Mitochondrial genetic variation within and between Holbrookia lacerata lacerata and Holbrookia lacerata subcaudalis, the spot-tailed earless lizards of Texas

METASTATIC MINERALIZATION IN A ZOOLOGIC COLLECTION OF SPOT-TAILED EARLESS LIZARDS (HOLBROOKIASPP.)

Vitamin and mineral supplements are commonly used in diets for zoologic and companion animals. Because specific nutrient requirements are often unknown, informed decisions are based on literature for related species. Over 18 mon beginning in November 2017, an entire population of spot-tailed earless lizards (Holbrookia lacerata and Holbrookia subcaudalis) died (N = 33). All but two lizards were submitted for histopathology (94%). All examined cases had mineralization in at least one tissue; 71% (22 of 31) had multisystemic mineral deposits consistent with metastatic mineralization. No underlying causes were detected histologically. The supplement used for dusting the food items fed five to six times per week was inadvertently switched for 2 to 4 mon, and the incorrect supplement was found to contain fourfold the intended vitamin D3 concentration. Thus, hypervitaminosis D was considered the most likely cause. Interestingly, eastern collared lizards (Crotaphytus collaris), also fed prey supplemented five to six times a week, and over 50 other insectivorous reptile and amphibian species possibly receiving the supplement one to seven times a week did not appear affected. During this time, only two other cases of metastatic mineralization were diagnosed in other herpetofauna at this institution. Prior to receiving the incorrect supplement, there were no cases of metastatic mineralization detected in the earless lizard population. These cases highlight species-specific sensitivities, and the deleterious effects of excessive or inappropriate supplementation. It is important to confirm product identification on arrival, regularly conduct chemical analysis of supplements, and educate keepers and owners about adverse effects of inappropriate supplementation.

Parthenogenesis doubles the rate of amino acid substitution in whiptail mitochondria

Sexual reproduction is ubiquitous in the natural world, suggesting that sex must have extensive benefits to overcome the cost of males compared to asexual reproduction. One hypothesized advantage of sex with strong theoretical support is that sex plays a role in removing deleterious mutations from the genome. Theory predicts that transitions to asexuality should lead to the suppression of recombination and segregation and, in turn, weakened natural selection, allowing for the accumulation of slightly deleterious mutations. We tested this prediction by estimating the dN/dS ratios in asexual vertebrate lineages in the genus Aspidoscelis using whole mitochondrial genomes from seven asexual and five sexual species. We found higher dN/dS ratios in asexual Aspidoscelis species, indicating that asexual whiptails accumulate nonsynonymous substitutions due to weaker purifying selection. Additionally, we estimated nucleotide diversity and found that asexuals harbor significantly less diversity. Thus, despite their recent origins, slightly deleterious mutations accumulated rapidly enough in asexual lineages to be detected. We provide empirical evidence to corroborate the connection between asexuality and increased amino acid substitutions in asexual vertebrate lineages.

Transcriptome sequencing reveals signatures of positive selection in the Spot-Tailed Earless Lizard

The continual loss of threatened biodiversity is occurring at an accelerated pace. High-throughput sequencing technologies are now providing opportunities to address this issue by aiding in the generation of molecular data for many understudied species of high conservation interest. Our overall goal of this study was to begin building the genomic resources to continue investigations and conservation of the Spot-Tailed Earless lizard. Here we leverage the power of high-throughput sequencing to generate the liver transcriptome for the Northern Spot-Tailed Earless Lizard (Holbrookia lacerata) and Southern Spot-Tailed Earless Lizard (Holbrookia subcaudalis), which have declined in abundance in the past decades, and their sister species, the Common Lesser Earless Lizard (Holbrookia maculata). Our efforts produced high quality and robust transcriptome assemblies validated by 1) quantifying the number of processed reads represented in the transcriptome assembly and 2) quantifying the number of highly conserved single-copy orthologs that are present in our transcript set using the BUSCO pipeline. We found 1,361 1-to-1 orthologs among the three Holbrookia species, Anolis carolinensis, and Sceloporus undulatus. We carried out dN/dS selection tests using a branch-sites model and identified a dozen genes that experienced positive selection in the Holbrookia lineage with functions in development, immunity, and metabolism. Our single-copy orthologous sequences additionally revealed significant pairwise sequence divergence (~.73%) between the Northern H. lacerata and Southern H. subcaudalis that further supports the recent elevation of the Southern Spot-Tailed Earless Lizard to full species.