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    Session 40: Herpetology Physiology

    Room: Room 206D

    2022-07-30   13:30 - 16:00

    Moderator: Brad Carlson



    1.  13:30  Color, Behavior, and Stress Physiology are not linked in Box Turtles. Bradley Carlson*, Wabash College; William Robinson, Wabash College   carlsonb@wabash.edu

    Endocrine systems, individual behavioral differences (temperament), and melanin-based coloration are often linked in animals. In particular, glucocorticoid (“stress”) hormone levels are often lower and melanin amounts higher in individuals that exhibit more proactive behavior. The “melanocortin hypothesis” proposes that variation in the melanocortin system could drive this covariation in coloration, behavior, and glucocorticoid levels. We evaluated the relationships among the stress-induced corticosterone (CORT, a glucocorticoid), boldness (i.e., responsiveness to risk), and melanization of the shell in Eastern Box Turtles (Terrapene carolina carolina), predicting that turtles with bolder temperaments would exhibit lower stress-induced CORT levels and possess darker shells. Our results failed to support the melanocortin hypothesis, as we found weak and non-significant correlations among behavior, CORT, and melanization. Interestingly, we also found that temperature had a strong positive effect on CORT levels, and there were population differences in plastron melanization and boldness.


    2.  13:45  Glucocorticoids, Sex Steroids, and Innate Immunity, Oh My!: Examining Reproductive Investment and Physiological Tradeoffs in a Freshwater Turtle. Jennifer Terry*, Arkansas State University; Emily Field, Arkansas State University; Lorin Neuman-Lee, Arkansas State University   jennifer.terry@smail.astate.edu

    Reproductive processes are expected to be costly and dynamic. Organisms may accommodate for heightened reproductive investment through physiological tradeoffs. We investigated circulating glucocorticoid and sex steroid concentrations and innate immune function in wild adult red-eared sliders (Trachemys scripta) between May–October 2019 in Northeast Arkansas, USA. We subjected animals to an acute stressor by removal from a net or hand capture and collected blood samples 0–3, 30, and 60 minutes after removal. We used thawed plasma in bacterial killing assays (BKA) to measure innate immune function and radioimmunoassays to measure corticosterone (CORT), testosterone (T), estradiol (E2), and progesterone (P4) concentrations. We compared each response variable by month and BKA/CORT by bleed time within month separately by sex. Female red-eared sliders have increased concentrations of CORT and P4 while developing multiple clutches simultaneously and decreases in innate immune function occurred during reproduction. In males, low innate immune function in May suggests that tradeoffs between innate immunity and Spring mating effort may be present. Further, male red-eared sliders had higher T, CORT, and innate immune function in August, which may be in preparation of spermatogenesis and Fall mating effort. This study indicates that reproductive investment is dynamic within the reproductive period and varies by sex in native red-eared sliders. Further, by determining how these abundant reptiles invest energy during obligatory processes, such as reproduction, we can better address questions within the fields of conservation and comparative ecophysiology.


    3.  14:00  Effects of Shifting Temperatures During Early Incubation on Embryonic Development and Growth in Chelydra serpentina. Michael Finkler*, Indiana University Kokomo; Andrew Pervez, Indiana University Kokomo   mfinkler@iu.edu

    In higher latitudes within their range, snapping turtle eggs may begin incubation with relatively cool temperatures that increase as incubation progresses. Given that the thermal sensitivity of embryonic growth and development tends to decrease over the course of incubation, exposure to cool temperatures at the start of incubation may have greater and more persistent effects on embryonic development and growth than exposure similar conditions later in incubation. We incubated Chelydra serpentina eggs under three different thermal conditions during the first 35 days of incubation (constant 25°C, increasing temperatures by 1°C weekly from 23 to 27°C, and decreasing temperatures by 1°C weekly from 27 to 23°C) then completing incubation for all three groups at a constant 25°C. We sampled embryos at Days 6, 12, 18, 24, 30, 36, and 50 to determine developmental stage and to obtain various size measurements (e.g., mass, head length). Embryos starting at 27°C were larger and more developed than those in the 25°C control group at Days 6, 12, and 18 (when temperatures were ≥ 25°C), but differences in developmental stage and size largely disappeared by Day 30. In contrast, embryos that began incubation at 23°C were smaller and less developed than those in the other two treatments at all sampling intervals and hatched later. These results indicate that low temperature exposure early in development creates a persistent lag in growth and development that cannot necessarily be compensated for with exposure to warmer temperatures later in incubation.


    4.  14:15  Castration and Testosterone Replacement Have Dose- and Tissue-Specific Effects in Garter Snakes. Rysa Thomas*, James Madison University; Shannon Richard, James Madison University; Julia Kaiser, James Madison University; M. Rockwell Parker, James Madison University   thoma6rl@dukes.jmu.edu

    Testosterone (T) has multifaceted effects on vertebrate organs, especially those associated with reproduction, and regulates partitioning of energy stores to affect body condition. Our study species, the red-sided garter snake (Thamnophis sirtalis parietalis), is a seasonally-reproducing reptile that experiences annual changes in circulating androgens and body composition. Androgens follow a general dissociated pattern in this species, peaking toward the end of the active season in late summer during gametogenesis, long after the intense mating season. In spring, males produce copulatory plugs to prevent subsequent female matings and deter competitors, and the kidneys are the principal source of this material while the testes are regressed. Because androgens, primarily T, are associated with sexual kidney function, we castrated (GX) males in the summer and replaced T in varying doses via silastic implants (T_low, T_med, T_high) in addition to a control group (SHAM; n=10 each). Snakes were bled every 3 months for implant validation, placed in artificial hibernation, then euthanized to collect kidney and other organ masses relative to body mass. Relative kidney mass was significantly decreased in GX but increased in all T groups compared to SHAM. Percent body fat was highest in GX compared to T_med and T_high, but rates of food intake and weight gain were invariable among the groups. Neither relative heart nor liver mass were altered by T treatments. Few tissues were responsive to T, and there may be a tradeoff between reproduction (e.g., sexual kidney hypertrophy) and energy storage (e.g., fat mass) influenced by androgens.


    5.  14:30  Testing the Immunocompetence Handicap Hypothesis: Environmental Androgens as a Model System for Steroid-Immune Interaction. Jorge Lopez-Perez*, Southeastern Louisiana University; Christopher Murray, Southeastern Louisiana University   jorge.lopez-perez@selu.edu

    Among environmental pollutants, endocrine disrupting compounds are some of the most threatening and enigmatic. The structural similarities of these molecules to endogenous hormones, such as estrogen or testosterone, facilitate their disruption of important endocrine pathways. It is well known that hormones influence many facets of physiology, however there is still contention regarding certain relationships; one such relationship being gonadal hormones and the immune system. In this study we tested the hypothesis that androgens inhibit immunocompetence using masculinized female American alligators (Alligator mississippiensis). Alligator eggs were incubated at female temperatures with a subset of individuals being exposed to 17-α-methyltestosterone prior to sexual determination at stage 20. Post-hatching, blood samples were collected for innate and acquired immune quantification assays. We found no significant differences between groups regarding heterophil: lymphocyte ratios or individual cell proportions. Additionally, we found no significant differences between treatment groups in assays quantifying innate immunity. However, we did find differences between groups in assays quantifying acquired immunity with MT individuals having a greater acquired antibody titer. Our data fail to support the hypothesis that androgens suppress immune function; however, 17-α-methyltestosterone may cause estrogenic effects within the immune system.


    6.  14:45  Tourism-Induced Effects on the Gut Microbiome of Bahamian Rock Iguanas. Erin Lewis, Utah State University; Karen Kapheim, Utah State University; Alison Webb, Utah State University; Charles Knapp, John G. Shedd Aquarium; John Iverson, Earlham College; Frank Oliaro, John G. Shedd Aquarium; Dale DeNardo, Arizona State University; Susannah French, Utah State University   e13.lewis@gmail.com

    Given an increase in ecotourism over the past several decades, human interaction with wildlife has become more prevalent and there is a high potential for both short-term and long term-effects on populations. Exploration of these potential impacts is necessary for developing effective conservation practices. The importance of gut microbial activity is also increasingly apparent, both in terms of individual and population-level health. Diet plays a key role in the development and maintenance of the microbiome with changes in consumption leading to changes in diversity and presence of certain bacterial species. Although many downstream effects are not entirely known or understood, dietary changes impacting the gut microbiome can have major impacts on physiological and immunological processes. Due to this link between diet and health through gut microbial composition, anthropogenic diet modifications are likely negatively impacting the physiological health of species in the wild. The practice of wildlife feeding is particularly prevalent and consistent in several populations of Bahamian Rock Iguana (Cyclura cychlura) in the Exumas, Bahamas, whereby several of the populations have been fed by tourists continuously over many years. We have been monitoring these populations for 40+ years and have recently focused on understanding dietary shifts in the microbiome. We found significant differences in microbiome composition and diversity between sexes and between populations with varying levels of tourist activity. These microbial changes and resulting physiological effects could lead to longer-term health issues and impact overall population health, as well as tourist activities and conservation practices.


    7.  15:00  Developmental Environment Has Lasting Effects on Amphibian Behavior and Thermal Physiology. Michel Ohmer*, University of Mississippi; Talisin Hammond, University of Pittsburgh; Samantha Switzer, University of Pittsburgh; Trina Wantman, University of Pittsburgh; Jeffery Bednark, University of Mississippi; Emilie Paciotta, University of Pittsburgh; Jordan Coscia, Virginia Tech; Corinne Richards-Zawacki, University of Pittsburgh   m.e.ohmer@gmail.com

    Environmental challenges early in development can result in complex phenotypic trade-offs and long-term effects on individual physiology, performance, and behavior, with implications for disease and predation risk. We examined the effects of simulated pond-drying and elevated water temperatures on development, thermal physiology, and behavior in a widespread North American amphibian, Rana sphenocephala. Tadpoles were raised in outdoor mesocosms under warming and drying regimes based on projected climatic conditions in 2070. We predicted that amphibians experiencing rapid pond drying and elevated pond temperatures associated with climate change would accelerate development and demonstrate long-term differences in physiology and exploratory behavior post-metamorphosis. Both drying and warming accelerated development and reduced survival to metamorphosis. At approximately one month post-metamorphosis, animals from the control (ambient no-drying) treatment jumped relatively farther at high temperatures in jumping trials. In addition, frogs with shorter larval periods had lower critical thermal minima and maxima. We also found evidence that developing under warming and drying resulted in a less exploratory behavioral phenotype, and that drying, but not warming, resulted in warmer thermal preferences. Furthermore, behavior predicted thermal preference, with less exploratory animals selecting higher temperatures. Our results underscore the multi-faceted effects of early developmental environments on behavioral and physiological phenotypes later in life. For example, thermal preferences can influence disease risk through behavioral thermoregulation, and exploratory behavior may increase risk of predation or pathogen encounter. By impacting thermal physiology, behavior, and various physiological traits, climatic stressors during development may mediate amphibian exposure and susceptibility to predators and pathogens into adulthood.


    8.  15:15  Hypoxia in ovo effects brain development and exploratory behavior in adult Leopard Geckos (Eublepharis macularius). Scott Parker*, Department of Biology, Coastal Carolina University; Ryan Yoder, Department of Psychology, Coastal Carolina University   slparker1968.sp@gmail.com

    Hypoxia can impair development of the embryonic central nervous system potentially causing behavioral deficits that persist into adulthood. The purpose of this study is to test the hypothesis that transient exposure to hypoxic conditions during embryonic development causes neural damage in brains of Leopard Geckos (Eublepharis macularius) resulting in impaired exploration performance in sexually mature individuals. We incubated late-stage Leopard Gecko eggs under hypoxia (9% O2) and tested kinematic properties of exploratory behavior in both hypoxia-treated and control geckos in an open-field arena at six to eight months after hatching. Movement patterns of individual geckos were recorded over 60 min in darkness using a digital camera. Total distance, peak speed, movement scaling (correlation between progression path length and peak speed), distance ratio, heading error, total stop time, mean stop time, number of stops, number of progressions, and progression distance were compared between hypoxia and control groups across five 10-minute intervals within trials. The hypoxia group had lower average peak speed (hypoxia: 5 cm s-1 vs control: 8 cm s-1) and increased movement scaling (hypoxia: mean r = 0.6) compared to controls (mean r = 0.37). No differences were found between groups for the other comparisons. Our results suggest that brain damage induced by in ovo hypoxia caused adult geckos to move more slowly than controls, and the hypoxia group’s strong correlation between progression distance and peak speed suggests they are able to accurately estimate distance. These preliminary results suggest in ovo hypoxia alters exploratory behavior that persists into adulthood.


    9.  15:30  Intraspecific variation of resting metabolism across elevation in Neotropical amphibians. Michael Britton*, Arizona State University; Maureen Donnelly, Florida International University   michaelryan.britton@gmail.com

    Metabolic effects of climate change are expected to be nearly universal among organisms exposed to changing temperatures. Metabolic impacts will be extensive in ectotherms, such as reptiles and amphibians, and will likely cause cascading effects on resource allocation, growth, reproductive output, and survival. Prediction and mitigation of metabolic impacts of climate change requires understanding of many aspects of metabolic ecology, including intraspecific variation. In this study, we examine the intraspecific variation in resting metabolic rate across elevation of three species of amphibians in the genus Pristimantis in southeastern Peru. Low variation and lack of correlation with environmental variables suggests that metabolic rate may be a relatively conserved trait in these taxa. Future work should examine individual repeatability, plasticity, and inheritability of metabolic traits to better understand the plastic and adaptive landscape that will influence potential metabolic responses of organisms to ongoing anthropogenic climate change.


    10.  15:45  Thermal factors influencing distribution of Panther chameleons (Furcifer pardalis) in Florida. Natalie Claunch*, University of Florida; Colin Goodman, University of Florida; Bryan Kluever, USDA, Wildlife Services, National Wildlife Research Center, Florida Field Station; Narayani Barve, Florida Museum of Natural History; Robert Guralnick, Florida Museum of Natural History; Christina Romagosa, University of Florida   nat.claunch@gmail.com

    The distribution and spread of non-native herpetofauna is primarily limited by cold temperatures, but acclimation or adaptation to cool temperatures may facilitate geographic expansion. Panther chameleons (Furcifer pardalis) have established populations in Florida, USA, in areas that may exceed cold temperatures in their native range in Madagascar. We evaluated the thermal performance, tolerance, and preference of panther chameleons and the acclimatization potential of these traits during exposure to naturally-occurring environmental conditions in North Central Florida at the USDA Wildlife Services National Wildlife Research Center, Florida Field Station. During fall, winter, and summer we examined locomotor performance at five body temperatures. We also measured critical thermal minimum, gaping threshold at high temperatures, and thermal preference in an arena with a thermal gradient. Spring trials were suspended due to treatment for an outbreak of dermatomycosis caused by Paranannizziopsis australasiensis. Though we observed temperature-dependent thermal performance, chameleons maintained similar critical thermal limits, performance, and thermal preferences across seasons, despite long-term exposure to cool temperatures and fungal infection in winter. While we did not find evidence of seasonal thermal acclimatization, we cannot rule out local adaptation in this population. An issue of management concern is that chameleon populations are often seeded in areas for future collection but kept secret due to their high value in trade. We apply our physiological data to mechanistic species distribution models and use an ensemble approach to predict potential locations of establishment for this cryptic species.




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