Symposium: The Biology of Whiptail Lizards IRoom: Room 206C2022-07-31 10:00 - 12:00 |
| Moderator: Anthony Barley |
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1. 10:00 Chromosome Acrobatics in Parthenogenetic Whiptail Lizards. Peter Baumann*, Johannes Gutenberg University pebauman@uni-mainz.de
Historic hybridization events between different species of whiptail lizards (genus Aspidoscelis) gave rise to rare hybrids with the ability to reproduce clonally by true parthenogenesis. Such clones have colonized large parts of the American Southwest and subsequent hybridization events gave rise to triploid and even tetraploid species. Using cytological analysis, we have begun to shed light on how the program of oogenesis is modified to permit fundamentally different modes of reproduction in closely related species. In parthenogenetic females, oocytes contain four instead of two sets of chromosomes during the diplotene stage and the pairing and recombination that normally occurs between homologous chromosomes is replaced by the pairing of identical chromosomes. The two meiotic divisions then generate a diploid instead of haploid egg that does not require fertilization to restore the somatic chromosome number. We will discuss an unexpected mechanism by which the chromosome number is doubled during meiotic prophase to permit parthenogenetic oogenesis. |
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2. 10:15 The evolutionary network of whiptail lizards (Aspidoscelis) reveals predictable outcomes of hybridization. Anthony Barley, University of California; Adrián Nieto-Montes de Oca, Universidad Nacional Autónoma de México; Norma Manríquez-Morán, Universidad Autónoma del Estado de Hidalgo; Robert Thomson*, University of Hawai?i thomsonr@hawaii.edu
Hybridization between diverging lineages has diverse outcomes that range from the generation or loss of species diversity, introgression and adaptation (whether associated with speciation or not), as well as changes in reproductive mode and ploidy. The factors that mediate when and why these divergent outcomes occur are poorly understood. We estimate a comprehensive evolutionary network for the North American whiptail lizards (Aspidoscelis) and use it to understand the evolutionary outcomes of hybridization. Our results show that rates of introgression between species decrease with time since divergence and suggest that species must attain a threshold of evolutionary divergence before hybridization results in transitions from sexual to unisexual reproduction. Rates of hybridization also predict genome-wide patterns of genetic diversity in whiptail lizards. These results distinguish among models for the outcomes of hybridization that have not previously been tested and suggest that these outcomes are predictable in the largest group of unisexual vertebrates. |
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3. 10:30 Allele Specific Expression in Asexual Whiptail Lizards (Aspidoscelis neomexicanus). Valentine Patterson*, Johannes Gutenberg University; David Ho, Johannes Gutenberg University; Nathaniel Deimler, Johannes Gutenberg University; Peter Baumann, Johannes Gutenberg University vapatter@uni-mainz.de
Whiptail lizards of the genus Aspidoscelis consist of bisexual and unisexual species. Sympatry, as well as the overlapping territories of the species within this genus has facilitated multiple hybridization events between these bisexual species, giving rise to new hybrid unisexual species. One such instance of a hybridization event is between two diploid bisexual species, A. marmoratus and A. inornatus, resulting in a diploid hybrid unisexual offspring – A. neomexicanus. Due to the maintenance of these two parental genomes through obligate parthenogenesis, this hybrid species has a high level of heterozygosity. This is often thought as the reason why they are evolutionary successful, despite the lack of genetic diversity generated through sexual reproduction. Therefore, we use the hybrid A. neomexicanus as a key study organism to investigate a wide range of questions, including the genetic and epigenetic diversity present in the lizards. Moreover, this gives us a unique model system to study allele-specific expression, the preferential expression of one allele versus the other. Understanding these allele-specific expression differences can help elucidate the maintained fitness and success of A. neomexicanus and other unisexual species. |
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4. 10:45 Genomics of Aspidoscelis Whiptail Lizards. David Ho*, Johannes Gutenberg University; Valentine Patterson, Johannes Gutenberg University; Nathaniel Deimler, Johannes Gutenberg University; Peter Baumann, Johannes Gutenberg University dho@uni-mainz.de
Parthenogenetic whiptail lizards of the genus Aspidoscelis arose by interspecific hybridization between two different species from within this genus. These hybrid unisexual, all-female species are viable and reproduce clonally through obligate parthenogenesis. In addition, these unisexual species also vary in ploidy levels and have genomes that consist of various combinations of ancestral, bisexual species. In order to develop genomic resources for these unisexual species, we sequenced and assembled the genomes of three bisexual species, whose genomes are commonly found in the unisexual species:A. gularis, A. inornatus, and A. marmoratus. The A. gularis assembly, although still at scaffold-level, is highly contiguous. The chromosomal-level assemblies of A. inornatus and A. marmoratus confirm a high degree of synteny between the species and shed light on several chromosomal rearrangements that distinguish the karyotypes. Additionally, using transcriptomic data, we have also identified 29,351 and 29,572 protein-coding genes for these two respective genomes. A. neomexicanus is a diploid, unisexual that resulted from the single hybridization between A. inornatus and A. marmoratus. We have shown that combining the two bisexual reference genomes together as a proxy for A. neomexicanus has shed light on the biology of the species. These reference genomes serve as a valuable resource to the study not only the bisexual and unisexual Aspidoscelis species but of squamate evolution as well. |
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5. 11:00 Lower Mitochondrial Respiration in Hybrid Parthenogenetic Lizards (genus Aspidoscelis). Randy Klabacka*, Auburn University and Museum of Natural History; Hailey Parry, NHLBI NIH; Kang Nian Yap, Norwegian University of Science and Technology; Ryan Cook, Villanova University; Victoria Herron, University of Missouri; L. Miles Horne, University of Texas at El Paso; Matthew Wolak, Auburn University; Jose Maldonado, University of Texas at Arlington; Matthew Fujita, University of Texas at Arlington; Andreas Kavazis, Auburn University; Jamie Oaks, Auburn University and Museum of Natural History; Tonia Schwartz, Auburn University klabacka.randy@gmail.com
The infrequency of asexual reproduction across vertebrates as a whole suggests a fitness cost. Here we quantify organismal (endurance capacity) and intracellular (mitochondrial respiration) performance traits in two parthenogenetic species within the genus Aspidoscelis (A. neomexicanus and A. tesselatus). Because vertebrates that reproduce asexually are of hybrid origin, we compared these measurements to their parental sexual species (A. inornatus, A. marmoratus, and A. septemvittatus). We found reduced endurance capacity and mitochondrial respiration in the hybrid parthenogenetic species compared to the parental sexual species. Additionally, the variation in some traits is lower in the hybrid parthenogenetic species compared to the parental sexual species. We compare these findings to those of previous studies, and discuss potential hypotheses within the context of mitonuclear and evolutionary ecology. |
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6. 11:15 Stable isotope ecology of unisexual and sexual Aspidosceliswhiptail lizards. Maggie Grundler*, UC Berkeley; Doug Burkett, ECO-Inc.; Erica Bree Rosenblum, UC Berkeley mgrundler@berkeley.edu
The astounding diversity of Aspidoscelis whiptail lizards, manifesting in mosaic communities of unisexual and sexual lineages, presents a unique opportunity to isolate the effects of environmental and genetic variation on ecological phenotypes. Dietary preference in particular is one of the most important components of an organism’s life history, yet this trait has received little attention in studies of molecular evolution. To better understand the contribution of genetic diversity and phenotypic plasticity to dietary ecology, we analyze niche variation in populations of sexual and unisexual whiptail lizard communities at two seasonal timepoints. Using stable isotope ratios from tissues with different metabolic turnover rates, we quantify individual, interindividual, and population niche widths in mixed whiptail communities dominated by either a sexual or unisexual lineage. With these metrics, we compare the dietary lability of sexual and clonal lineages to assess the extent to which genetic diversity facilitates dietary shifts in response to competition and environmental changes. |
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7. 11:30 Microbial Diversity of Sexual and Parthenogenetic Whiptail Lizards (Aspidoscelis). Kathleen Currie*, The University of Texas at Arlington; Matthew Fujita, The University of Texas at Arlington kathleen.currie@uta.edu
Animals harbor numerous communities of microorganisms throughout their bodies, which are collectively referred to as the microbiome. The communities of each body site contribute in different ways to the overall physiology and health of the host, though the gut microbiome is of particular interest to researchers due to its complex relationship with the host’s immune system and development. While the number of studies investigating these relationships in non-model vertebrate systems is increasing, squamates remain poorly represented despite their potential as great models for microbiome research. We sampled populations of both sexual and asexually reproducing species of whiptail lizards (genus Aspidoscelis) from locations across four different biomes in the southwestern United States in order to investigate how gut microbiomes vary between divergent lizard reproductive modes. Utilizing high-throughput sequencing of the 16S rRNA gene, we were able to characterize and compare the cloacal microbiome communities and found that the top three bacterial phyla across all biomes were Actinobacteria, Firmicutes, and Proteobacteria. Specifically within the Warm North American Deserts biome, we found the Shannon diversity index of the sexual populations to be significantly higher than that of asexual populations. Furthermore, we observed that microbial diversity varies across biomes. By leveraging parthenogenetic and sexual whiptails, our results highlight that microbiome diversity is affected by both host biology and environment. |
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8. 11:45 Physiology, Distribution, and Reproductive Investment in the Colorado Checkered Whiptail (Aspidoscelis neotesselatus) in an Anthropogenically Disturbed Site. Megen Kepas*, Utah State University; Lise M. Aubry, Colorado State University; Spencer B. Hudson, Utah State University; Layne Sermersheim, Utah State University; Anna-Joy Lehmicke, Fort Carson Military Base; Douglas Eifler, The Erell Institute; Bryan M. Kluever, USDA; Susannah S. French, Utah State University megenkepas@gmail.com
The Colorado Checkered Whiptail (Aspidoscelis neotesselatus) is a parthenogenetic species of whiptail lizard that is listed as a “species of special concern” in the state of Colorado. This species occupies a small geographic range which extends onto the Fort Carson Military Base in Colorado Springs, Colorado. We sampled 82 females during the reproductive season to assess whether capture location, scheduled anthropogenic disturbances, and reproductive status correlated with measures of free and stored energy. We measured the blood levels of the hormone corticosterone as a marker of induced stress, glucose and cholesterol as measures of free energy, and triglycerides and tail circumference as measures of stored energy. Clutch size and stage were determined by abdominal ultrasound. Location and physiological data for recaptured individuals during the 2021 season were compared with an individual’s previous data (2018 and 2019) to assess individual range sizes, clutch sizes, and body condition across multiple seasons. |