Thirty-First
Annual
Meeting Susquehanna University Hosted by Matt Persons |
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Friday, July 13th Archived July 18, 2007 |
Use the table below to jump to abstracts, alphabetized by first author
Molecular insights into social structure and evolution of sociality in Anelosimus (Theridiidae) |
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Author |
Institution |
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Ingi Agnarsson |
Department of Biology, University of Akron |
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Abstract: While spider sociality is scattered across ~13 tiny clades (1-2 spp each) in the order, roughly half of all social species are concentrated in a single clade; the cobweb spider genus Anelosimus. Morphological phylogenetic work to date has suggested that even within Anelosimus sociality similarly has evolved repeatedly. This suggests that at both taxonomic levels the same pattern holds: multiple origins of sociality but low diversification of lineages once social. Interestingly, each time sociality arises, it is accompanied by a switch to inbreeding and results in strikingly similar social structure. Here, we address several questions surrounding sociality and its evolution using molecular data. We find that the molecular data agrees well with the morphological phylogeny, confirming multiple independent origins of sociality. Within the social A. eximius we see a pattern of colony propagation by single matrilineages and absence of colony mixing, suggesting faithful inbreeding within colonies. Across species we find evidence of the consequences of sociality on population genetic patterns. Social species show lowered sequence divergence both in mitochondrial and nuclear data as compared to the outbred subsocial species. This suggests that inbreeding and other consequences of sociality, such as high turnover and small effective populations sizes, lead to loss of genetic variability. If genetic variation is the basis of evolutionary potential of species to respond to environmental change and disease, then lowered genetic diversity in the inbred social spiders may help explain their low diversification and relatively brief persistence in evolutionary time (posted June 18, 2007)
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Microhabitat selection and movements of harvestmen (Opiliones: Phalangida) in gardens |
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Authors |
Institution |
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| Timothy J. Bankroff | Department of Zoology |
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| Alan B. Cady | ||
Abstract: Harvestmen are ubiquitous and abundant generalist predatory arthropods, yet little is known about their ecology and behavior. They are known to consume a variety of pests, and due to their prominence in agroecosystems, great dispersal ability, and gregarious tendencies, they may have potential as agents of biological control in gardens. This study used mark and recapture methods to investigate the feasibility of sustaining a harvestman population (Opiliones: Phalangida) in a garden. Unrestricted harvestmen movements were systematically followed and small, wooden shelters shaped like lean-tos were placed as diurnal refugia for these humidity-sensitive predators in an attempt to prevent their emigration. Furthermore, it was predicted that more harvestmen would be observed in dense vegetation where microclimatic conditions (temperature & humidity) should be more favorable during the day. Significantly lower daytime temperatures and reduced temperature variability were recorded in denser vegetation. More harvestmen inhabited dense vegetation than areas of sparse or no vegetation. Significantly more harvestmen were observed in the proximity of shelters, thus, adding shelters reduced their tendency to leave the garden. The range and movements of harvestmen tended to be less in areas of dense vegetation and near shelters than in more exposed areas. (posted June 15, 2007) |
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Family ties: molecular phylogeny of crab spiders (Araneae: Thomisidae) |
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Author |
Institution |
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| Suresh P. Benajmin | Department of Entomology, National Museum of Natural History |
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Abstract: The first quantitative phylogenetic analysis of three sequenced genes (16S, CO1, H3) of 25 genera of crab spiders and 11 outgroups supports the monophyly of Thomisidae. Four lineages within Thomisidae are recovered. They are informally named here as the Borboropactus clade, Epidius clade, Stephanopis clade and the Thomisinae clade, pending detailed morphology based cladistic work. The Thomisinae clade is recovered as a strongly supported monophyletic group with a minimal genetic divergence. Philodromidae previously widely considered a subfamily of Thomisidae do not group within thomisids. However, Aphantochilinae previously generally considered as a separate family groups within thomisids. (posted June 19, 2007)
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Resources for research on arachnids and other non-insect arthropods at Carnegie Museum of Natural History, Pittsburgh |
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Authors |
Institution |
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| Charles W. Bier | Section of Invertebrate Zoology, Carnegie Museum of Natural History |
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| John E. Rawlins | ||
| James W. Fetzner, Jr. | ||
Abstract: The Section of Invertebrate Zoology at Carnegie Museum of Natural History (CMNH) is recognized worldwide for insect collections exceeding 11 million specimens. Non-insect resources at CMNH are less well known and infrequently used, especially non-acarine Arachnida and crayfish (Crustacea: Astacoidea). On-staff expertise was limited until recently; now a visiting curator works on crayfish (JWF) and a research associate on spiders (CWB). Historic arachnid holdings include Brazilian spiders of H.H. Smith (1880’s), and Pennsylvanian spiders from B. Vogel (1960’s). Since 1985 extensive trap-based collecting worldwide has provided sample residues containing diverse arachnids. The A. Ortmann Crayfish Collection (1900’s), with recent material from Nearctic and Australian regions, comprise crustacean holdings exceeding 2,000 lots. Collection facilities have been renovated since 1981 by four NSF grants. Storage in standardized glassware is far-advanced, and emphasis placed on curating new material from fieldwork and historical samples. Collections are associated with library materials including most pre-1950 literature; post-1950 coverage is less comprehensive, but actively supplemented as collections require. Information initiatives for arthropod specimens are expanding (links from homepage http://iz.carnegiemnh.org/inverts/izhome.html). On-line databases will cover crustacean and arachnid holdings as curation permits. Web-based projects include compiling a list of Pennsylvania spiders using the "Catalog of Pennsylvania Biodiversity", a web-accessible checklist of specimens documenting Pennsylvania occurrence. CMNH hosts “Global Crayfish Resources” developed by JWF, including a taxonomy browser, checklists, discussion forum, and International Association of Astacology’s homepage. CMNH endeavors to make non-insect arthropod resources accessible to active investigators interested in systematics, faunistics, and issues related to conservation and resource management. (posted June 19, 2007)
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Evolution of the sphingomyelinase D gene family in sicariid spiders |
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Authors |
Institutions |
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| Greta J. Binford | Lewis & Clark College |
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| Pamela Zobel-Thropp | ||
| Melody Rynerson | ||
| Scott Burns | Cleveland High School Portland, Oregon USA |
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Abstract: Spiders in the family Sicariidae are well known for bites that cause dermonecrotic lesions in mammalian tissues. The venom toxin sphingomyelinase D (SMaseD) is a sufficient causative agent for lesion formation. This toxin is a member of a gene family about which little is known with respect to patterns of variation of venom-expressed paralogs within and among species. Understanding these patterns allows inference of mechanisms of evolution underlying the diversification of this toxin, and has relevance for understanding risks and treatments of bites. To date, inferring evolutionary mechanisms influencing these toxins has been limited by sparse taxon sampling of venom-expressed SMase D genes. We have isolated and sequenced SMase D cDNAs from representatives of all currently described species groups of Loxosceles and Sicarius and representatives from all continents on which they are native. Phylogenetic analyses of relationships among SMase D genes in comparison to patterns of relationships of species as inferred from 28s, CO1 and ND1 indicate that (a) the number of SMase D paralogs expressed in venoms may vary across species ranging from 3 to at least 7; (b) duplications are frequent in the SMase D family lineage. (posted June 19, 2007)
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Functionally independent components of prey capture are architecturally constrained in spider orb webs |
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Authors |
Institutions |
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| Todd Blackledge | Department of Biology, University of Akron |
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| Chad M. Eliason | Department of Curricular and International Studies, University of Akron Akron, Ohio USA |
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Abstract: Orb webs first intercept and then retain insects long enough to be attacked by spiders. Improving either function increases prey capture and they are largely determined by different aspects of web architecture. We manipulated the mesh width of orbs to investigate its effect, along with web size, on prey capture by spiders and found that they functioned independently. Probability of prey capture increased with web size but was not affected by mesh width. Conversely, spiders on narrow meshed webs were almost three times more likely to capture energetically profitable large insects, which demand greater prey retention. Yet, the two functions are still constrained during web spinning because increasing mesh width maximizes web size and hence interception while retention is improved by decreasing mesh width because more silk adheres to insects. The architectural coupling between prey interception and retention has likely played a key role in both the macroevolution of orb web shape and the expression of plasticity in the spinning behaviors of spiders. (posted June 18, 2007)
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Variation in the material properties of the silk in the common house spider |
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Authors |
Institution |
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| Cecilia Boutry | Department of Biology, University of Akron |
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| Todd Blackledge | ||
Abstract: Spider webs are capture devices that depend upon both web structure and mechanical performance of the silk fibers to capture prey. Alterations in the material properties of these silk fibers could therefore change web function, but there is little direct evidence for this. We investigated the mechanical performance of the silk of Achaearanea tepidariorum (Araneae: Theridiidae) fed two different types of prey (large, fast crickets versus small, slow isopods) for one week. A. tepidariorum spins a cobweb composed of several main structures, including supporting threads, and gumfooted line capture threads. By comparing silk within each component, we found that silk in the support region of cobwebs was tougher, and more elastic when spiders were fed crickets. In contrast, the material properties of the gumfooted capture threads of cobwebs did not differ between the two groups of spiders. Thus, spiders fed larger prey seem to spin stronger supporting threads that break at higher extension. They also spun thicker, and therefore stronger, fibers. However, spiders fed large prey tended to be in better body condition than spiders fed smaller prey, despite receiving overall equal amounts of food. Therefore, it is unclear whether this variation in mechanical properties is a response to the type of prey itself or to differences in relative body conditions of spiders. Whatever causes this variation, spiders fed large prey spun more robust webs, able to resist to high kinetic-energy prey and support heavier spiders. (posted June 15, 2007)
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Biogeography of spiders across the boreal-tundra transition |
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Authors |
Institution |
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| Joseph J Bowden | Department of Entomology, McGill-Macdonald College |
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| Christopher M Buddle | ||
Abstract: Spiders (Arachnida: Araneae) are ecologically important arthropods that exhibit high global diversity and are well-represented in northern ecosystems. Areas such as north-western North America, which possess some of the highest rates of endemism, remain largely understudied compared to temperate zones. Spiders were collected in pit-fall traps from early June to mid August 2005 along 500 km of the Dempster Highway in the Yukon to examine effects of this latitudinal gradient and habitat transition on terrestrial arthropod richness, composition and abundance. Over 100 species have been identified and species show varying responses to the gradient. The two habitats seem to be important in determining species composition, however, no significant differences were found in species richness or abundance along the sampled transect. (posted June 7, 2007)
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Leg autotomy affects both terrestrial and aquatic locomotion in the wolf spider Pardosa valens (Part 2) |
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Authors |
Institutions |
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| Christopher A. Brown | Department of Biology, Tennessee Tech University |
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| Daniel R. Formanowicz, Jr. | Department of Biology, University of Texas at Arlington Arlington, Texas USA |
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| C. Christopher Amaya | Biology Department, Siena College |
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Abstract: Many spiders voluntarily amputate (autotomize) a leg as an antipredator behavior. While beneficial in the short term (as it can allow the spider to survive encountering a predator), leg autotomy may have detrimental effects over the longer term. In several species of wolf spiders, leg autotomy causes a reduction in burst sprint speed, an important trait both for avoiding predators and capturing food. In our first experiment we examined burst sprint speed before and after leg autotomy in males and females of the riparian-zone wolf spider Pardosa valens during June 2005. Since this species moves readily both on land and the water surface, we conducted experiments in linear race tracks mimicking both these surfaces. In terrestrial trials, males and females did not differ in speed, but both sexes ran significantly slower following loss of a leg. In aquatic trials, females ran significantly faster than males, and leg loss led to a significant decrease in speed for males but not females. We also found a potential temperature effect, as spiders run in the evening (when they were presumably warmer) were generally faster than those run during the morning. Despite females weighing nearly twice as much as males, all of the above results held when adjusting for body mass. Finally, males were less likely to run on the aquatic track, and to go shorter distances when they did run, than were females. We repeated the above trials for females only during July 2006, and found no significant effects of autotomy or temperature on female running performance. These results suggest that both aquatic and terrestrial locomotion can be impaired by leg loss in P. valens, but that these costs may differ between sexes and age or season. (posted June 13, 2007)
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Energetic costs of courtship signaling in two wolf spider species with divergent courtship behaviors |
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Authors |
Institutions |
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| Alan B. Cady | Department of Zoology,
Miami University Oxford, OH USA |
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| Kevin J. Delaney | Dept. of Land Resources and Environmental Sciences |
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| George W. Uetz | Department of Biological Sciences, University of Cincinnati Cincinnati, OH USA |
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Abstract: Active, complex display behaviors of males may provide information about male quality to females, and are considered to be “honest” indicators of male quality.As a consequence, females may prefer males capable of sustaining higher levels of energetically costly behavior. We measured energetic costs of courtship behavior for two sympatric wolf spiders [Schizocosa ocreata (Hentz) and S. rovneri (Uetz & Dondale)] which are reproductively isolated on the basis of differences in courtship behavior. These sibling species exhibit distinct courtship behaviors with different activity levels: S. ocreata uses multi-modal communication (visual and vibratory signals) and an actively moving courtship display, while S. rovneri uses only vibratory signals produced while stationary. Energetic expense (peak CO2 output) was recorded using a Sable Systems TR-2 flow-through respirometry system for spiders engaged in three behavioral activities: stationary, locomotion, and courtship behavior, and was found to vary significantly with species, individuals, and behavioral activity. No significant differences existed between species in peak CO2 output during stationary or locomotory behaviors, although these behaviors were significantly different within species. Courtship behavior of both species had significantly greater peak CO2 output than the other behaviors, and differences between species were significant. The active "jerky-tapping" courtship of S. ocreata produced higher peak CO2 levels than the stationary vibratory “abdomen bounce” display of S. rovneri. Differences in the energetic costs of courtship for these closely-related species may reflect the influence of sexual selection for different male signaling strategies. (posted June 15, 2007)
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Patch characteristics and population density in Geolycosa xera archboldi, a burrowing wolf spider narrowly endemic to Florida Scrub |
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Authors |
Institutions |
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James E. Carrel |
Division of Biological Sciences, University of Missouri-Columbia |
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Margaret A. Carrel |
Department of Geography |
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Abstract: Habitat fragmentation is considered a major threat to the persistence of many rare and endangered species. However, experimental studies of habitat fragmentation have shown both positive and negative effects on the density of populations in remnant habitat patches, reflecting autecological differences among species. We investigated the relationship between density of Geloycosa xera archboldi and the characteristics of patchy rosemary balds that it strongly prefers in native Florida Scrub. We used Akaike's Information Criterion (AIC) to evaluate the effectiveness of six a priori habitat models in predicting density of G. x. archboldi in rosemary balds. Only one model was strongly supported: there was a strong positive correlation between spider density and distance from a bald to the nearest sandy road or fire-lane. Other models (area of bald, shape complexity of bald, distance to nearest neighboring bald, time since last fire, and global) were not supported. Thus, contrary to our initial hypothesis, primitive roads and firelanes do not serve primarily as corridors of cursorial colonization; instead, they appear to be paths of emigration for spiders dispersing from balds. We wonder whether primitive roads and fire-lanes have a negative effect on G. x. archboldi density in Florida Scrub or, alternatively, if they may function effectively as highly linear "balds", thereby increasing the overall density of this narrowly endemic spider. (posted June 5, 2007)
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The costs and benefits of freezing in the presence of a predator in a Leiobuninae harvestman (Opiliones, Sclerosomatidae) |
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Authors |
Institutions |
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Marie-Claire Chelini |
Departamento de Zoologia, Instituto de Biociências, Universidade de São Paulo, São Paulo, SP, BRAZIL |
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Rodrigo H. Willemart |
School of Biological Sciences, University of Nebraska, |
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| Eileen A. Hebets | ||
Abstract: In this study, we aimed to determine the costs and benefits associated with a specific defensive behavior displayed by immature Leiobuninae harvestman from North America (Opiliones, Sclerosomatidae). Preliminary observations showed that immature individuals often become immobile (i.e."freeze") in the presence of the syntopic wolf spider Schizocosa ocreata (Araneae, Lycosidae). Harvestmen paired with spiders spent more time motionless than harvestmen alone or harvestmen paired with another harvestman. In order to determine if this immobility could decrease the likelihood of an attack by a spider, we examined the spider’s willingness to attack and eat motionless versus moving prey. Schizocosa ocreata individuals were paired with either living, and thus moving, crickets versus crickets that had been frozen to death and were thus motionless. Preliminary analyses suggest that the spiders took significantly longer to prey upon the motionless cricket than the live one. Some spiders never preyed upon the dead cricket, but readily ate a live cricket offered immediately after the trial. A third experiment allowed us to assess one potential cost of this defensive behavior. Harvestmen were paired with either a spider, another harvestmen, or nothing in arenas containing pieces of wet bread for 2 hours. Focal individuals were weighed immediately before and after the experiment. Individuals paired with spiders gained significantly less weight than individuals paired with other harvestmen or left alone. Our results suggest that the freezing behavior witnessed here may protect harvestmen from wolf spider attacks, but at the cost of reduced food/water intake. (posted June 7, 2007)
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Spectral properties, background matching and visual communication in the wolf spider, Schizocosa ocreata (Hentz) |
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Authors |
Institutions |
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| David L. Clark |
Department of Biology
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| Corinna Kizer | ||
| George W. Uetz | Department of Biological Sciences, University of Cincinnati |
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J. Andrew Roberts |
Department of E E O B |
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| Meghan Rector | ||
Abstract: Animal color patterns often evolve as a compromise between natural selection for crypsis and/or inconspicuousness to predators, and sexual selection for conspicuousness to potential mates. In leaf litter dwelling spider species like S. ocreata, body coloration often closely matches the background coloration of a generally brown environment. As a rule, however, body parts used in communication often contrast against background coloration. We used spectral analysis to examine male and female wolf spiders for matching and contrasting coloration against leaf litter. Values were plotted in multivariate color space, based on reflectivity in different frequency ranges. When viewed from above (top prosoma, top abdomen), both males and females overlap with values for leaf litter and soil, but not green plants, suggesting cryptic coloration when viewed by potential predators. However, when viewed from a lateral perspective (side prosoma, side abdomen) both males and females show values that are polar opposites of the backgrounds, suggesting higher contrast when viewed by other spiders. Moreover, male secondary characters (leg brushes) used in visual signaling by S. ocreata show the highest level of background contrast. We tested the hypothesis that visual displays and leg tufts are more conspicuous against complex leaf-litter backgrounds with video playback of courting males superimposed on backgrounds of natural leaf litter in sun vs. shade. Results suggest that complexity and light level of the leaf litter background affect potential detection of male visual signals by females, and that male foreleg tufts increase chances of detection (and subsequent receptivity) against this background. (posted June 5, 2007, updated July 7)
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Undersampling bias: the null hypothesis for singleton species in tropical arthropod surveys |
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Authors |
Institution |
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| Jonathan A. Coddington | Department of Entomology, National Museum of Natural History, Smithsonian Institution |
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| Ingi Agnarsson | Department of Biology, University of Akron |
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| Matjaz; Kuntner | Institute of Biology, Scientific Research Centre of the Slovenian Academy of Sciences and Arts |
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| Jeremy. A. Miller | Department of Entomology, California Academy of Sciences |
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| Gustavo Hormiga | Department of Biological Sciences, The George Washington University |
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Abstract: Singletons—species represented by single individuals—average 32% of large tropical arthropod surveys. We use a large but incomplete census of spiders in one hectare of lowland forest to test four common explanations for singleton frequency (patchiness, body size, sex ratio, cryptic habits) against a null hypothesis of undersampling bias. Singletons are larger than other species, are disproportionately female, share no particular life-style, and do not clump at 0.25-1 ha scales. Monte Carlo simulation of the best-fit lognormal community shows that the observed data fit a random sample from a community of ca. 700 species and 1-2 million individuals.Previous studies also failed to find a strong biological rationale for high singleton frequencies. We argue that undersampling bias should be the default null hypothesis for singleton frequencies. Undersampling causes systematic negative bias of species richness. Our data suggest that sampling intensities of 350-1100 specimens per species are sufficient for reliable species richness estimates using standard non-parametric methods; at 61.6, the average sampling intensity in large tropical arthropod surveys is severely inadequate. Methodological advances to increase estimator efficiency combined with raised expectations for sampling intensity in tropical arthropod inventory studies are called for if species richness estimates are to be credible; increased use of the lognormal may be part of the solution. (posted June 13, 2007)
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Spiders in Paint Creek, a local wetland: initial findings in family composition and distribution |
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Authors |
Institution |
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Laurie G. Cummins |
Eastern Michigan University, Department of Biology |
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| Cara Shillington | ||
Abstract: The presence of spiders in terrestrial ecosystems has been studied extensively. Little is known, however, about the role of spiders in aquatic ecosystems, especially wetlands. The purpose of this study was to obtain a preliminary understanding of the spider community found in a local wetland, Paint Creek. Aerial and ground samples were collected along a 50-meter transect in a dense stand of native Typha latifolia. Samples were taken monthly from May to September, and were analyzed for both family composition and plant biomass. Initial findings indicate that spider communities in wetlands are highly variable. Ground samples yielded the largest number of individuals, high plant biomass yielded a diverse composition of spiders, and all variables changed with season. Overall, the family Lycosidae exhibited the highest abundance, followed by Clubionidae. Unexpectedly, the family Tetragnathidae exhibited the least number of individuals collected over the 5 month period. Continued sampling is needed to further understand the complex dynamics of spider communities in wetland habitats. (posted June 5, 2007)
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Global survey and inventory of Solifugae |
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Authors |
Institutions |
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Paula E. Cushing |
Department of Zoology |
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Lorenzo Prendini |
Division of Invertebrate Zoology |
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Warren E. Savary |
Department of Entomology |
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John O. Brookhart |
Department of Zoology |
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Robert A. Wharton |
Department of Entomology |
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Tharina Bird |
Department of Zoology |
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Alexander V. Gromov |
Laboratory of Entomology |
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Abstract: Solifugae, the sixth most diverse order of arachnids, are dominant predators in arid ecosystems on all major terrestrial land masses except Antarctica, Australia, Madagascar and New Zealand. Despite their diversity, worldwide distribution, ecological importance, and remarkable morphology, behavior and life history, research on these fascinating arachnids has advanced little in 50 years. Many aspects of their biology remain unknown, fewer than ten researchers worldwide are presently studying any aspect of their biology, and publications on the group currently average only five per year. Given the paucity of active specialists, the situation will not improve until more are trained. Research is further hindered by a limited application of modern concepts and methods. The Global Survey and Inventory of Solifugae (http://www.solpugid.com), funded by the Biodiversity Surveys and Inventories program of the U.S. National Science Foundation, aims to reverse these negative trends and stimulate research on Solifugae as follows. (1) Fieldwork will be conducted in 13 countries in four regions of greatest known diversity to discover new species, document distributions, and gather fresh material for morphological, anatomical, behavioral and genetic studies. (2) The higher classification will be revised based on phylogenetic analysis. (3) Monographs on large monophyletic groups (three family-scale revisions) will be published. (4) Rigorous standards and modern techniques will be employed in research. (5) Collaborations will be forged among specialists currently working largely in isolation, and resources provided to expand their research. (6) New experts will be trained in traditional techniques as well as modern concepts and methods. (7) Results will be disseminated to the public via the internet. This project to resuscitate solifuge research, coordinated in North America but involving the world's solifuge specialists and arachnologists interested in diverse aspects of solifuge research in 17 countries, will invigorate solifuge research worldwide.. (posted June 1, 2007)
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Galvanizing your specimens: unintended consequences of using green neoprene stoppers in alcohol based collections |
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Author |
Institution |
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| Bruce Cutler | Microscopy & Analytical Imaging Laboratory and Department of Ecology & Evolutionary Biology |
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Abstract: During an ongoing investigation of heavy metal occurrence in spider cuticle a few ethanol stored specimens showed anomalous zinc distribution. This was eventually traced to specimens stored in vials with green neoprene stoppers. Ethanol from vials with just a few years exposure to green stoppers contained zinc. Ethanol from vials stoppered with other common closures, including black, red and white rubber stoppers lacked zinc, even over an estimated time of several decades. Zinc salts, especially the oxide, are present in most rubber products since they are used as curing and filling agents, however only green stoppers appear to leach zinc into the ethanol. The overall effect of this zinc deposition on the specimens is uncertain. Zinc does have some antimicrobial properties so perhaps it could inhibit specimen decay. On the other hand, it can interfere with chemical analysis as in this instance, and possibly could interfere with other types of analysis. (posted May 31, 2007)
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Cape Cod spiders and their habitats |
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Author |
Institution |
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Robert L. Edwards |
Northeast Center Director, NOAA. Retired. |
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Abstract: During WWII and for some years afterwards, large tracts of agricultural land were abandoned. Subsequently, depending on the land use history, large acreages were left to develop on their own. Today there are a wide variety of sizable blocks of relatively uniform habitats. These have been sampled since 1990, larely by myself with some assistance in the field in upland areas. Particular attention is paid to comparing differences in species composition, and relative abundance in 11 different habitats when comparing numbers and weight of spiders. Whether looking at weight or number, the degree of relationship is evident. In this area two coniferous trees are particularly aggressive pioneers - Red Cedar (Junperus virginiana L. and Pitch Pine (Pinus rigida Mill. A third large block of introduced Norway Spruce (Picea abies L. ) is also present. The effect of structure on the species composition is clearly evident. 'Hockey Stick' plots are useful for getting a first impression of which species constitute that set that dominates the population. They may be computed on the basis of average number/quadrat, total numbers or even weigh. Various approaches provide different insights and suggests further means of analysis, when comparing seasons for example. (posted June 19, 2007; modified 2 July)
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Origins of Synsphyronus (Pseudoscorpiones) diversity on the outcrops of southwestern Australia |
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Authors |
Institutions |
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| R.S. Engel | University of Connecticut |
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| E.L. Jockusch | ||
M.S. Harvey |
Department of Terrestrial Invertebrates, Western Australian Museum |
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Abstract: Pseudoscorpions are found in a variety of habitats worldwide yet this arachnid order with at least 3300 species remains understudied. The genus Synsphyronus Chamberlin comprises 28 described species found in Australia and New Zealand. One region where this clade’s diversity has not been fully documented is southwestern Australia, an ancient landscape noted for its floristic richness and granite outcrops. The granite outcrops form terrestrial habitat islands, refugia for isolated populations of outcrop-endemic biota including Synsphyronus. S. elegans was the sole described outcrop-endemic in this region, known only from the type locality, but recently two new morphospecies were collected from an outcrop 50 km away. This project aims 1) to characterize the diversity and evolutionary relationships of Synsphyronus endemic to the outcrops in southwestern Australia and 2) to elucidate the evolutionary origins of the outcrop-endemic lineages of Synsphyronus by reconstructing a genus-level molecular phylogeny. Specifically, we are testing the hypothesis that there are multiple origins of outcrop lineages. DNA sequence data provide a useful way to infer relationships as these pseudoscorpions are morphologically cryptic and exhibit high levels of homoplasy. The 70 populations we have sampled within a ~35,000 km2 region sort into five morphospecies, which includes two described species. Data from cytochrome oxidase subunit I and internal transcribed spacer region indicate that these outcrop taxa are not monophyletic, but instead form four deeply differentiated lineages which largely correspond to four morphospecies. These data are consistent with the hypothesis that there have been multiple origins of outcrop lineages in southwestern Australia. (posted June 18, 2007)
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Examining the enzymatic action of select spider venoms on the phospholipids of sheep red blood cell ghosts |
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Authors |
Institutions |
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| Matthew J. Foradori | Department of Biology and Health Services |
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| Elizabeth Smith | Department of Animal and Nutritional Sciences |
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| Samuel C. Smith | ||
Edward K. Tillinghast |
Department of Zoology |
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Abstract: It has proven difficult to identify those spiders which cause necrotic lesions. Aside from Loxosceles reclusa, conflicting reports from case studies and reviews have only managed to make identification of potentially medically significant spiders more confusing. In an attempt to clarify the medical significance of some of the spiders, we embarked on a survey of over 45 spider species venoms for there potential to cause hemolysis. Along with the known hemolytic activity of L. reclusa venom, we found the venom of Cheiracanthiummildei to be hemolytic as well. As an extension of that research, our lab examined the ability of select spider venoms to cleave phospholipids present in the membranes of sheep erythrocytes. Hemoglobin-depleted red blood cell ghosts were challenged with venom gland homogenates from Argiope aurantia, Phidippus audax, Latrodectus geometricus, C. mildei or L. reclusa for three hours at 37º C. The results suggest that the venom of C. mildei contains a phospholipase A2. However, even more interesting was the presence of phospholipase activity in the venom of L. reclusa, which along with sphingomyelinase D, cleaved most of phospholipids in the red blood cell ghosts. (posted June 5, 2007)
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Behavioral responses to the threat of predation in a mixed population of brush-legged and non-ornamented wolf spiders |
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Authors |
Institution |
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| Kasey D. Fowler-Finn | School of Biological Sciences |
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| Eileen A. Hebets | ||
Abstract: In a recently discovered population of Schizocosa wolf spiders, we find individuals comprised of two adult male forms, each with unique morphology and courtship displays - a non-ornamented form with a seismic only courtship signal and a brush-legged form with unique seismic and elaborate visual signals. Preliminary microsatellite data reveal no genetic distinction between these two male forms and thus the question remains as to what is maintaining the presence of both forms. Though brush-legged males are putatively more conspicuous, previous field studies showed no differences in over-all rates of predation on the two male forms. However, a measure of over-all predation rate can mask potential form-specific differences in predation risk, anti-predator behavior and/or predator-prey interactions. Here we conducted controlled laboratory experiments to investigate the details of anti-predator responses. We first compared the responses of each male form to predator silk and excreta cues. Overall movement time and likelihood of courtship was significantly greater in the absence of predator silk cues for both male forms but we found no form-specific differences. In a second experiment, we used live predator-prey interactions with a larger predatory wolf spider to examine the latency to and number of survived attacks. Again, we found no differences between the brush-legged and non-ornamented males for the latency to the first attack, the number of survived attacks, the latency to capture or capture rate. These experiments, in conjunction with our previous field study, suggest that there are no differential costs associated with predation from larger predatory wolf spiders between brush-legged and non-ornamented males from this mixed population. (posted June 19, 2007)
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A comparison of the courtship behaviors of the funnel-web spiders Barronopsis texana, Agelenopsis emertoni and Agelenopsis aperta |
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Authors |
Institution |
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| Audra B. Galasso | Department of Ecology and Evolutionary Biology |
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| Susan E. Riechert | ||
Abstract: Comparisons of sexual behavior among closely related species may elucidate phylogenetic relationships or may perhaps reveal strong sexual selection. The courtship of one Agelenopsis species, A. aperta, has been previously described in detail. Here we describe the courtship of another species in the genus, A. emertoni, as well as the courtship of a member of its sister genus, B. texana. Similar behaviors are observed in all three species, but the temporal patterning and frequencies of these behaviors differ. These differences and differences in overall activity level are described and discussed in light of phylogeny. (posted June 19, 2007)
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Do male Schizocosa ocreata (Hentz) wolf spiders respond to other courting males? |
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Authors |
Institutions |
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| Emily Galbraith | Dept. of Biological Sciences |
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| Jenai Milliser | ||
| George W. Uetz | ||
| Corinna Kizer | Dept. of Biology, Alma College |
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| David L. Clark | ||
| J. Andrew Roberts | Dept. of EEOB, Ohio State University Newark |
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Abstract: Selection on males to locate females before other males may favor exploiting mate-searching efforts of others by “eavesdropping” on courting males. Male Schizocosa ocreata (Hentz) wolf spiders spend a large portion of their time searching for potential mates within complex forest leaf-litter, frequently courting in response to female silk draglines. Previous studies using both live males and video playback suggest that males do not exhibit social facilitation of courtship (i.e., respond to the courtship of others with increased courtship after exposure). However, these studies used males reared in isolation. Given that males occur in high densities in nature, it seems likely they encounter courting conspecifics often during the mating season. In this study, we test the hypothesis that prior experience and exposure in the field impacts the tendency of male S. ocreata wolf spiders to eavesdrop on conspecific males. Video playback studies with field-collected males demonstrated behavior consistent with eavesdropping, i.e. increased following and courtship behavior during and after exposure to a courting male stimulus. Studies also showed that when presented with two male video stimuli simultaneously, males interact more with images of courting males than of males walking on screen and spent more time in courtship display activity in proximity to the courting male video stimulus than the walking male. Follow-up studies using live spiders were more equivocal, and do not fully corroborate video results. While some of these results suggest experience may play a role in male behavior, it is at present unclear to what extent eavesdropping occurs. (posted June 19, 2007)
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Investigation of decision-making and transitivity of preferences in female choice of Schizocosa ocreata (Hentz) (Araneae: Lycosidae) |
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Authors |
Institutions |
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Emily L. Galbraith |
Dept. of Biological Sciences University of Cincinnati Cincinnati, Ohio USA |
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George Uetz |
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| Stephanie Norton | ||
| J. Andrew Roberts | Department of Evolution, Ecology and Organismal Biology |
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Abstract: When females evaluate potential mates, they may assess males using multiple criteria, and selection is expected to favor females that choose males based on increasing indicator trait quality, i.e., a fixed hierarchy of choices known as “transitive preferences". However, male characteristics may differ in the information they provide to females. In settings where multiple male traits are varied, females may weigh characteristics differentially and as a result violate hierarchical preferences, ultimately displaying what is known as “intransitivity". We studied decision-making in mate choice by female Schizocosa ocreata (Hentz) wolf spiders by testing hypotheses about transitivity of preferences for multiple criteria, including foreleg tuft size and courtship display rate, both of which may indicate male quality, but reflect success/fitness at different life stages. We used video digitization and playback techniques to modify male traits, and presented them to females in simultaneous choice combinations in a repeated-measures design. Females appear to exhibit transitive preferences for male signaling characters, but may display intransitivity in mate choice. This violation of expected hierarchies of preference may suggest a level of cognitive complexity through comparative evaluation of alternatives, rather than using fixed scales of measurement. Results suggest that some decision-making models of mate choice, which assume the use of fixed scales, may be inaccurate. Results will be discussed in the context of recent research on invertebrates that reveals previously unrecognized levels of flexibility and cognitive complexity in foraging and reproductive behavior. (posted June 5, 2007)
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Microbial fauna associated with the medically implicated hobo spider, Tegenaria agrestis, in the U.S. Pacific Northwest and their likelihood of causing infectious lesions |
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Author |
Institution |
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| Melissa M. Gaver | Department of Entomology, Washington State University |
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Abstract: In the Pacific Northwest (PNW), the hobo spider, Tegenaria agrestis, has been implicated as a spider of medical concern because the bite is thought to cause necrotic lesions. The hobo spider has rapidly expanded its range since its introduction into the PNW in the 1930's and has moved into neighboring states beyond the PNW. Although there are no verified published accounts, the hobo spider continues to be named as the causative agent for necrotic or infected lesions of unknown origin. Venom analysis does not show any known components that would induce tissue necrosis and the spider is not a medical concern in Europe, the originating country. Recent publications link necrotic lesions to a bacterial infection yet, the spider is still popularly considered as a bacterial vector although there is no evidence to substantiate this idea.Therefore, the next step in verifying the toxicity of the hobo spider bite is to identify the microbial fauna associated with this spider in order to establish whether or not there are pathogenic bacteria associated it. Exciting advances in molecular biology have introduced new tools that are available to determine bacterial biodiversity. Universal bacterial primers have become available to identify bacteria found in natural environments, some which are medically important. An ongoing examination the microbial fauna found on the medically implicated spider Tegenaria agrestis has begun using universal bacterial primers, 63f and 1389r for the polymerase chain reaction (PCR) amplification of 16S r RNA genes. (posted June 1, 2007)
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Biological organization of molting in the scorpion Heterometrus swammardami |
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Author |
Institution |
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| Mohammad Habibulla | Schaumburg Township Human Services |
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Abstract: Although a lot is known about molting in insects, it is regrettable that we know very little concerning it, in the case of arachnids, especially in the scorpions. Our long-term study of the scorpion Heterometrus swammerdami has revealed interesting information in this archaic group. Structurally and functionally, in many respects, the biological organization of molting is different in this scorpion. This difference reflects in the fact that in the scorpion there are only a series of molts without metamorphosis resulting in physical growth and sexual maturity. Protocerebral neurosecretory cells, leucocytes, and the ‘blind end organ’ the rostral organ, the hypocerebral ganglion and the frontal ganglion are some of the structures intimately connected functionally. Neurosecretory effectors from the brain, effector’s following systems, signaling messaging devices, and some feedback mechanisms shall be discussed in the presentation. (posted June 7, 2007)
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Preferences of novel and known prey types of the tarantula Phormictopus cancerides |
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Authors |
Institution |
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| Ryan Harper | Department of Biology |
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| Brandon Neel | ||
| Sharif Shahin | ||
| Cara Shillington | ||
Abstract: As sit-and-wait predators, tarantulas are opportunistic carnivores that rapidly attack and subdue a wide variety of prey moving within close proximity to their burrows or retreats. However, in a laboratory environment, captive-bred and raised tarantulas are more likely to have limited exposure to different prey. We examined prey capture and feeding behaviors of Phormictopus cancerides (Araneae: Theraphosidae) raised on a combination of both crickets and waxworms (Group 1) or crickets alone (Group 2). During feeding experiments individuals from these groups were offered waxworms, crickets, and cockroaches in separate trials. Thus, both groups were exposed to both novel and known prey items. We recorded feeding behaviors associated with each prey type including: 1) first movement towards prey; 2) first contact with prey; and 3) capture time. Within both groups, crickets were captured the quickest, often with no prior contact. Group 1, took the longest time to capture waxworms even though they had been fed waxworms prior to the start of trials. Differences in prey behavior and movement influences tarantula activity. Specific prey-handling behaviors associated with capture of novel and known prey are described in detail in the abstract by Shahin et al. (posted June 19, 2007)
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Are you paying attention? Female wolf spiders increase silk deposition when males don’t court |
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Authors |
Institutions |
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| Jamie Havrilak | Biology Department, Susquehanna University |
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| Kristen Shimmel | ||
| Ann L. Rypstra | Department of Zoology, Miami University |
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Matthew H. Persons |
Biology Department, Susquehanna University |
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Abstract: Female spiders use silk to advertise their receptivity to mate but little is known about variation in investment in silk to attract males or the context in which it is deposited. We measured variation in the quantity and type of silk deposited by virgin females of the wolf spider, Pardosa milvina, in the presence or absence of males and among males that varied in their courtship intensity.We measured total female silk deposition, cord silk deposition, and attachment disk deposition on gridded sheets of paper in response to one of four treatments: 1) an intensively courting male with access to female silk, 2) a weakly courting or non-courting male without access to female silk, 3) no male, but female silk present, and 4) no stimulus (control). Unmated females were placed under transparent petri dishes on paper grids within the centers of larger circular arenas. If males were present they were permitted to move about in the larger circle surrounding the female but had no direct access to the female for 30 minutes. After the trial period, the types of silk deposited on the grids were quantified. Females produced significantly more total silk in the presence of non-courting or weakly courting males but produced significantly less cord silk among non-courting or weakly courting males. We found no significant difference in attachment disk deposition across any treatments. Our results suggest that females invest more heavily in dragline deposition when encountering non-courting males and mediate their advertising investment based on male behavior. (posted June 7, 2007)
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I’m just not into you: Using forced mating experiments to untangle male and female mate choice in the wolf spider Pardosa milvina |
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Authors |
Institution |
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| Jamie Havrilak | Biology Department, Susquehanna University |
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| Abraham Taylor | ||
Matthew H. Persons |
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Abstract: Female mate choice is often measured as receptive responses of females toward males and/or actual mating. However it is often difficult to determine if female choice is also driven by males choosing to show reduced courtship or interest in females because of male mate choice acting simultaneously. We sought to separate the relative contributions of male mate choice and female mate choice in determining mating success. We measured variation in courtship rates and duration among males that elicited female receptivity compared to those that did not. Then, using carbon dioxide we anesthetized females and paired them with either males they formerly accepted as mates or males that did not elicit female receptive responses. To measure copulatory efficiency and competency, we then measured the number of insertions, insertion rate, and missed insertions among force-mated females. We also measured egg sac production of females that force-mated with formerly accepted versus rejected males compared to control matings with unanesthetized females. Males that formerly failed to elicit receptive responses in females were significantly less likely to mount anesthetized females, suggesting that male mate choice may be involved in mating failures. Among formerly rejected males that did mate with anesthetized females, the insertion rate and number of missed insertions were no different than that of previously accepted males suggesting that once mounted, females do not modify their copulatory behavior toward previously rejected males and females don’t choose males based on copulatory competence. Eggsac production was the same among formerly rejected and accepted force-mated females. (posted June 7, 2007)
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Shifting metabolic needs during development: The proximal path to giant females |
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Authors |
Institution |
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| Linden Higgins | Department of Biology, University of Vermont |
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| Charles Goodnight | ||
Abstract: Nephila clavipes life history has two widely known attributes: extreme sexual size dimorphism, and highly variable but exceedingly large female body size. In an effort to determine how much of the variation in body size is caused by food availability, we designed a common garden experiment subjecting juveniles to low, medium, or high food levels (45%, 56% or 84% mean post-molt mass in live prey/week) starting with dispersal (3rd instar). Males and females responded differently to the experimental diets: nearly all males reached sexual maturity by the fifth instar. Male size at maturity varied with diet, but total developmental time did not. For females, these diet levels were sufficient for normal development only until the sixth instar, at which time they ceased growing. We found that an increase of 50% in food levels restored development, allowing surviving individuals to reach maturity. In females, both size and total developmental time varied with diet. We compare these data to an ongoing experiment where all individuals are shifted to the higher food levels in the beginning of the 6th instar. (posted May 30, 2007)
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Ontogenetic and sex-specific differences in dragline and excreta deposition in the wolf spider Pardosa milvina |
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Authors |
Institution |
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| Rebecca Holler | Biology Department, Susquehanna University |
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| Christopher Latanich | ||
Matthew H. Persons |
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Abstract: Dragline deposition is common among most spiders but variation in silk production based on the age, sex, and reproductive status of spiders remains unclear for cursorial spiders. We measured the quantity and type of silk and excreta deposited in the wolf spider Pardosa milvina. We compared differences in silk and excreta deposition as a function of sex, developmental stage (penultimate instar versus mature), mating status (virgin or mated), and female reproductive status (eggsac or no eggsac). Field-collected Pardosa were allowed to move freely for four hours on individual grid-bearing 80 mm dia. paper disks. We then quantified cord silk and fine-gauge dragline silk coverage, number of attachment disks, and excreta produced on each sheet. Cord silk deposition did not vary across any group. We found significant differences in attachment disk deposition with adult females with eggsacs producing none, adult and subadult males producing very low levels, and adult mated females producing more than virgin females. Total silk deposition was significantly lower among eggsac-carrying females and highest among females immediately collected from the field. Surprisingly, we found no significant difference in silk deposition between mated and virgin females nor between adult males and unmated females. Eggsac carrying affects attachment and fine-gauge silk deposition but has little impact on cord silk. Excreta deposition showed significant differences between groups with adult virgin females and adult males producing the most and adult females with eggsacs the least. This suggests reduced feeding among eggsac-carrying females and high feeding rates among unmated females and adult males. (posted June 7, 2007)
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Once bitten, twice shy? Aggressive male mating behavior and fang use in the brush-legged wolf spider Schizocosa, ocreata |
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Authors |
Institutions |
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Julianna L. Johns |
University of Cincinnati |
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| George W. Uetz | ||
J. Andrew Roberts |
Department of Evolution, Ecology, and Organismal Biology |
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Abstract: Where sexually receptive females are limited, sexual selection is driven by increased competition between males and/or the degree of female choosiness. This may result in sexual conflicts of interest between males and females. Under these circumstances, increased selection pressure on males can result in aggressive and/or coercive male mating behaviors to counter female choosiness and/or resistance. In S. ocreata, males exhibit elaborate courtship displays, but even when females are not receptive, mounting and subsequent copulation sometimes occur. Analysis of mating trials indicates an apparent rate of 12.7% coercive mating and forced copulation. Principal Component Analysis revealed distinct behavioral patterns associated with outcome of coercive vs. cooperative mating trials. While most pairings included male courtship and receptivity displays by females before mating, we found decreased receptivity and increased resistance to aggressive males by females in coercive matings. Adult male S. ocreata have been observed to use fangs during copulation, resulting in hemolymph loss and scarring in females. We experimentally immobilized male fangs and compared mating success between manipulated and control (sham manipulated) groups. Although there was no difference between groups in mating success, we found reduced copulation duration time for those males unable to use their fangs. Preliminary analysis suggests no increase in reproductive success associated with copulation duration time or fang use, although males who mate coercively may gain potential fitness benefits from reduced courtship cost. The role of coercive mating as a reproductive tactic in S. ocreata will be discussed. (posted June 13, 2007)
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Patterns of reproductive success associated with social structure and microclimate in Anelosimus studiosus (Araneidae, Theridiidae) |
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Authors |
Institutions |
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Thomas C. Jones |
Department of Biological Sciences, East Tennessee State University |
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Susan E. Riechert |
Department of Ecology and Evolutionary Biology |
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Abstract: In east Tennessee, the Theridiid spider Anelosimus studiosus varies widely in its social structure from the solitary/territorial female with her offspring, to cooperative colonies of tens to hundreds of adult females. In previous work, we developed a brood fostering model that predicts that in cooler environments mothers in multiple-female colonies will have a selective advantage over solitary female nests. This is because the rate of juvenile maturation is slowed and the mother has a higher probability of dying before the brood reaches independence. In her absence, other females would foster her brood. We tested this hypothesis by manipulating colony size and by monitoring the reproductive success of naturally occurring solitary- and multi-female colonies in cold and warm temperature environments. Our results indicate that while multiple-female colonies have higher fitness at cool sites, the solitary female nests achieve higher fitness at warmer sites. The higher reproductive success of multi-female colonies at cold sites further reflects the total failure of solitary female nests at these sites. Surviving solitary female nests generally had higher reproductive success than multi-female colonies. In natural colonies, fitness is highest for smaller multi-female colonies in the colder environments, and decreases in the larger colonies. We use these data to refine the brood-fostering model and discuss the results with regard to the observed polymorphism in social structure. (posted June 11, 2007)
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The benefits and costs of group courtship in the sexually cannibalistic species Dolomedes triton |
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Authors |
Institution |
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| Nancy A. Kreiter | Department of Biology |
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| Virginia L. Weeks | ||
Abstract: Predatory females place constraints on male courtship in sexually cannibalistic species. For example, courting in groups may increase competition for mating opportunities, but it also can reduce an individual male’s likelihood of being cannibalized. Small groups of male Dolomedes triton have been observed in the field simultaneously exhibiting courtship; participation in such group courtship may represent a tradeoff between safety and mating success. Laboratory tests of this hypothesis were conducted using newly molted adult females paired with either a single male (n=24) or two males (n=26). Field-caught juvenile spiders were allowed to mature in the laboratory. Males were tested in both conditions (singly and with another male), with order of the trials randomly assigned. The presence of other males did not result in significant benefits or costs to males. Cannibalism rates were not statistically different for single males (12.5%) and focal males in 2-male trials (7.7%), and the presence of a competitor did not cost males in lost inseminations. Single males mated in 37.5% of trials, while focal males in 2-male trials mated in 31% of trials. Females, however, derived many benefits from having two males present. They were more likely to mate if two males (54%), rather than one male (37.5%), were present and were almost twice as likely to cannibalize if two males were present (23%) than one (12.5%). Group courtship in D. triton may not reflect male strategies for reducing cannibalism, but may instead represent a mechanism for female choice in this species. (posted June 19, 2007)
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Effects of structural complexity and habitat switching upon the development of silk deposition behaviors in the wolf spider Hogna helluo |
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Authors |
Institutions |
| Christopher A. Latanich | Biology Department, Susquehanna University |
| Michelle M. Smith | |
| Rebecca L. Holler | |
Ann L. Rypstra |
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