D. Opell, Shannon E. Karinshak, Mary A. Sigler
Department of Biological Sciences, Virginia Tech, Blacksburg, VA
Viscous threads that form the sticky prey capture spirals of araneoid orb-webs feature regularly spaced droplets, each comprised of a glycoprotein glue core that is covered by aqueous material and supported by axial fibers. This glycoprotein is a viscoelastic solid, whose extensibility facilitates the summation of adhesion from multiple droplets and dissipates energy of prey impact and struggle. Low molecular weight compounds in the aqueous material make the droplet hygroscopic, causing its volume to change with relative humidity (RH). As RH increases some of this absorbed water is taken up by glycoprotein, causing its extensibility to increase. We measured the features and responses of viscous droplets of two large orb-weavers, Argiope aurantia and Neoscona crucifera, at 20%, 37%, 55%, 72%, and 90% RH. Argiope aurantia droplet extension increased linearly with RH; whereas that of N. crucifera increased exponentially. The volume specific extension of A. aurantia glycoprotein reached a maximum value at 55% RH and then declined, whereas that of N. crucifera increased exponentially through the RH range. As humidity increased the stress on droplet filaments at maximum extension, as gauged by axial line deflection, decreased in A. aurantia, but increased exponentially in N. crucifera. These differences suggest that A. aurantia threads are adapted to low and intermediate RH environments, whereas N. crucifera threads are adapted to a broader RH range and may be optimized for higher RH. The hygroscopicity of a droplet’s aqueous coat appears to play a crucial role in this adaptation, perhaps complimented by changes in glycoprotein molecules.
Neurochemical Levels Correlate with Population Level Differences in Social Structure and Individual Behavior in the Polyphenic Spider, Anelosimus studiosus
**Jennifer Price 1, Thomas C. Jones 1, David S. Roane 2, Jonathan Pruitt 3, Susan Reichert4
1 East Tennessee State University, Johnson City, TN
2 Bill Gatton College of Pharmacy, East Tennessee State University, Johnson City, TN
3 University of Pittsburgh, Pittsburgh, PA
4 University of Tennessee, Knoxville, TN
Anelosimus studiosus is a socially polyphenic spider. Individuals can be classified as social/tolerant or solitary/aggressive. These behavioral differences are associated with considerable variation in social structure. Here, we begin to examine the physiological differences that may underlie the behavioral dimorphism in this species and possible implications for the evolution of sociality. Octopamine is a neurotransmitter that has been found to elevate aggression in invertebrates. Serotonin has been shown, in some cases, to interact antagonistically with octopamine. We used High Pressure Liquid Chromatography with Electrochemical Detection to quantify levels of these neurochemicals among adult females from social (multi-female) and solitary (single-female) webs in east Tennessee. A subset of spiders was scored for individual social tendency. We found that higher octopamine levels are associated with a greater degree of aggression and intolerance, both at the individual level and the population level, while higher levels of serotonin are found in multi-female colonies and social individuals.
Tarsal flexor system and sexually dimorphic tarsal glands in gonyleptoid harvestmen (Opiliones, Laniatores)
Daniel N. Proud
Department of Biology, University of Louisiana at Lafayette, Lafayette, LA
Appendicular characters such as intrinsic musculature have remained an important aspect of evaluating and explaining the hypothesized phylogenetic relationships among arachnid orders. In the present study, I examine the general tarsal morphology for laniatorid harvestmen (Opiliones) and describe a novel system of retinacular structures, termed the tarsal flexor system, which functions to maintain close apposition between the tendon and internal ventral surface of the cuticle to provide mechanical advantage for tarsal flexion and other movements of the tarsus. I discuss this system with regards to other lineages of Opiliones, especially those that exhibit prehensility of the tarsus (i.e., Eupnoi), as well as other orders of Arachnida. Additionally, I compare the sexually dimorphic tarsal glands among gonyleptoid families and discuss phylogenetic implications based on recently hypothesized relationships within this superfamily.
Iterative evolution of increased behavioral variation characterizes the transition to sociality in spiders and proves advantageous
Jonathan N. Pruitt 1, Christopher Oufiero 2, Leticia Aviles 3, Susan E. Riechert 4
1 University of Pittsburgh, Pittsburgh, PA
2 University of California, Davis, Davis, CA
3 University of British Columbia, Vancouver, BC
4 University of Tennessee, Knoxville, TN
The evolution of group living is regarded as a major evolutionary transition and is commonly met with correlated shifts in ancillary characters. We tested for associations between social tendency and a myriad of abiotic variables (e.g., temperature, precipitation) and behavioral traits (e.g., boldness, activity level, aggression) in a clade of spiders that exhibit highly variable social structures (genus Anelosimus). We found that, relative to their subsocial relatives, social species tended to exhibit reduced aggressiveness towards prey, increased fearfulness towards predators, reduced activity levels, and tended to occur in warm, wet habitats with low average wind velocities. Within-species variation in aggressiveness and boldness was also positively associated with sociality. We then assessed the functional consequences of within-species trait variation on reconstituted colonies of four test species (A. eximius, A. rupununi, A. guacamayos, A. oritoyacu). We used colonies consisting of known ratios of docile/fearful versus bold/aggressive individuals and group foraging success as a measure of colony performance. In all four test species, we found that groups composed of a mixture of docile/fearful and aggressive/bold individuals outperformed monotypic groups: (1) mixed groups were more effective at subduing medium and large sized prey, and (2) mixed groups collectively gained more mass during shared feeding events. Our results suggest that the iterative evolution of depressed aggressiveness and increased within-species behavioral variation in social spiders is advantageous, and could be an adaptation to group living that is analogous to the formation of morphological castes within the social insects.
Behavior in the spider nursery
Susan Riechert 1, Jonathan Pruitt 2, Jason Wolf 3
1 Department of Ecology and Evolutionary Biology, University of Tennessee, Knoxville, TN
2 Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA
3 Department of Biology and Biochemistry, University of Bath, Claverton Down, Bath, UK
The desert spider, Agelenopsis aperta, has been a model organism, exemplary of an aggressive syndrome. In this study, we investigated juvenile behavior during early feeding bouts that would occur while sibs are clustered in the immediate vicinity of the female parent’s web-site. We examined the behavior paired juvenile sibs exhibited during weekly feeding bouts to determine whether contest competition (competes for prey), scramble competition (attacks only prey offered to it, ignoring the other sib) or cooperation (joint capture and subsequent feeding) occurs during this period of group-living. We found significant familial variation in the nature of the behavioral interactions juveniles exhibited during the feeding bouts. Despite the fact that food levels were biased against contesting prey, contest behavior predominated and evidence of the exhibition of despotic behavior will be presented. Note, however, that injurious behavior was extremely rare and likely the result of misidentification.
Modeling encounter rates within a wolf spider communication network
J. Andrew Roberts ¹, George Uetz ², David Clark ³
¹ The Ohio State University at Newark, Newark, OH
² Department of Biological Sciences, University of Cincinnati, Cincinnati OH
³ Department of Biology, Alma College, Alma, MI
Multimodal signals have likely evolved to compensate for environmental constraints inherent to complex habitats, but animals that utilize multimodal signals experience many selection pressures that could affect the evolution of signaling behavior. The risks to senders and intended receivers are primarily related to signal exploitation by social and/or interceptive eavesdroppers. One key factor necessary for understanding the influence of unintended receivers on signal evolution is to establish a realistic estimate of interaction rates within the social, or communication, network. We explored interaction rate estimates using a common model of multimodal communication, the brush-legged wolf spider, Schizocosa ocreata (Araneae: Lycosidae). Male behavior, distance traveled, and interactions with conspecifics and heterospecifics were observed across multiple field seasons. Behavior and distance data was combined with field measurements of the active space of visual and seismic courtship, and used in modified ideal gas equations to estimate mobile active space and interaction rates for males during the peak mating season. Estimates were compared to observed interaction rates from the field to explore their utility in further studies of multimodal signal evolution.
Herbicide and predator exposure during mating have contrasting effects on egg production in the wolf spider, Pardosa milvina
Ann L. Rypstra, Laurie M. Greisinger, Samuel C. Evans
Miami University, Hamilton OH
In many ways, exposure to anthropogenic chemicals is analogous to encountering predators: sub-lethal exposure can shift the behavior or aspects of the life history of the target species. Previous work demonstrated that the wolf spider, Pardosa milvina (Araneae, Lycosidae), reduces its activity both in the presence of chemotactile cues from the larger wolf spider, Hogna helluo (Araneae, Lycosidae), and in the presence of glyphosate-based herbicide. Here we tested the hypothesis that exposure to these two stressors while mating would affect eggsac production. Virgin males and females were introduced to field enclosures that were treated with glyphosate, water, predator cues, or nothing. They were left to interact with one another for 24 hrs. and then returned to the laboratory where they were maintained until death Fewer of the females from containers with predator cues produced eggsacs and they took longer to produce eggsacs than controls. Glyphosate had no effect on the likelihood of producing eggsacs but exposed animals produced eggsacs more quickly than controls. Predator- and herbicide-stressed females produced smaller first eggsacs than did control females but subsequent eggsacs did not differ among treatments. Females that mated in the presence of herbicide produced more eggsacs in their lifetime whereas females mating with predator cues present produced fewer eggsacs than their unstressed counterparts. Hence these two common stressors have different impacts on the reproductive biology of the spider and the collective impact of predator cues seems to have greater negative consequences to reproductive output than exposure to a common herbicide.
Spatiotemporal interactions in a carnivorous plant-spider community
Jason M. Schmidt, James J. Krupa, James D. Harwood
University of Kentucky, Lexington, KY
Spatial pattern can have significant effects on interactions between species. In particular, the presence of sessile predators likely influences mobile predators with the reciprocal also a possibility. In this study, we documented the spatial distribution of sundews (Drosera brevifolia), a carnivorous plant in a wet prairie habitat in Kentucky. We used sticky traps to measure the plant's potential dietary overlap with web-building spiders and PCR-based molecular gut-content analysis to assess predation levels by the spiders. We found the highest densities of sundews in the northern portion of the plot with lower densities either in the southern portion, or where spider websites were most abundant. We observed seasonality in sundew size and distribution with the highest cover and largest sundews earlier in the season, which decreased over time and recovered later in the season. Sixteen spider species were observed, the most common being Neoantistea agilis (Araneae: Hahniidae). Prey activity-density varied seasonally, being highest in the southern area, intermediate at spider websites, and lowest in the northern area containing the highest sundew densities. We found high levels of predation by spiders on the most common prey taxon, Collembola, which was neither seasonally structured nor correlated with prey abundance. Our results indicate that the composition of prey at sundew or spider microsites is similar, but that areas with higher densities of sundews potentially reduce available prey making these sites lower quality for other predators. Further study will target understanding the effects of other environmental gradients driving the interactions in these multi-kingdom carnivorous communities.
Prey sharing and communal living in two species of African tarantula: Heterothele villosella and Hysterocrates gigas
**Sarah Schrader, Cara Shillington
Department of Biology, Eastern Michigan University, Ypsilanti, MI
Sociality is well documented in many different animal taxa including spiders, but it has rarely been explored in tarantulas. This study examined sociality in two species of African tarantula: the Cameroon Red Tarantula (Hysterocrates gigas) and the Tanzanian Dwarf Chestnut Tarantula (Heterothele villosella). In captivity, juveniles of both species have been documented sharing prey items or cluster feeding. Overall our goals were to compare the frequency of cluster feeding between species and to document any changes over time and with successive molts. Tarantulas were housed in communal groups and we manipulated group size, prey mobility (live vs. pre-killed) and prey size to determine how these factors would influence social feeding occurrences. H. villosella had significantly higher occurrences of cluster feeding events but were also more likely to cannibalize tankmates. When cluster feeding occurred, H. villosella often had all group members in the cluster whereas H. gigas had only one cluster feeding event with all group members. Cluster feeding was not affected by prey mobility or prey size. Group size had no effect on latency to feeding. Prey mobility and size did significantly affect latency to feeding, with groups given live prey and smaller prey items feeding more quickly. Overall H. villosella responded to prey more quickly and H. gigas often did not feed, particularly in the large prey size groups. Growth rates were not affected by group size, prey mobility or prey size.
Evolution of the chelicera: a dachshund domain is retained in the deutocerebral appendage of Opiliones (Arachnida)
Prashant P. Sharma, Evelyn E. Schwager, Cassandra G. Extavour, Gonzalo Giribet
Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA
The proximo-distal axis of the arthropod leg is patterned by mutually antagonistic developmental expression domains of the genes extradenticle, homothorax, dachshund, and Distal-less. In the deutocerebral appendages (the antennae) of insects and crustaceans, the expression domain of dachshund is typically reduced. By contrast, the dachshund domain is entirely absent in the deutocerebral appendages of spiders, the chelicerae. It is unknown whether loss of dachshund expression in the spider chelicera is associated with the two-segmented morphology of this appendage, or whether all chelicerates lack the dachshund domain in their chelicerae. We investigated gene expression in the harvestman Phalangium opilio, which bears the plesiomorphic three-segmented chelicera observed in “primitive” chelicerate orders. Consistent with patterns reported in spiders, in the harvestmen chelicera homothorax, extradenticle, and Distal-less have broadly overlapping developmental domains, in contrast with mutually exclusive domains in the legs and pedipalps. However, unlike in spiders, the harvestman chelicera bears a distinct expression domain of dachshund in the proximal segment, the podomere that is putatively lost in derived arachnids. These data suggest that a tripartite proximo-distal domain structure is ancestral to all arthropod appendages, including deutocerebral appendages. As a corollary, these data also provide an intriguing putative genetic mechanism for the diversity of arachnid chelicerae: loss of developmental domains along the proximo-distal axis.
Patchy and mismatched cues: Pardosa milvina activity and survival influenced by two predators
**Michael Sitvarin, Kelsey Breen, Ann Rypstra
Miami University, Oxford, OH
Most prey species coexist with multiple predators that present different levels of predation risk. The wolf spider Pardosa milvina (Araneae: Lycosidae) detects and responds to chemotactile cues (i.e., silk, feces, excreta) deposited by predators traveling through the environment. We tested the responses of Pardosa to cues from the larger wolf spider Hogna helluo and the ground beetle Scarites quadriceps (Coleoptera: Carabidae), which distinctly different hunting modes. We examined changes in Pardosa activity and survival when different combinations of predator cues were present. We also used short and long food deprivation periods for Hogna and Scarites to investigate the role of hunger on the strength of response shown by Pardosa. Responses to cues from Hogna (decreased activity) were generally stronger than those from Scarites (increased activity). When simultaneously exposed to cues from both predators, Pardosa either responded only to Hogna cues or seemed to average its response to Hogna and Scarites cues alone. There was a significant effect of predator (i.e., Hogna and Scarites) food deprivation period on Pardosa behavior, with stronger effects seen at the higher hunger level. The type of predator cue present in the predation trials only had a significant effect on Pardosa survival when predators were at high hunger levels. Furthermore, Pardosa seemed to prioritize chemotactile information over visual and vibratory information when evaluating predation risk. Overall, it is clear that Pardosa is capable of integrating information from multiple predators and the potential risks they pose.
University of Alaska Museum of the North, University of Alaska, Fairbanks, AK
Females of the genera Dictyna and Emblyna represent an identification challenge , especially when collected without conspecifics. The two genera represent a morphologically similar, and likely closely related group which were considered to be of a single genera in the most useful identification publication, Chamberlin and Gertsch 1958. In an attempt to create an identification aid for females without conspecifics, internal female reproductive structures were examined. From an initial set of 34 species, representing all but one species group proposed by Chamberlin and Gertsch, it was found that the shape of the copulary tubes, location of the spermatheca, and location and shape of the external fovea all aided correct identification. These initial 34 species were also phylogenetically examined with a small morphologic data set, as well as general morphologic characters, and there is some evidence that the proposed species groups may represent artificial groups. This is an initial summary, as it is hoped that the project will be expanded to cover all Dictyna and Emblyna covered in Chamberlin and Gertsch.
The effects of perceived operational sex ratio and male density on mate-choice plasticity in a wolf spider, Schizocosa ocreata (Hentz)
**Brent Stoffer, George W. Uetz
Department of Biological Sciences, University of Cincinnati, Cincinnati, OH
Theory predicts that female mate preferences will vary depending on operational sex ratios (OSRs) in the population and/or the overall density of males. In the brush-legged wolf spider, Schizocosa ocreata, males typically mature in the field two weeks prior to females, which may allow females to assess potential mate availability before maturation to adulthood. Previous studies have shown that juvenile exposure affects adult female preference for male foreleg tufts, a secondary sexual characteristic. We used video playback in the lab to simulate changes in male density and sex ratio that females experience as penultimate instar juveniles. A full-factorial design, in which juvenile females were exposed to videos of one or three courting males at a frequency of once every two days or twice per day, was used for exposure. As adults, females were presented videos of courting males with small or large tufts. Female receptivity toward males with large tufts increased significantly with the cumulative number of males that females were exposed to as juveniles. Additionally, results suggest that a male-biased OSR plays a greater role in increasing female selectivity for males with large tufts than male density does. This study adds to the growing body of literature that suggests that invertebrates demonstrate plasticity in their mate choice decisions depending on their social environment.
Acoustic and seismic signal production in Gladicosa gulosa wolf spiders.
Alexander Sweger, George W. Uetz
Department of Biological Sciences, Cincinnati University, Cincinnati, OH
Many wolf spiders produce complex multimodal (visual/seismic) signals, while others rely entirely on seismic vibration, making them excellent models for testing hypotheses about the evolution of signaling behavior. The “purring” wolf spider Gladicosa gulosa has been widely overlooked in previous research, though early studies suggest that males of this species produce an airborne signal during courtship. The method of production of this airborne signal and its potential adaptive value is unknown. We examined acoustic/vibratory communication in G. gulosa. Using Laser Doppler Vibrometry and sensitive microphones, we recorded and characterized the components of male courtship. Results suggest that courtship displays by males of this species involve both airborne (acoustic) and seismic (vibration) signals, and that the components of these complex signals are produced by both stridulation and percussion mechanisms. However, the airborne component of the signal is fully ablated on a non-vibrating surface. Our data suggest that the airborne component of courtship in this species may be the indirect result of vibration of the substratum during courtship. We suggest that substrate resonance may play a role in production of the airborne signal, which could potentially have adaptive consequences in this species.
Singing in the rain: Seismic signaling of spiders on sodden substrates
George Uetz, Abbey Slaughter, Rhiddi Trivedi, Alex Sweger, Rachel Gilbert
Department of Biological Sciences, University of Cincinnati, Cincinnati, OH
Communication in complex environments poses challenges of potential signal loss, but some wolf spiders may compensate using multimodal signaling. Courtship of male Schizocosa ocreata (Hentz) is multimodal, consisting of visual and vibratory (seismic) signals. Previous studies have shown that efficacy of seismic communication varies with transmission properties of leaf litter microhabitat substrates. Because the 2011 field season had record-breaking levels of rainfall, we wondered whether adverse environmental conditions might dampen spider communication, and if leaf moisture affects seismic signals and mating success. We tested vibration transmission properties of wet vs. dry leaves using playback of both pure frequency tones and spider vibration signals. Dry leaves transmitted test tones and spider signals clearly, but wet leaves did not, obscuring signal structure across all frequencies. While wet leaves had higher levels of noise overall, dry leaves had higher signal to noise ratios. In addition, in dry leaves, signal amplitude may increase in a limited range of frequencies, suggesting potential for differences among leaves in resonance and/or signal filtering. Males courted females on wet and dry leaves equally, but mating success was significantly greater on dry leaf litter. Male spiders used significantly more visual signals (waves and arches) on wet leaves. Results suggest that although environmental conditions (e.g., heavy rains during the breeding season) can influence efficacy of individual signaling modes and negatively impact mating success, behavioral flexibility in multimodal signaling may compensate for constraints on communication.
The brown widow spider invasion of southern California: Assessment of egg parasites, microhabitat, and envenomation risk
Richard Vetter 1, Leonard S. Vincent 2, Doug W. R. Danielson 2, Amelia A. Itnyre 2, Kathryn I. Reinker 2, Daniel E. Clarke3
1 Department of Entomology, University of California Riverside, Riverside, CA
2 Division of Natural Sciences, Fullerton College, Fullerton, CA
3Department of Biological Sciences, Humboldt State University, Arcata, CA
Within the last decade, the non-native brown widow spider, Latrodectus geometricus, became well established in southern California such that it is now a very common urban pest species around homes. Because of its characteristic spiked egg sac and ubiquitous nature, homeowners are very familiar with this new invading species, are concerned about its toxicity and request control measures to contain populations. We investigated several aspects of brown widow’s natural history in this new environment. First, because egg sacs of native western black widows, L. hesperus, are occasionally infested with parasites, we examined brown widow egg sacs to determine if 1) these parasites would cross over to brown widow sacs, 2) if so, to what degree and 3) could this be expanded into a biocontrol program. We dissected 3,739 brown widow egg sacs with the most common biocontrol possibility being a 2% infestation by the egg predator chloropid fly, Pseudogaurax signatus. Second, we examined the microhabitat selection of brown widows. There is considerable environmental variation in southern California habitat including urban homes, landscaped parks, natural areas, and agricultural property. We collected brown widows and noted their location. Most brown widows were found within 1 meter of the ground, were very common around urban homes and urban landscapes such as parks (including predominantly in playground equipment) and were rare or absent from natural and agricultural areas. Of note, some of their habitat choice (under curled lips of potted plants, in recessed handles of garbage cans) increased their potential for human envenomation.
Assessment of foraging-site quality by a sheet-weaving spider
**Kelton D. Welch, Kenneth F. Haynes, James D. Harwood
Department of Entomology, University of Kentucky, Lexington, KY
The utilization of micro-sites by web-building spiders is a classical study in behavioral ecology, and provides important insights into the behavior of foraging predators. Traditionally, research has treated site utilization as consisting of two components — site selection (the initial decision to utilize a site) and site tenacity (the decision of how long to remain in the selected site). However, site utilization in the field is a complex behavioral process, and a dynamic, conceptual model of spider foraging behavior is needed to accurately understand this process. We ran two-way behavioral choice assays in a controlled, laboratory setting with constant monitoring throughout an entire nocturnal period to document and characterize the responses of foraging linyphiid spiders (Mermessus fradeorum (Berland)) to cues from their main prey item, Collembola. Spider responses to prey cues indicated a surprisingly sophisticated site-evaluation process, consisting of several dichotomous decisions made across a series of behavioral phases, encompassing the search for foraging sites and the construction of webs. Each phase of the process entails an increased investment of silk into the foraging site, suggesting that sheet-weaving spiders continuously evaluate the quality of foraging sites and regulate web construction accordingly to avoid wastage of silk. Additionally, the impact of prey cues differed across behavioral phases, indicating that other, non-prey-related cues (such as microhabitat structures and microclimates) are incorporated at specific stages in the decision-making process. These results provide new insights into the ecology of sheet-weaving spiders and the evolution of the sheet web.
The effects of recreational trails on cursorial spiders in California coastal sage scrub habitat.
Wendy Willis ¹, Dessie Underwood ²
¹ Aquatic Bioassay Consulting Labs, Ventura, CA
² Department of biological sciences, California State University at Long Beach, Long Beach, CA
We investigated the effects of recreational trails on cursorial spider communities in Point Mugu State Park located in Southern California. This is part of a larger study that included all cursorial arthropods and adult Diptera. Along three trails we placed three pairs pitfall trap arrays with one near the trail and the other 100m into the habitat. The pairs were placed at the trailhead, 500m along the trail, and 1000m along the trail. We sampled for two weeks in November 2004, April 2005, and June 2005. We collected 2109 spiders in 25 families in 51 genera. We analyzed our data at two ecological levels, a coarse level using community summary indices (species richness, species diversity, and number of individuals) and a fine level that compared the relative abundance of specific species using Bray-Curtis dissimilarity indices and permutational MANOVA. There was no impact of position on trail on spider species richness, spider abundance, Shannon’s H’, or Simpson’s diversity index. This is in contrast to the entire data set of all cursorial arthropods and adult Diptera where the abundance of individuals and species richness was greater closer to trails than trapping points 100 m from the trail and in the native habitat. At the fine level, we found that spider communities were significantly different across the three trapping dates and that trails were also significantly different from one another. Additionally, spider communities at the three distances from the trailheads were also different and that there was a trail by distance interaction.
Male-specific (Z)-9-tricosene stimulates female mating behaviour in the spider Pholcus beijingensis
Yong-Hong Xiao 1, Jian-Xu Zhang 2, Shu-Qiang Li 2
1 Jinggangshan University, Qingyuan District, Ji'an, Jiangxi, China
2 Institute of Zoology, Chinese Academy of Sciences, Beijing, China
Chemical signals play an important role in spider sexual communication, yet the chemistry of spider sex pheromones remains poorly understood. Chemical identification of male-produced pheromone mediating sexual behaviour in spiders has also not been reported before. This study aimed to examine whether chemically mediated strategies are used by males of the spider Pholcus beijingensis for increasing the probability of copulation. Based on data from gas chromatography–mass spectrometry (GC–MS) analysis, electroantennography (EAG) assay and a series of behavioural tests, we verified that (Z)-9-tricosene is a male-specific compound in the spider P. beijingensis. This compound acts as an aphrodisiac: it increases the likelihood that a female will mate. Mate-searching males release (Z)-9-tricosene to stimulate sexual behaviour of conspecific females. In the two-choice assay, however, sexually receptive females show no preference to the chambers containing (Z)-9-tricosene. This indicates that the male pheromone of P. beijingensis is not an attractant per se to the conspecific females. This is the first identification of a male-produced aphrodisiac pheromone in spiders.
Testing Color Change in Female Crab Spiders (Misumenoides formosipes and other Misuminae) and its Impact on Optimal Foraging
**Alissa G. Anderson and Dr. Gary N. Dodson
Department of Biology, Ball State University, Muncie, IN
Differential allocation of reproductive effort in male and female crab spiders is reflected in their extreme sexual size dimorphism as well as contrasts in their life histories. In Misumenoides formosipes the small, mobile adult males expend substantial energy finding and attempting to mate with females, whereas the large females are mostly sedentary and dedicated to foraging. We report on movement patterns, substrate choice, and life history traits that differ between the sexes. Another notable sex difference is the reversible color change capability found only in females. Changing between white and yellow allows a female to match the color of the inflorescence on which she is hunting and, hypothetically, appear cryptic to prey and/or predators. The rarity of this trait across animal species together with the apparent benefits suggests that significant costs are associated with color change. Neither costs nor benefits of color change in M. formosipes have been studied. Prey capture success of female M. formosipes will be tested in relation to color matching and mismatching through a series of trials in which females will be moved onto inflorescences of opposing and like colors. Digital photos will be used to quantify color values in the Lab color space component of Adobe Photoshop. We hypothesize that the tendency to tolerate the displacements will differ between white and yellow females due to different costs incurred, and that matched females will have greater prey capture success than unmatched females. Comparative observations with related species (Misumena vatia, Mecaphesa spp.) will be conducted whenever possible.
Spiders as potential biological control agents of stink bugs in cotton and soybeans
**Kacie J. Athey ¹, John R. Ruberson ², James D. Harwood ¹
1University of Kentucky, Lexington, KY
2University of Georgia, Athens, GA
Stink bugs (Hemiptera: Pentatomidae) have emerged as significant pests of cotton and soybeans in the southeastern United States with losses exceeding $70 million annually. Three of the most prominent pests are the southern green, Nezara viridula, green, Chinavia hilaris and brown stink bug, Euschistus servus. However, their predators are poorly understood, especially in respect to early season predation. As field observation of predation is difficult, molecular gut content analysis offers an alternative to traditional approaches. Consequently, species-specific 16S molecular markers were designed and used to discern the gut contents of active hunting spiders for stink bug consumption as well as some alternative prey sources, aphids and flies. Various spiders were collected throughout the summer in cotton and soybean in southeastern Georgia, and predation frequency was examined relative to prey availability. Predation rates were very low for all stink bug species. Our results showed that only Oxyopes salticus (Araneae: Oxyopidae) was feeding on stink bugs with various spider groups consuming both aphids and flies. These data suggest active hunting spiders are not playing a large role in the biological control of stink bugs, but further collecting in the early season is needed to fully understand the interactions between stink bugs and spiders.
Reflections on the tapetum lucidum and eyeshine in lycosoid spiders
Kari E. Benson1 and Robert B. Suter2
1Lynchburg College, Lynchburg, VA
2Vassar College, Poughkeepsie, NY
In the lycosoid spiders, the secondary eyes possess a grate-shaped tapetum lucidum that reflects light, causing eyeshine when these spiders are viewed with coaxial illumination. This guanine-based reflective surface is thought to increase visual capabilities in dim light. We explored the eyeshine of the posterior medial eye in eight taxa of pisaurid and lycosid spiders. We found that there were significant family- and species-level differences in both the reflected spectra and the intensity of reflection. While the peaks of the reflected spectra were in the green range for all spiders, the mean peak was further toward the blue end of the spectrum for the lycosids than for the pisaurids. Variation among species (about 54% of the total variation) was dominated by G. pulchra (Lycosidae) and D. vittatus (Pisauridae), both of whose spectra peaked near yellow, vs. V. avara (Lycosidae) whose spectra peaked to the blue side of green. The lycosid spiders showed overall brighter eyeshine. However, when corrected for their larger eyes, the lycosid spiders’ reflections were dimmer for their eye size than were those of the pisaurid spiders. These results demonstrate that the reflective qualities of the tapeta, and perhaps the absorptive qualities of other tissues and media that the light must traverse, vary widely among lycosoid spiders. This variation may signal both functional differences in visual capabilities and interesting developmental or selective histories within this clade.
Microhabitat and spatial complexity predict whip spider group size
**Kenneth J. Chapin
Department of Ecology and Evolutionary Biology, University of California, Los Angeles, CA
Although most amblypygid species are solitary and aggressive toward conspecifics, several Heterophrynus batesii can commonly be seen together on a single tree trunk. This study aimed to characterize the microhabitat preferences of H. batesii groups as a first step to understand these aggregations. I surveyed groups of amblypygids on the trail system of Tiputini Biodiversity Station bordering Yasuní National Park in Eastern Amazonian Ecuador in July and August 2010. Amblypygids were surveyed along with habitat and environmental data. Several measurements of trees associated with amblypygids were recorded, including those required to estimate surface area and calculate a Buttress Complexity Index. I compared these data to those of randomly selected trees to identify which microhabitat variables and spatial characteristics are selected by amblypygids. Heterophrynus batesii were found aggregated in groups of 2–8 animals. Groups used large, buttressing, complex trees with more leaf litter relative to those available.
Another event of independent evolution of color polymorphism in Theridiidae spiders in the Pacific Ocean?
**Darko Cotoras ¹, David Lindberg ¹, Rosemary Gillespie ²
1Department of integrated biology, University of California Berkeley, Berkeley, CA
2Environmental Science, Policy & Management Dept. University of California, Berkeley, CA
Convergent evolution is a recurrent phenomenon in the tree of life. It is usually explained by the adaptation of organisms to similar environmental conditions. Over the last few decades a series of examples of convergent evolution in color polymorphism have been described for the spider sub-family Theridiinae. The best studied of these is the Hawaiian happy face spider, Theridion grallator, which presents more than 20 variants. This color polymorphism was well known to parallel that of Enoplognatha ovata. More recently, a similar color polymorphism was described for T. californicum. There are also similar records for species present in Japan, Pohnpei and Fiji. In August 2011 after an expedition to Robinson Crusoe Island (Juan Fernández Archipelago, Chile), we found another species with a similar color polymorphism. Some morphs were identical to the Hawaiian species; meanwhile others were unique to Robinson Crusoe Island. The aim of this work is to locate the phylogenetic position of this species in order to verify whether its color polymorphism corresponds to an independent evolutionary event. To add the specimens from Robinson Crusoe Island and T. californicum to a previous phylogeny of the group, we amplified two mitochondrial (COI and 16S) and three nuclear genes (18S, 28S and H3). We conducted a Bayesian phylogenetic reconstruction for each gene separately and for all of them concatenated. We know that on the island there are six species from this family, two of them in the genus Theridion. But, the species identification is still in progress.
Cooperation and conflict during mating in an Opilionid
Kasey D. Fowler-Finn1, Owen G. Miller1, Emilia Triana2, Rafael L. Rodriguez1
1University of Wisconsin-Milwaukee
2University of Costa Rica
Mating interactions can exhibit qualities of mate choice or sexual conflict. For choice-based mating, females assess male displays during which males attempt to solicit cooperation from the female to achieve successful copulation. For conflict-based mating, females may resist male attempts to force mating, consequently screening for only those males capable of overcoming her resistance. Thus, both cooperation and conflict may allow females to select among potential mates for quality. We often consider choice and conflict as exclusive alternatives, but selection may favor the simultaneous occurrence of both. We tested whether selection has favored both choice and conflict in a common North American species of Opilionid, Leiobonum vittatum. To do so, we characterized several stages of mating and characterized the behavior as cooperative or conflict-based. We predicted that the more conflict-based behaviors would occur at earlier stages, and more cooperative/choice-based behaviors would occur at stages closer to copulation. Male-female interactions involved an initial struggle during which males attempt to lock their pedipalps onto the base of the female’s second pair of legs, and to wrap their third pair of legs onto distal portion of her second pair of legs. Males and females then exhibit assessment behaviors. Finally, the females appear to solicit the extension of the penis and to guide the penis towards her genitalia so that successful intromission occurs. This species show a shift from conflict to cooperation as mating progresses: initial contact involves more conflict-based behaviors, whereas closer to intromission, more cooperative behaviors occur.
Population Genetics of Phidippus audax from Michigan to Texas: Are there distinct Northern & Southern forms?
Department of Biology, Grand Valley State University, Allendale, MI
Phidippus audax is a common jumping spider found throughout North America from Canada to Mexico. Because it is so widely distributed, with a range encompassing distinct climates, and because regional color patterns have been reported, there may be genetically distinct northern and southern forms of P. audax. I collected samples from Michigan, Missouri, Oklahoma, and Texas, and sequenced approximately 1000 bp from the mitochondrial Cytochrome Oxidase I gene to determine whether these were consistent genetic differences between these populations. Preliminary results indicate that samples from Texas are genetically distinct from spiders collected at the other sites.
Influence of Acclimation on Prey Capture in Naïve Tarantula Spiderlings
**Joseph Edward Hill, Cara Shillington
Eastern Michigan University, Ypsilanti, MI
Several factors influence foraging success of newly emerged spiderlings, including experience, size, and environment. Spiderlings that forage successfully may experience increased growth rates, shorter intermolt periods, and larger size at sexual maturity. In this study, we compared prey capture success among three species of naïve tarantula spiderlings (Stromatopelma calceatum, Brachypelma angustum, and Pterinochilus murinus). We examined the role of prey size and acclimation on prey capture times and growth rates. Spiderlings were separated into acclimated and non-acclimated groups. Acclimated groups were introduced to feeding arenas five days prior to feeding while non-acclimated groups were introduced just prior to feeding. Each group was divided into two sub-groups based on prey size (20%-25% or 40%-45% of total mass). We measured prey capture times over several feeding trials and used spiderling mass as a measure of growth. Surprisingly, acclimation did not significantly impact prey capture times. While prey capture times were typically longest for the first feeding trial, they did not necessarily continue to decrease with successive trials. Prey capture times also varied among species; some species showed large decreases in prey capture times after just one feeding, while capture times for other species did not decrease until later trials. Prey size did not significantly influence percent mass gain, and weight-gain varied substantially among different species. Our results suggest that experience influences prey capture times, but is very species dependent, and energetic demands associated with growth rates also vary substantially with species.
Adaptively flexible courtship and mating behaviors in a cellar spider
Chad Hoefler1, Alyssa McDermott1, Ashley Ziegler1, and Ann Rypstra2
1Department of Biology, Arcadia University, Glenside, PA
2Department of Zoology, Miami University, Miami, OH
Classic sex role stereotypes include sexually passive and choosy females that invest heavily in offspring, and promiscuous and indiscriminant males who contribute only inexpensive sperm to their progeny. These stereotypes underpin many explanations for a wide variety of sex differences in morphology and behavior. However, organisms often live in variable environments; thus, sex roles should be a product of adaptively flexible individuals responding to an array of ecological variables. We were interested in partially characterizing the sex roles of the cellar spider, Pholcus phalangioides, to reveal the degree to which these behaviors are fixed or respond to environmental variability. Specifically, we examined the effects of adult sex ratio, food quality and quantity on mating interactions between males and females. We discovered that adult sex ratio and food quantity influenced both male and female mating behaviors, which showed high degrees of plasticity. We also discovered sex differences in the amount of time necessary for individuals to re-mate, and this difference was modulated by diet. The findings of our research link individual behavior to the characterization of sex roles and reveals levels of adaptive complexity that deserve more attention.
Kinship and familiarity affect recognition and foraging in Pardosa milvina
**Catherine Hoffman, Michael I. Sitvarin, Ann L. Rypstra
Department of Zoology, Miami University, Oxford, OH
An evolutionary explanation for altruism is critical to understanding social behavior and kin selection is the mechanism most commonly invoked for both phenomena. If animals live at high densities and are food limited they may interact with relatives competitively. Recent theory and empirical studies suggest that this situation may result in a higher tolerance for exploitation in producer-scrounger foraging relationships. We tested this hypothesis using the solitary wolf spider, Pardosa milvina (Araneae, Lycosidae) that exists in high densities in disturbed habitats of North America. Because P. milvina is chemically aware, we examined their activity on chemical cues and verified that they could discriminate between familiar animals and relatives. We then examined the foraging behavior of well-fed animals in the presence of chemical cues from hungry individuals. The cues presented included all combinations of siblings, non-kin, familiar and. unfamiliar spiders. Animals on cues from siblings took longer to capture prey and killed fewer prey. Familiarity with the animal producing the cues decreased the time to prey capture and increased the number of prey killed. Additionally, spiders consumed more of the prey they killed when on cues from a familiar conspecific. Thus, cannibalistic predator differentiated between relatives and familiar conspecifics and, while they actually left prey behind for hungry relatives, they were more voracious in the presence of familiar animals. Thus, well-fed foragers seemed to be more tolerant of exploitation by kin which may lead to foraging groups of relatives and help explain the early evolution of sociality in spiders.
Ladies’ choice: Female wolf spiders prefer multimodal over unimodal male courtship
Elizabeth C. Kozak, George W. Uetz
University of Cincinnati, Cincinnati, OH
Courting male wolf spiders use either multimodal (visual and seismic) signals or only seismic vibration, depending on the species. Previous studies of Schizocosa ocreata wolf spiders with live males as stimuli suggest individual signal modes are equally capable of eliciting female receptivity, but that multimodal cues enhance female response. In single presentation video playback studies, detection (latency to orient) and recognition (total receptivity displays) showed no significant differences with or without seismic cues. However, females may encounter more than one male at the same time. In paired choice video playback tests, orientation, approach and receptivity behaviors did not differ significantly when visual and seismic cues were presented alone. However, paired choice presentation of multimodal cues vs. unimodal visual or seismic cues showed significant differences in orientation, approach and receptivity behaviors. Females were more likely to be attracted to and respond with receptivity to multimodal cues than either mode alone. Results of multimodal video playback studies confirm earlier results with live males, and foster further manipulation of multimodal cues.
Exoskeletal Analysis of the Errant Scorpion Centruroides vittatus
Texas A & M International University, Laredo, TX
Behavior is limited by morphology. The errant scorpion Centruroides vittatus has shown behavior different than described in other scorpions. Centruroides vittatus climbs vegetation and rarely burrows while other scorpions studied rarely climb vegetation. The external morphology of the scorpion may be a factor that enables such behavior as climbing. Six scorpions were analyzed using a SEM at various magnifications ranging from 20000x to 100x to view the structure, texture, and shape of the scorpion exoskeleton. The difference in texture of the cuticle and also differences in shape and arrangement of seta were observed, as well as the folding of the arthrodial membrane in parts of the exoskeleton that move. The micrographs reveal that the setae in the legs of the scorpion are serrated while those on the palp and carapace are smooth and those on the chelicera are long and thin. The claws showed wear and also a distinct texture and had no seta. The micrographs also indicate that the tarsal spurs may move and this could be a factor in climbing.
Effects of Temperature and Glyphosate Exposure on Foraging in the Wolf Spider, Pardosa milvina (Araneae, Lycosidae)
**Megan Marchetti and Ann Rypstra
Miami University, Oxford, OH
Anthropogenic chemicals can have both unique and interactive effects on non-target organisms when experienced in combination with other stressors. While previous work has shown that a glyphosate-based herbicide alone affects activity and chemically-mediated behavior of the wolf spider, Pardosa milvina, limited research has been done regarding its effects when coupled with simultaneous abiotic stressors. Since glyphosate can be applied at multiple times during a growing season, it is possible that it may interact with changing temperatures and have graded effects on animals. Here we tested the hypothesis that glyphosate and temperature will have separate and interactive effects that impact foraging of P. milvina. For twenty-four hours, female P. milvina and pinhead crickets (Acheta domesticus) were housed in an arena with a treated substrate containing either glyphosate or water, at temperatures of 15, 25, and 35°C. The number of crickets alive, killed, and consumed was counted after each trial. Body measurements of each spider were also taken before and after trials as an additional measure of prey consumption. Results indicate that warming temperatures significantly increased both prey eaten and the change in abdomen width of Pardosa. In addition, the presence of glyphosate significantly increased superfluous prey killing. Thus, glyphosate and temperature independently affected foraging but we did not see evidence of additional interactive effects.
Biomimetic Analysis on the Spider Silk Apparatus for Designing the Electrospinning Nozzle
Myung-Jin Moon, Hoon Kim, Jong-Gu Park
Department of Biological Sciences, Dankook University, Korea
The biomimetic approach using various visualizing techniques on the cuticular spinning nozzles of the major ampullate silk glands in the golden-web spider Nephila calvata has been attempted to improve the design of nanofiber-spinning nozzle for electrospinning apparatus. The major ampullate spigot has the most effective nozzle system to produce nanofibers for dragline silk with high strength and elasticity. The excretory duct which transports the liquid silk feedstock from ampulla to spigot is divided into 3 limbs by loops back on itself to form an S-shape morphology. Final diameter of the nanofibers at nozzle was dramatically reduced by gradual narrowing of duct cuticle less than 10 times comparing to its original size of funnel region. Moreover, the funnel has a characteristic cuticular organization with porous microstructure which seems to be related to water removal from feedstock of silk precursors. High magnification electron micrographs also reveal the presence of the spiral grooves on the surface of the cuticular intima near the valve which presumed to reduce friction during rapid flow of liquid silk.
Fine Structure of the Spinning Nozzle of the Dragline Silk in the Spider Nephila clavata
Myung-Jin Moon, Hyo-Jeong Kim, Yong-Ki Park
Department of Biological Sciences, Dankook University, Korea
The dragline silk with high elasticity and strength is produced finally from the nozzle of the spigot on the anterior spinneret as the feedstock passes through the funnel of the duct. The duct of the major ampullate gland in Nephila clavata has the function to polymerize the dragline silk with the mechanisms of water absorption, ion exchange and physical pressure. By the fine structural image analysis using high quality field emission electron microscope, the presence of cuticular cavities which distributed along the third limb of the duct was first noticed. Histologic examination reveals that the epithelial flask-shaped cells are distributed to the exocuticle layer through these cavities. In addition, we could find helical grooves which reduce frictions and facilitate the spiral movement of the feedstocks during the passage of cuticular surface of the duct. It assumed that these cuticular cavities and helical grooves also contribute to the major production procedure from liquid feedstocks to insoluble dragline silk.
Estimating physical performance: A study of body condition in the Wolf Spider, Schizocosa ocreata
Kimberly Morsch, Kevin Morahan, Jennifer Bosco, Brian Moskalik
College of the Holy Cross, Worcester, MA
In natural conditions, spiders are usually food limited and must compensate for this in order to survive and reproduce. Because these organisms have a hydrostatic skeleton, intake of both water and food may drastically alter their ability to function and survive. When spiders are met with such environmental stressors, they must adjust their physical responses to stimuli or avoid further expenditure to conserve energy. In this study, we tested the effect of water and food limitations on the performance of the wolf spider Schizocosa ocreata. Two separate feeding regimens (food limited and food abundant) were maintained for approximately 5 weeks. After which, body measurements were taken and spiders were run until exhaustion. A second trial round was implement after removing water from half of each feeding treatment for an additional 5 days. All spiders were then measured again as in the previous. Results indicated that both food and water availability impact spider survival, body condition and physical response to stimuli (performance). However, those given limited food and water were similar in performance attributes: peak speed and expenditure duration. This study consequently reveals that spiders can alter physiological processes under suboptimal conditions and may additionally provide insight into how these organisms adjust to such stressors in particular environments. Additionally, the use of Body Condition Indices as predictors of performance will be discussed.
Communication and Courtship Behavior in the Ischnocolid tarantula Heterothele villosella
Brian Moskalik, Jennifer M. Bosco
College of the Holy Cross, Worcester, MA
One of the earliest divergences on the evolutionary tree of (Arachnid) spiders represents the mygalomorphs, this group includes the tarantulas and funnel web spiders. Consequently, mygalomorph communication and courtship has been generally characterized as quite simple, where a male invests minimally in courtship when in the presence of a female and mates with her while she remains relatively inactive or unselective. This courtship sequence leaves little variation for sexual selection to act on, virtually eliminating mate choice pressure. We aim to examine the actuality of these claims by analyzing mating interactions in the Ishnocolid tarantula Heterothele villosella. This species lives in relatively high population densities and displays a quasi-social or communal lifestyle. From these observations, we have been able to establish that, contrary to anecdotal accounts, male tarantulas display a complex range of behaviors that are influenced by female behavior. These interactions are highly dynamic since females prove not to be passive players but control whether or not a male continues courtship, successfully copulates or is rejected. Without female cooperation, males will not be able to attain a copulatory position or may be rejected and cannibalized. We argue that this female interaction is evidence of sexual selection pressure acting on males and has the ability to shape how courtship proceeds (courtship duration, male vigor, etc). This study shows that while phylogenetically “primitive”, not all tarantulas are behaviorally simple.
Male courtship behavior by temperature for the wolf spider Schizocosa ocreata
Bernard Paniccia 1, J. Andrew Roberts 2,
1 Department of Evolution, Ecology, and Organismal Biology, The Ohio State University, Columbus OH
2 The Ohio State University at Newark, Newark, OH
The courtship behavior of wandering spiders, such as jumping spiders (Salticidae) and wolf spiders (Lycosidae), commonly includes active visual and seismic signals. The vigor (rate and duration of bouts) with which these signals are produced may directly influence mating success in many species. As spiders are ectotherms, the temperature of the environment can have a significant effect on metabolism and behavioral performance (vigor). In order to better understand temperature effects on vigor, courtship behaviors were observed for male wolf spiders (Schizocosa ocreata) exposed to conspecific female silk and chemical cues. Rate and duration of specific courtship behaviors were analyzed within a range of 0 to 40 ˚C. Analysis indicates that spiders behaved as expected based on previous data collected for another wolf spider, Schizocosa bilineata (Roberts et al., in prep), that is, rate of behavioral bouts increased with increasing temperature and total duration of courtship behaviors increased. If increased courtship vigor increases the probability of reproduction, these results suggest that males of this species should behave in a manner that maximizes their body temperature relative to competitors. Future work on these species will evaluate the significance of these body temperature controlled behaviors.
Foraging strategy of Argiope trifasciata from a biomechanical perspective
**Dakota Piorkowksi, Samuel Evans, Todd Blackledge
Department of Biology, University of Akron, Akron, OH
Secondary consumers face selective pressure from trade-offs involved with adaptive foraging. The daily web-constructing behaviors of orb-weaving spiders (Araneoidea) make them interesting models to study when considering these trade-offs. In response to hunger levels and prey availability the diurnal orb-weaver, Argiope trifasciata has the ability to alter web area. We predicted a change in behavior as the success rate of prey encounter diminishes. Because silk composition is partially dependent on diet, we also predicted a measurable change in silk performance. To test our predictions, we starved individuals collected from Bath Nature Preserve for 8-day periods in laboratory settings. Two treatments were set up, one that was fed a day prior to the start of the 8-day period and another that was left unfed. This was to control for variation from differences in foraging success prior to the experiment. Response to prey capture failure was quantified by taking measurements of mechanical performance of capture and ampullate silk, several web parameters and aggregate glue investment. Using repeated measures ANOVAs, we found that capture silk stickiness decreased over time when mechanically tested. This was accompanied by increases in silk strength, total capture area and capture silk volume. Unfortunately, due to small sample sizes, we were only able to find marginally significant p-values. Results of this experiment, however, imply that there are several trade-offs made to counter the material performance of aggregate glue within capture silk, which is likely due to a dietary constraint.
Terra incognita: New species and major range expansions of Opiliones in the United States
Jeffrey W. Shultz
University of Maryland, College Park, MD
The invertebrate fauna of the eastern United States is one of the most intensively studied in the world and thus the discovery of a radiation of large-bodied terrestrial arthropods would be surprising. Yet, recent work on the taxonomy of harvestmen has revealed nearly 20 new species, including a heretofore unknown radiation in the genus Hadrobunus. In the last three years, Hadrobunus in the eastern U.S. has expanded from two poorly delimited species to at least 15 distinct species, with only one resulting from a transfer of a previously known Leiobunum species. New undescribed species of Leiobunum are known from Arizona and Nebraska, and two more – L. euserratipalpe Ingianni et al. and L. hoffmani Ingianni et al. – have recently been described. A new species of the peculiar triaenonychid Fumontana (Laniatores) has been discovered in the vicinity of Gainesville, Florida. Major range expansions have also been found, including the discovery of a specimen of the rare Acropsopilio boopis from the mountains of western North Carolina. This is a southern range extension of over 450 miles and is the first specimen recovered outside the post-glacial north. These findings are derived from limited, untargeted and spotty sampling and suggest that much remains to be learned about the harvestman fauna of the United States, especially in the under-studied South.
Lack of trait-mediated effects of predators on detritivore activity
Michael Sitvarin, Ann Rypstra
Miami University, Oxford, OH
Generalist arthropod predators have been shown to impact the grazing component of terrestrial food webs, and a growing collection of studies make progress towards characterizing the role of spiders and beetles in detrital food webs. Historically, researchers have manipulated the predator community (e.g., removed spiders) and measured changes in detritivore abundance or ecosystem function (e.g., nutrient cycling), but detailed behavioral observations are lacking. Here, we examined the response of Sinella curviseta (Entomobryomorpha: Entomobryidae) to chemotactile cues (silk, feces, excreta) from four potential predators: wolf spiders (Araneae: Lycosidae) Pardosa milvina, Hogna helluo, Rabidosa rabida, and a beetle (Coleoptera: Carabidae), Scarites quadriceps. We anticipated reduced activity in response to cues from Pardosa, though none of the larger predators were expected to elicit a response. The activity of individual Sinella was quantified using motion capture software in a split arena containing cues from a single predator paired with unmanipulated substrate. Sinella activity did not differ between the untreated arena side and the portion containing predator cues. The lack of response to cues from Hogna, Rabidosa, and Scarites may be adaptive, as these predators are unlikely to consume Sinella. Cues from Pardosa did not cause an activity change, which may indicate that Sinella does not avoid areas where predators are present. Instead, Sinella may rely on predator avoidance tactics (i.e., jumping) upon contact with a predator. Although it appears that trait-mediated interactions between Sinella and Pardosa are unimportant, the effects of cues from Pardosa may manifest in aspects of Sinella behavior other than movement.
Trachyzelotes lyonneti (Auduoin) (Araneae: Gnaphosidae) in south Texas
**Amelia Solis, Dan Mott
Texas A&M International University, Laredo, TX
Twenty-two specimens of the introduced spider Trachyzelotes lyonneti (Auduoin) were collected from March to June over a 4 year period (2008-2012). All of the specimens (7♂ & 15 ♀) were collected in Webb County, Texas and all but 3 of the specimens were collected in pit-fall traps in propylene glycol. Generic and specific characters of males and females were prepared and examined with a scanning electron microscope at magnifications ranging from 35- 5,000 X. The dorsal view of the cleared epigynum was photographed under a dissecting microscope.
Evolution of spider silk genes in cob-web weaving spiders
Daniel Todd ¹, Elizabeth Brassfield ¹, Cheryl Hayashi ², Peter O'Donnell ¹, Patrick Oley¹, Nadia Ayoub ¹
Washington and Lee University, Cary, NC ¹
University of California, Riverside, CA ²
Orb-web weaving spiders and their relatives (Orbiculariae) make task-specific silks that originate from specialized abdominal glands. Silk fibers are composed of one or more unique structural proteins called spidroins (spider fibrous proteins), which are members of a gene family. Different spidroins are expressed in different gland types. For example, MaSp1 and MaSp2 form dragline silk and originate in the major ampullate glands. We are describing each member of the spidroin gene family from three closely related species of cob-web weavers, the western black widow, Latrodectus hesperus, brown widow, L. geometricus, and the false black widow, Steatoda grossa (Theridiidae). Our goals are to determine relationships among spidroin members and evaluate rates and patterns of evolution in this gene family. These species are an ideal model for evolution of silks because they possess dragline silks that vary from the weakest known (false black widow) to the strongest known (black widow) despite their close relationship. We constructed libraries of genes expressed in silk glands of the brown and false black widows and identified genes encoding most types of spidroins, include ones incorporated into dragline silk (MaSp1 and MaSp2), minor ampullate silk (MiSp), prey-wrapping silk (AcSp), egg case silk (TuSp), and attachment cement (PySp). AcSp and TuSp group together in spidroin gene trees suggesting that one is an ancient copy of the other. These spidroins are also the most conserved among cob-web weaving species. We will discuss potential sources of selection on spidroins that form functionally distinct fibers.
Immature Hogna helluo (Araneae, Lycosidae) display anti-predator behavior in response to chemical cues from conspecific adults
Aaron Tolin ¹, Matthew H. Persons ², Ann L. Rypstra ¹
1Miami University, Oxford, OH
2Susquehanna University, Selinsgrove, PA
A spider’s capability to utilize available information from its habitat in reducing predation risk is advantageous to its survival at all points in its career. Two experiments were designed to investigate whether immature Hogna helluo (Araneae: Lycosidae) shows a behavioral response to chemical cues (silk draglines, feces and other excreta) left behind by adult Hogna in the environment. The first experiment examined the activity of immature Hogna when encountering chemical cues from an adult. Juvenile Hogna were released in a small neutral space between one side with adult cues and the other side with nothing and then monitored for 15 min. we found statistically significant decreases is the juvenile’s total travel distance, time spent moving, and time spent ambulatory while on chemical cues from their adult counterparts. In the second experiment juvenile Hogna were given the choice of moving to different regions of a rectangular arena containing adult cues or nothing. The spider was released in the neutral zone and its location in the box was noted at the end of twenty-four hours. Juvenile preferred to reside in the cue free territory when given the choice. Thus, immature Hogna exhibited the ability to recognize and utilize information in chemical cues left by conspecific adults. There is a premise for further research into the ontogeny shift in the ecology of juvenile Hogna, and especially its intriguing mid-career relationship to its intraguild competitor, Pardosa milvina.
The effects of the glyphosate-based herbicide on the foraging patterns of predatory wolf spiders
Alex Webb ¹, Sandra Rittman 2, Samuel Evans 3, Ann Rypstra 4
1California State University, Sacramento, CA
2Ohio State University, Columbus, OH
3Rice University, Houston, TX
4Miami University, Oxford, OH
Many studies have shown that non-target taxa in glyphosate-sprayed environments are not directly affected by this herbicide. Indirect effects, however, have been shown to exist. For example, in the wolf spider Pardosa milvina (Araneae, Lycosidae) glyphosate alters both mate-finding and locomotor behavior. In this study, we examined the effects of glyphosate on the foraging behavior of two wolf spider species common to agricultural fields in Ohio, Hogna helluo (Araneae: Lycosidae) and Pardosa milvina. Experiments were conducted by allowing the spider predator to lay down chemotactile cues in an arena prior to trials. Either a commercial formulation of a glyphosate-based herbicide or distilled water was then applied to patches of the arena before a prey species, either P. milvina or Acheta domesticus (Orthoptera: Gryllidae), was presented. Trials were then repeated with P. milvina as predator and A. domesticus as prey. All predator-prey interactions were recorded and scored. Hogna helluo oriented toward and captured both prey species more quickly when glyphosate was present. Herbicide had no effect on the orientation or capture time for P. milvina, but it increased the number of attacks required to capture A. domesticus. Our results show that glyphosate is having indirect effects on the foraging behavior of these wolf spiders, and that the effects are species dependent.
Tracking predation shifts in forest spiders over the cold season
**Thomas D. Whitney, James D. Harwood
Department of Entomology, University of Kentucky, Lexington, KY
Forest-dwelling spiders are thought to feed opportunistically during times of low prey availability. This is complicated, however, by the fact that prey populations show considerable spatio-temporal variation, and many of these prey items are of poor nutritional quality. The primary objective of this research was to identify seasonal spider predation patterns in response to fluctuations in prey availability, focusing on shifts in foraging dynamics during the autumn, winter, and early spring where there is the greatest paucity of information. Within an eastern deciduous forest ecosystem, prey availability was monitored and, in parallel, spiders were collected for molecular gut-content analysis in order to delineate predation strength throughout the season. Prey availability and predation were correlated to ultimately identify reliance and food preference patterns of these predators. Tomoceridae (Collembola), an important prey item for eastern forest spiders, remained active but decreased throughout the winter. In contrast, dipterans fluctuated in activity and increased significantly during February thus providing a critical pulse resource for these predators as alternative food items decreased in abundance. The dominant spiders of the forest, from the genus Schizocosa, were collected throughout the cold season for molecular gut-content analysis. These predation results and their correlation with available prey will be discussed. Tracking seasonal feeding dynamics between spiders and their prey provides valuable insights into their functional role in forest floor food webs.
Female receptivity towards sequentially courting males of varying quality in Schizocosa ocreata
Maggie Williams, Brent Stoffer, George W. Uetz
Department of Biological Sciences, University of Cincinnati, Cincinnati, OH
In the wolf spider, Schizocosa ocreata (Hentz), males possess dark pigmentation and tufts on their forelegs that are a conspicuous secondary sexual characteristic. Previous studies have shown that, when given a choice, females demonstrated increased receptivity towards males with large tufts over males with small tufts. In trials with two males, females frequently mated with the males that courted first. However, it has yet to be investigated whether female receptivity changes when males of varying quality are encountered sequentially. This is a particularly interesting question in the context of eavesdropping behaviors, as male “interlopers” could use courtship signals to locate and intercept potential mates. We used video playback to introduce females to a courting male, followed by a second courting male interloper thirty seconds later. The second (interloper) male had tufts of greater, lesser, or equal size relative to the first male. When the first male had average-sized tufts, there was no effect on female receptivity towards the second male. However, when the first male had reduced tufts and the second male had enlarged tufts, females’ latency to approach the interloper male video was significantly shorter. Additionally, the females were more likely to be receptive and showed more receptivity displays towards the second male. These results suggest that eavesdropping behavior could be beneficial for a male, depending on the relative quality of the first and the second male encountered.
The effects of autotomy and nutrition on the weight-specific resting metabolic rates and development of orange baboon tarantula (Pterinochilus murinus) spiderlings
**Brenan Wilson, Cara Shillington
Eastern Michigan University, Ypsilanti, MI
Autotomy, or voluntary limb-loss, is a technique employed by spiders to escape predation or discard damaged legs. With successive molts, the limb is regrown and the fitness costs of autotomy often seem to be minimal. We performed a preliminary investigation of the effects of autotomy on the weight-specific resting metabolic rates (WSRMRs) of orange baboon tarantula (Pterinochilus murinus) spiderlings. We hypothesized that regenerative growth, which eventually produces limbs indistinguishable in size from those produced by developmental growth, results in greater metabolic demands. We also investigated the interactive effects of nutrition and autotomy on regenerative growth and metabolic rates, and hypothesized that nutritional limitations reduce WSRMRs and the effects of autotomy. Second instar spiderlings were divided into four autotomy-nutrition treatments. Autotomy was induced by holding the second and third legs of one side with forceps until they were dropped. Spiderlings were fed with feeder crickets bi-weekly following either a low nutrition (2.5-7.5% body weight) or high nutrition (20-25% body weight) diet. Metabolic rates were measured bi-weekly using flow-through respirometry. Leg removal had a stronger influence on WSRMR than nutrition initially, but nutrition seemed to play the greater role after about six weeks. Differences in WSRMRs lacked statistical significance; however, though inconclusive, the data suggest that further research is needed. Most interestingly, 100% mortality without molting occurred in the un-autotomatized low nutrition treatment, while in the autotomatized low nutrition treatment only 40% died without molting and 40% successfully molted. These differences may be explained by cellular repair pathways.
Blind Dating: The role of different eye rows in female mate recognition by the wolf spider Schizocosa ocreata (Hentz)
Rebecca Wilson, Tess Piening, George W. Uetz
Department of Biological Sciences, University of Cincinnati, Cincinnati, OH
Female Schizocosa ocreata wolf spiders utilize visual cues from males (tufts on forelegs and visual signals) in mating decisions. As wolf spiders have eight eyes in two sets of different sizes and orientations, we tested the hypothesis that the anterior (small) and posterior (large) eyes play different roles in detection and decision-making processes involved in mate choice. We occluded different eyes of individual females using an opaque, non-toxic paint, and presented them with video playback of a courting male. When the posterior eyes were occluded, there was a significantly longer latency (seconds) to orient, as well as to respond to males with receptivity when compared to unmanipulated controls. This suggests the posterior eyes are involved in mate detection and recognition. There was no statistically significant difference in mean latency to orient between unmanipulated controls and females with anterior eyes occluded, and no differences in female receptivity displays were seen among all treatments. The data suggest that the two sets of eyes may have different roles in detection and identification of courting males (with posterior eyes playing a more important role), although both eye sets may be equivalent in mate assessment by females once mate recognition has occurred.