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    Reptile Morphology and Physiology

    2021-07-22   09:15 - 11:40

    Moderator: Patricia Brennan

    1.  09:15  IN-PERSON    Extraction of DNA from from reptile feces: What can we learn? Michael Westphal*, US Bureau of Land Management; Mark Statham, University of California at Davis; Deborah Woollett, Working Dogs for Conservation

    Extraction of DNA from indirect sources (eDNA) has become a burgeoning field in herpetology. By optimizing extraction of DNA from feces of the blunt nosed leopard lizard,Gambelia sila, we have provided a robust source of genomic data that has already proved valuable in multiple lines of research, including a groundbreaking study on the interactions of lizards with desert shrubs; evidence for decline ofG. silain an isolated preserve;and the discovery of a third species, the yellow-backed spiny lizard,Sceloporous uniformis, from multipe sites where it was not expected. Ongoing projects include characterization of reptile communities at two desert sites as well as population monitoring ofG. sila. We discuss the implications for research and conservation worldwide.

    2.  09:30  IN-PERSON    Across Valleys and Mountains: The Population Genetic Structure of the Herero Girdled Lizard (Namazonurus pustulatus). Jonathan DeBoer*, University of Nevada, Reno; Nathan Byer, University of Nevada, Reno; Jill Heaton, University of Nevada, Reno

    Girdled lizards are a diverse group of charismatic lizards that are often associated with rocky areas. Girdled lizard populations are declining due to habitat destruction and illegal wildlife trade, and as a result the group is CITES II protected. Additionally, there is limited knowledge on the natural history and biology of many species, but even more limited is population-level information. We investigated the genetic structure for a small-bodied, Namibian endemic cordylid, the Herero girdled lizard (Namazonurus pustulatus).Using single nucleotide polymorphism (SNP) data, we compared the genetic differentiation among nine localities throughout the known distribution (~120 x 100 km) of N. pustulatusto better understand their genetic structure and gene flow.Based on previous morphological analyses that demonstrated body and head size differences between low (1200–1700 m) and high (1900–2300 m) elevation localities, we predict that we will observe population genetic differentiation between elevational classes as well, but also see a relationship of greater increased genetic differentiation with distance. Genetic clustering analyses indicate genetic structuring in N. pustulatus. Pairwise Fstindicate genetic differentiation associated with elevation, where genetic diversity within elevation class is more similar than among elevation class. In addition, differing levels of gene flow indicate connectivity among some localities, but not others. Further work on the Herero girdled lizard will focus on potential patterns of local adaptation, as shaped by the environment, associated with differing elevational gradients.

    3.  09:45  IN-PERSON    3D Imaging of the Lizard Adhesive System via Photogrammetry. Travis Hagey*, Mississippi University for Women; Rishab Pillai, James Cook University; Jendrian Riedel, James Cook University; Lin Schwarzkopf, James Cook University

    The adhesive toes of geckos and other lizards are an amazing example of naturally occurring nanotech. A basic step in understanding the structure, function, and variation in the micro and nano-scale structures of gecko toes is the ability to visualize and image these very small yet complex structures easily and accurately. This can be a difficult endeavor. Electron microscopy is a common high-resolution imaging approach, with magnifications capabilities over 50,000X, yet electron microscopy can suffer from optical distortions and is typically limited to 2D images. In order to produce accurate 3D models of micro and nano-scale structures, we have developed an approach to combine electron microscopy with a 3D photogrammetry, which uses a collection of 2D images to produce a 3D reconstruction. Data collection for photogrammetry is straight forward and inexpensive. To investigate the use of photogrammetry to digitally reconstruct scanning electron microscopy images, we imaged and reconstructed micron-scale adhesive structures from three gecko species (Gekko gecko, Correlophus ciliates, and Oedura coggeri). In these species, the adhesive structures range from 100um tall in G. gecko to 30um tall in C. ciliates, with O. coggeri having intermediate sized structures. We will explain how to prepare samples, collect images, and conduct 3D reconstructions. Geckos (and other pad bearing lizards) use a wide variety of surfaces in the wild. Gaining a better understanding of their adhesive morphology is an exciting first step to better understanding how species are adapted to specific scansorial microhabitats.

    4.  10:00  IN-PERSON    Genital coevolution: 3-D morphology and geometric morphometrics of male and female genitalia in watersnakes (Nerodia sp). Patricia Brennan*, Mount Holyoke College; Genesis Lara Granados, Mount Holyoke College; Juliet Greenwood, Mount Holyoke College; Brandon Hedrick, Lousiana State University; Stephen Secor, University of Alabama; Brian Todd, University of California Davis

    Snakes have diverse hemipene morphology, but we know little about why this diversity evolved. One limitation to understanding the evolution of diverse hemipenes, is that female genital morphology is little studied. Genitalia, more than any other trait, have to mechanically interact between males and females, so they are expected to coevolve. Understanding this coevolution can help us discriminate possible mechanisms of evolutionary divergence. Here we present data from two projects relating to the study of genital morphology in snakes of the Genus Nerodia using 2-D and 3-D geometric morphometrics to explore patterns of intra and interspecific variation in the shape of the hemipene and the vaginal pouch, and their association with SVL and reproductive status. In N. rhombipher, we found that as males and females get larger, their genitalia become wider and more bilobed, suggesting close coevolution. We also found an isometric relationship between SVL and centroid size in both males and females. A three-way comparison between N. rhombipher, N. sipedon and N. fasciata, suggests that the bilobed hemipene shape is associated with a reduction of the basal spines, and a corresponding widening of the cloacal opening in females, and the development of deep bifurcation of the vaginal pouches. Morphological disparity measurements suggest that changes in female genitalia preceded changes in male genitalia. This work is the first to examine genital variation in males and females in 3-D, and is part of a large ongoing comparative study that seeks to understand patterns of genital evolution in snakes.

    5.  10:45  IN-PERSON    Physiological thermoregulation in lizards and implications for distribution using a mechanistic modeling approach. Caleb Loughran*, University of New Mexico; Blair Wolf, University of New Mexico

    In lizards, there is considerable variation in the ability to dissipate heat loads through evaporative cooling via panting, which effects how long lizards can spend exposed to high solar heat loads. While the differing capacities of lizards to depress body temperature (Tb) through evaporative cooling via panting have been described, here we present data that link panting and Tb depression with rates of evaporative water loss. In this study, we used flow-through respirometry to measure evaporative water loss rates and metabolism of 5 species of Sceloporusfrom the American southwest while simultaneously measuring Tb. We exposed lizards to air temperatures (Ta) ranging from 35°C to their critical thermal maximum. We found that evaporative cooling costs substantially varied among species, with metabolic panting effort significantly affecting lizards’ evaporative capacity. Across species, there was a significant positive relationship between the overall rate of evaporative heat loss and maximum Ta-Tb gradient a species could maintain. We applied this data to the mechanistic niche model NicheMapR to estimate how panting may augment lizard activity in different habitats across a species’ range. For each species, we used three geographic locations that ranged from the lowest to highest recorded elevations to construct a microclimate model that a lizard may experience. Across species, we found that panting significantly extends activity periods for lizards in higher elevation habitats, but minimally augments activity hours in lower, hotter habitats. We discuss the adaptive significance of thermoregulatory panting, and how it may give some species a competitive edge as climates warm.

    6.  11:00  IN-PERSON    Innate Immune Function in Lake Erie watersnakes (Nerodia sipedon insularum) with Ophidiomycosis. Ellen Haynes, University of Illinois; Sarah Baker*, McNeese State University; Mark Merchant, McNeese State University; Kristin Stanford, Franz Theodore Stone Laboratory, The Ohio State University; Matthew Allender, University of Illinois

    Ophidiomycosis, caused by the fungus Ophidiomyces ophidiicola, poses a threat to the health of wild and managed snakes worldwide. Variation in snake innate immunity, the primary defense against infection in reptiles, may explain the observed variation in ophidiomycosis clinical disease severity among snakes. Two components of the innate immune response were examined using snake plasma: the complement cascade and chitotriosidase, a chitinase that is involved in the response to fungal pathogens. Specifically, we investigated whether complement activity, as measured by sheep red blood cell lysis, and chitotriosidase activity were associated with ophidiomycosis disease severity and time in captivity in Lake Erie watersnakes (Nerodia sipedon insularum). Generalized linear regression modeling found no difference in hemolysis or chitotriosidase activities among snakes with no lesions or mild, moderate, or severe ophidiomycosis. Based on mixed effects logistic regression modeling, hemolysis activity increased with time in captivity, while chitotriosidase activity did not change over time. However, among snakes with lesions kept in captivity, chitotriosidase activity was significantly higher in snakes with mild disease, compared to snakes with severe disease. Overall, Lake Erie watersnakes had higher complement activity, but lower chitotriosidase activity, compared to other reptile species, and this is the first description of chitotriosidase activity in a snake species. These results suggest that innate immune function may be associated with ophidiomycosis severity, but more work is needed to investigate differences among snake species.

    7.  11:15  IN-PERSON    It’s All In The Head: Understanding How Constriction Works In Snakes. David Penning*, Missouri Southern State University; Jillian Hackney, Missouri Southern State University

    Many snakes employ venom or constriction to subjugate and/or kill their prey. The mechanisms of constriction involve snakes wrapping or winding their body around prey while contracting muscles to produce high pressures. Our current understanding of how pressure impacts the tissues of prey is growing but remains incomplete. Currently, there are several hypotheses about how these high pressures impact prey that are being constricted. The hypotheses include suffocation, cardiac trauma and arrest, blunt force trauma, and neural damage. The red-out effect is the most recently proposed hypothesis that aims to explain how constriction works. It posits that when snakes constrict their prey, they are able to drive blood and bodily fluids towards the head of their prey, quickly incapacitating them. This eventually leads to the shutdown of the nervous system. However, this hypothesis was generated from multiple indirect inferences about constriction. Here, using boas (Boa constrictor [n=5], Lichanura trivirgata [n=2], and Corallus hortulanus [n=3]) and pythons (Python breitensteini [n=7], Morelia spilota [n=10], and Morelia viridis [n=3]), we quantified constriction pressures within both the chest and cranium of prey to provide evidence for the newly proposed red-out effect. Both thoracic and intracranial pressures within prey significantly increased with increasing snake mass. However, maximum thoracic pressures were not correlated with maximum intracranial pressures in prey. Regardless of the thoracic pressure delivered, all prey experienced similarly high intracranial pressures. Not only were thoracic pressures high enough to induce cardiac arrest, intracranial pressures were surprisingly high within the skulls of rodent prey.

    8.  11:30  VIRTUAL    Does Access to Hindgut Microbial Symbionts affect the Growth Rate of a Herbivorous Reptile? Andrew P. St. Julian*, California State University, Northridge; Gilberto E. Flores, California State University, Northridge; Christopher R. Tracy, University of California, Riverside; Robert E. Espinoza, California State University, Northridge

    Microbial symbioses are ubiquitous in animals and researchers are only beginning to understand the diverse roles these communities play in host performance. For example, herbivorous vertebrates lack endogenous cellulases and must therefore rely on symbioses with microbes (e.g., archaea, bacteria, protists, and fungi) that reside in their guts to decompose the fibrous components (e.g., cellulose) of their plant diets. In herbivorous reptiles, the products of microbial fermentation can account for >30% of the host’s energy budget. Because herbivorous reptiles are born with sterile guts, they must acquire these essential microbes soon after hatching or birth, yet when and where these microorganisms originate has scarcely been investigated. Researchers have suggested that a likely source of these microbes is the feces of older individuals, which are eaten by neonates. We tested this hypothesis on hatchling Chuckwallas (Sauromalus ater) by comparing growth rates of neonates that had adult feces mixed in their lab diets (treatment) to a group fed the same diet without feces (control). After ~180 d on the diets, we found hatchlings in the control group had faster rates of growth than those in the treatment group—contrary to our predictions. Next we will characterize temporal changes in these microbial communities using 16S rRNA gene amplicon sequencing so we can assess how the diet treatment altered microbial community dynamics over the 6-mo growth period, and potentially explain these paradoxical results. Our study is the first to experimentally test how exposure to microbial symbionts alters growth in a developing herbivorous reptile.

    9.  11:35  VIRTUAL    Tissue, Seasonal, and Sex-Specific Steriodogenic Gene Expression in Garter Snakes. Julianna M. Lincoln*, James Madison University; Megan L. Barlowe, James Madison University; M. Rockwell Parker, James Madison University

    Sex steroid hormones are vitally important in vertebrate reproduction because they regulate gametogenesis and sex behavior in seasonally breeding species. Seasonal steroid hormone patterns occur in sequence or synchrony with major reproductive events. But, how and to what degree various tissues contribute to sex steroid production are important questions in comparative physiology. The red-sided garter snake (Thamnophis sirtalis parietalis) has a strongly seasonal reproductive pattern where sex steroids dictate multiple facets of the snake’s natural history. The purpose of our study is to determine whether mRNA expression of key steroidogenic enzymes (StAR, Cyp17?1, 17?HSD3, and Cyp19?1 [aromatase]) vary seasonally within the gonads and liver of female and male red-sided garter snakes. We will be extracting mRNA from tissues collected during spring, summer, and fall in both sexes and performing qPCR to assess gene expression. In female liver and ovaries, we predict aromatase and StAR expression to peak in summer, coincident with gametogenesis; Cyp17?1 and 17?HSD3 will have an opposite pattern as seen in other reptiles. However, since male gametogenesis lags behind female gametogenesis, StAR, Cyp17?1, and 17?HSD3 should peak in fall. We predict testis and liver aromatase to remain at low levels throughout the year because these are not the main sites of aromatization compared to the brain and ovary in males and females, respectively. The seasonal modulation of these steroidogenic enzymes should align with known patterns of gametogenesis observed in this population.

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