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    P2: Herpetology: Morphology & Histology

    2021-07-27   16:00 - 18:00

    To view the posters go to You will be able to chat one-on-one during the Tuesday poster session, the e-poster platform.

    1.  16:00  A morphometric analysis of Ambystoma vertebrae and implications for the identification of fossil salamanders. David Ledesma*, The University of Texas at Austin; Melissa Kemp, The University of Texas at Austin

    Ambystomarepresents a speciose clade of salamanders that are found across much of North America. FossilAmbystomaare known from early Cenozoic deposits and are fairly common in Quaternary fossil deposits. Most fossils identified asAmbystomaare isolated vertebrae. Both quantitative and qualitative features have been purported as being useful for identifying fossilized vertebrae ofAmbystomato the species-level. However, there is limited information on intraspecific variation in these features and previous studies noted intracolumnar variation which affects the utility of those features for fossil identification. A lack of understanding of variation in modern species ofAmbystomacasts uncertainty on our ability to confidently identify fossil vertebrae to the species level. Our aim was to document intraspecific and intracolumnar variation in vertebral morphology among species ofAmbystomaand examine the implications for fossil identification. We took linear measurements on 15 species ofAmbystomaand assessed the degree to which we can use linear morphometrics for differentiating species. We also conducted 2D geometric morphometric analyses on the atlas of 15 species ofAmbystoma. We apply these morphometric data in a case study where we attempt to identify fossil vertebrae from a Quaternary fossil locality in central Texas. We found that our morphometric data are of little use for differentiating species ofAmbystoma. However, above the species level, morphometric data may be useful for differentiating between some clades withinAmbystoma. Using our dataset, we identified fossil vertebrae from our case study as likely belonging to a clade withinAmbystoma.

    2.  16:00  Fluorescence Helps Illuminate Anatomy in Tadpoles. Bailey Richards*, St. Cloud State University; Jennifer Lamb, St. Cloud State University

    Accurate species identification is essential for assessing biodiversity. One method of differentiating among larval anurans (frogs and toads) is by examining their oral disc (mouthparts). Portions of the oral disc are semi-transparent and difficult to see. This issue can be addressed by using different stains, but this may not be an option when working with museum specimens. Fluorescence has recently been identified as a way to study anatomy in preserved specimens and fossils, but to our knowledge it has not been used to examine tadpoles. We tested different combinations of stains and lighting conditions to determine how to improve visualization of the oral disc. We examined fresh-dead and recently preserved larval Wood Frogs (Lithobates sylvaticus) and larvae in the Grey Tree Frog Complex (Hyla chrysoscelis, H. versicolor). We also examined museum specimens caught in the 1950s and 2000s. We illuminated oral discs with white, blue (440-460 nm), and ultra-violet light (360-380 nm), and photographed specimens prior to and after staining with different dilutions of crystal violet or methylene blue. Keratinized mouthparts were most easily seen via fluorescence in response to blue light, or when stained with methylene blue and viewed under white light. When viewing the non-keratinized parts of the oral disc, the soft anatomy was easily seen with a methylene blue stain, but the details of the papillae and labia were also apparent via fluorescence. These results confirm that while stains do help when examining tadpole oral disc morphology, there are other effective options, including fluorescence.

    3.  16:00  Intrasexual selection drives differences in male skull morphology of closely related species within the Limnonectes kuhliicomplex (Anura: Dicroglossidae). Thornton Larson*, University of Texas at Arlington; Justin Jacobs, University of Texas at Arlington; Amir Hamidy, Museum Zoologicum Bogoriense, Indonesian Institute of Science; Nia Kurniawan, Brawijaya University; Eric Smith, University of Texas at Arlington

    In the fanged-frog genus Limnonectes, males are larger than females at maturity with the size discrepancy attributed to their large heads. Big headedness is often attributed to sexual selection arising from male-male fighting for appropriate egg laying habitat. Larger frogs usual win and the habitat attracts more females to it. Sexual dimorphism driven by sexual selection in amphibians has contributed to the hyper diversity of frogs found in tropical regions. Previous morpho-descriptions are focused on species level descriptions, demonstrating that skull morphology can differentiate between Limnonectes species, further attributed to differences in mating behavior of species in the genus. However, no osteological description currently exists between male and female individuals within a species. I present high-resolution computed microtomography (CT) scans of skulls from males and females of the species Limnonectes kuhlii from Sumatra, where three-dimensional geometric morphometric analyses were used to quantify the variation between males and females using fixed landmarks. Standard measurements were taken to expand the sample size. The goal of this study is to identify differences in the skull morphology between males in Sumatran Limnonectes kuhlii. Females demonstrate less restriction in body size features than males, making mensural markers difficult to use for identification purposes. These findings quantify a suite of sexually dimorphic traits in skull morphology which likely arise from behavior such as male-male combat. Specific trends in skull sexual dimorphism may be species specific and highlight further environmental drivers of speciation within the genus.

    4.  16:00  Gecko Foot Musculature: Using DiceCT Scans in Ecomorphological Analyses. Yuanxing Liao*, Villanova University; Aaron Bauer, Villanova University

    The diverse habitats inhabited by geckos make them perfect candidates for ecomorphological analyses. Previous ecomorphological studies on the gecko locomotor apparatus largely focused on external morphology and osteology but ignored the muscular system. The locomotor apparatus works as an integrated whole and the muscles play a critical role in generating forces, facilitating adhesion and positioning the limbs while moving. In addition, previous muscle descriptions relied on gross dissection and were largely limited by the size of the animal and likely missed some fine details. In this study, I used high resolution Diffusible Iodine-based Contrast-enhanced Computed Tomography (DiceCT) to reexamine the foot musculature of Gekko gecko, a model gecko species for comparative anatomy and functional morphology. I also measured the volume of muscles which are critical for adhesion and locomotion in 9 additional species in different gekkotan families to examine variation across phylogeny and habitat type. Overall, the origination and insertion of the Gekkofoot muscles described by previous dissection are largely congruent with what is revealed by high resolution CTs but there are some differences, especially at finer scales. Phylogeny plays a significant role in muscle morphology, whereas habitat explains a lesser portion of the variation. This study points to the value of CT scanning in discerning and describing fine soft anatomical structures in the autopodium and to the integration of both phylogeny and habitat in shaping the morphology of the locomotor apparatus.

    5.  16:00  Comparative Skull Morphology of Mainland African Plated Lizards (Squamata; Gerrhosauridae). Kelsey Fenner*, Villanova University

    Gerrhosaurs are heavily armored lizards encased by adherent osteoderms. Historically, this has made it difficult to study their cranial morphology. Among the five genera inhabiting mainland Africa, there is a largely bimodal size distribution. Three exhibit large body size (up to 300 mm SVL) and two small body size (up to 80 mm SVL), with few species exhibiting an intermediate size. I hypothesize that this split in body size is due to miniaturization in the two smaller genera, Tetradactylus and Cordylosaurusin relation to the three larger genera Broadleysaurus, Matobosaurusand Gerrhosauruswhich exhibit a body size more consistent with their closest relatives, Madagascan gerrhosaurs and cordylids.Using micro-computed tomography, I digitally removed many of the osteoderms to reveal the underlying structures. This allowed for in depth analysis of both the skull as a whole and each individual skull bone across all five genera. Previous studies on the skull morphology of gerrhosaurs have mainly focused on features of the intact skull, and none of the nine species I studied have been been digitally segmented using CT-scanning technology. All nine species studied exhibited many skull bones that are cancellous in comparison to those of other lizards. The two smaller genera show more fusion in their lower jaw bones, a more posteriorly projecting basicranium, both of which have been associated with miniaturization in other squamates.

    6.  16:00  Morphological Variation of Cranial Elements in the Western Massasauga. John Jacisin, Department of Ecology and Conservation Biology, Texas A&M University; Corey Fielder, Natural Resources Institute, Texas A&M University; Danielle Walkup*, Natural Resources Institute, Texas A&M University; Toby Hibbitts, Biodiversity Research and Teaching Collections, Department of Ecology and Conservation Biology, Natural Resources Institute, Texas A&M University; Wade Ryberg, Natural Resources Institute, Texas A&M University; Jesse Meik, Department of Biological Sciences, Tarleton State University; A. Michelle Lawing, Department of Ecology and Conservation Biology, Texas A&M University

    Understanding the correspondence between ecological and morphological variation across populations provides insight into both taxonomic distinctions and the functionality and performance of traits in different environments.To examine morphological variation of cranial and soft tissue elements across the geographic distribution of Western Massasauga (Sistrurus tergeminus) populations, and to examine the differences between its two subspecies, we performed microcomputed tomography (micro-CT) scans of 129 museum. We developed landmark schemes of dorsal and left lateral skull orientations, then used Procrustes superimposed landmarks to translate, rotate, and scale the schemes. We ordinated the landmarks with a principal component analysis and used linear discriminant functions to test the reliability of taxonomic assignments. We also scored eight aspects of squamation for all individuals and made 15 additional soft-tissue morphology measurements. Preliminary analyses of the skull in the dorsal view showed that PC1 (42.9% explained variance) represents an axis of nasal and premaxilla elongation and braincase, orbital, and occipital region compression, potentially associated with among-population dietary differences. In the skull lateral view, PC1 (21.4% explained variance) represents the relative height of the skull as well as the relative length of the quadrate. These changes directly affect both the possible angles and the proportions of the lever system in the jaw and should therefore have a direct effect on the prey sizes available to an individual. Preliminary results for soft-tissue morphology show most variables differ between individuals based on the different subspecies designations, wherediscriminant functions identified subspecies with 85.2% and 91.2% accuracy, respectively.

    7.  16:00  Morphology of Terrapene carolina in Coastal Mississippi. Evan Grimes*, University of Southern Mississippi; Brittany Maldonado, Southeastern Louisiana University

    Recent insights into the genetics and evolutionary history of North American box turtles have raised important questions regarding cryptic evolutionarily significant units within the genusTerrapene. This is especially true regarding the Eastern Box Turtle (Terrapene carolina) in the southeastern extent of its range. Introgression analyses suggest distinct lineages along the Gulf Coast. Morphological analyses in this understudied region may highlight differences in size, carapace patterning, and sexual dimorphism. We surveyed suburban populations of box turtles in coastal Mississippi from March 2020 to October 2020. We recorded morphometric (e.g. carapace length, carapace width) and qualitative (e.g. eye color) characters. We estimated age from annuli when possible and sexed adults. We marked each turtle with a unique numerical code. In 2020, we captured, measured, and marked 120 individuals. Of the 102 adults captured, 53 were female and 49 were male. Mean carapace length was 163.46 mm, mean carapace width was 126.59 mm, and mean weight was 805.57 g. While females and males had similar shell heights, we observed differences in weight, carapace length, and carapace width. Surveys are currently ongoing for 2021.

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