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Henry Wilbur, Robert Jaeger and Caitlin Gabor

Abstract

We conducted behavioral experiments to determine how competition and predation may affect an assemblage of salamanders that meet at and cross forest to aquatic ecotones. At Mountain Lake Biological Station, southwestern Virginia, USA, adults of four abundant species interact at the forest to stream ecotone. Plethodon einereus and the larger P. glutinosus inhabit the forest floor up to the edges of streams while Desmognathus fuscus and Eurycea eirrigera forage from the edges of streams onto the forest floor. Our six laboratory experiments yielded predictions as to how these species affect each others' distributions and abundances in the natural habitats. Previous studies showed that adults of P. cine reus are territorial intraspecifically and toward same-size juveniles of P. glutinosus. In our experiment, territorial residents of P. einereus did not act aggressively toward intruding adults of P. glutinosus and the latter species was neither aggressive nor predatory toward P. einereus. The two species were equally benign in a second experiment when the roles of resident and intruder were reversed. Thus, we predict that the adults of these two species do not influence each others' distributions on the forest floor.

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Caitlin R. Gabor, Caitlin R. Gabor, Jaime Bosch, Caitlin R. Gabor, Jaime Bosch, Joe N. Fries, Caitlin R. Gabor, Jaime Bosch, Joe N. Fries and Drew R. Davis

Anthropogenic disturbances have been implicated in the rapid decline of amphibians. Disturbances, such as disease and poor water quality, might cause changes in the physiology of amphibians resulting in chronic stress, which can result in decreased growth and development as well as immunosuppression. In amphibians, corticosterone (CORT) is the main hormone released in response to stressors. We took the first steps towards validating a new, non-invasive, technique to assay CORT in amphibians using a water-borne collection method previously used only with fish. In validation of this technique, we found a significant positive correlation between release rates of water-borne CORT and levels of CORT in circulating plasma in adults of the San Marcos salamander, Eurycea nana, and the common midwife toad, Alytes obstetricans. These results indicate that water-borne CORT can be used as a proxy for plasma CORT. Additionally, we examined basic background information on the physiological states of these two species. We found that captive-reared salamanders had significantly lower release rates of CORT than field-collected salamanders. Field-collected salamanders had significantly higher CORT release rates 24 h after capture and transfer to the laboratory. For tadpoles, we found that field-collected tadpoles did not have significantly different CORT release rates than those maintained in the laboratory for four months. Our research indicates that this method of water-borne hormone collection should be viable for many species of amphibians; however, further validation via adrenocorticotropic hormone (ACTH) challenges is required. This method can be a useful tool for assessing the physiological state of laboratory and field populations of amphibians and the effects of urbanization, pesticides and diseases. An important benefit of this method is that it allows for repeated measures of the same individuals and can be less stressful than drawing blood.

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Caitlin Gabor, Julia Coyle and Andrea Aspbury

Abstract

Mate choice for conspecifics is beneficial when closely related species live in sympatry, but mate choice can be costly in the presence of predators. Male sailfin mollies are sexually parasitized by gynogenetic Amazon mollies. Amazon mollies must mate with male sailfin mollies to initiate embryogenesis, but inheritance is maternal. We tested if male sailfin molly mate choice for conspecific females is affected by predation risk. Male mate choice was tested in one of four treatments: (1) predation/no refuge, (2) predation/refuge, (3) no predation/refuge and (4) no predation/no refuge. Predation consisted of dipping the beak of a great blue heron decoy in the aquarium prior to a mating trial. Refuge was provided by java-moss. For each trial the number of mating attempts toward each female was recorded. There was a significant interaction between predation and refuge on strength of preference (SOP) for conspecific females. The highest SOP was in the no predator/no refuge treatment, and the lowest SOP was in the predator/no refuge treatment. These results suggest that the cost of predation is higher than the cost of mating with heterospecifics, and that the presence of a refuge may reduce this cost. This could explain the continued maintenance of Amazon mollies.

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Caitlin Rathie Gabor, Reynaldo Gonzales Jr. and Kristen Joy Epp

Abstract

Association patterns and social interactions of salamanders vary given habitat heterogeneity and behavioural characteristics. Cave ecosystems are generally food limited and encountering mates may be rare. Little is known about the mode of social interactions and preferences in cave-adapted salamanders. We examined social interactions of the caveadapted, federally endangered, Texas blind salamander, Eurycea rathbuni, by examining sex-specific association patterns. We predicted that non-visual (chemical) cues would be an important mode of communication. We found no difference in association patterns between the sexes when presented with a single conspecific and no aggregative behaviours were detected. Interestingly, when given a simultaneous choice between a male or female, females preferred to associate with male conspecifics while males showed no clear preference. The results suggest that females of E. rathbuni use chemical cues to either seek males or avoid females and provide valuable insight into the little known social behaviour of this species and possibly other similar species.

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Maria Thaker, Caitlin Gabor, Joe Fries and Kristen Epp

Abstract

Social interactions of conspecifics are a function of complex relationships involving resource defense, antipredatory tactics, and mate acquisition. Consequently, individuals often associate non-randomly with conspecifics in their habitats, with spatial distributions of adults ranging from territorial spacing to aggregations. Site tenacity and cohabitation patterns have been well studied in many species of terrestrial salamander; however, less is understood about these behaviors in aquatic species. We examined the cohabitation patterns of intrasexual and intersexual pairs of the federally threatened, paedomorphic San Marcos salamander (Eurycea nana) under artificial shelters in a laboratory setting over a 20-day period. We found that intrasexual female pairs and intersexual pairs were found cohabiting more often than intrasexual male pairs. We also assessed site tenacity by examining shelter affinity and found that both males and females inhabited one of the two shelters more often than expected from random habitation, regardless of whether they were in intersexual or intrasexual pairings. Our results indicate that although both sexes of Eurycea nana exhibit site affinity, the sex of individuals is an important determinant of cohabitation patterns.

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Laura Alberici da Barbiano, Caitlin R. Gabor, Andrea S. Aspbury and Lorena Rangel

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Caitlin Gabor, Zachery Forsburg, Judit Vörös, Celia Serrano-Laguna and Jaime Bosch

Batrachochytrium dendrobatidis (Bd) causes the disease chytridiomycosis associated with amphibian declines. Response and costs of infection varies greatly between species. Bd can induce a stress response in amphibians resulting in elevated corticosterone (CORT). We exposed Bombina variegata and Hyla arborea tadpoles to Bd+ or Bd- Salamandra salamandra larvae and measured CORT release rates, Bd infection loads, and survival through metamorphosis. Tadpoles of both species exposed to Bd+ larvae had elevated CORT release rates compared to tadpoles exposed to Bd- larvae. Bombina variegata appear less resistant to infection than H. arborea, showing higher Bd loads and more infected individuals. Within species, we did not find differences in cost of infection on survival, however more B. variegata tadpoles reached metamorphosis than H. arborea. The differences in resistance may be species specific, owing to higher immunity defenses with H. arborea having higher overall CORT release rates, and differences in antimicrobial peptides, or to differences in Bd strain or other unexplored mechanisms.