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.

Population genetic structure of Texas horned lizards: implications for reintroduction and captive breeding.

The Texas horned lizard (Phrynosoma cornutum) inhabits much of the southern Great Plains of North America. Since the 1950s, this species has been extirpated from much of its eastern range and has suffered declines and local extinctions elsewhere, primarily due to habitat loss. Plans are underway to use captive breeding to produce large numbers of Texas horned lizards for reintroduction into areas that were historically occupied by this species and that currently have suitable habitat. We used mitochondrial markers and nuclear microsatellite markers to determine levels of genetic diversity and population structure in 542 Texas horned lizards sampled from across Texas and some neighboring states to help inform these efforts. Texas horned lizards still retain high genetic diversity in many parts of their current range. We found two highly divergent mitochondrial clades (eastern and western) and three major genetic groupings at nuclear microsatellite loci: a west group corresponding to the western mitochondrial clade and north and south groups within the eastern mitochondrial clade. We also found some evidence for human-mediated movement between these genetic clusters that is probably related to the historical importance of this species in the pet trade and as an iconic symbol of the southwestern United States. We do not know, however, if there are fitness costs associated with admixture (especially for the western and eastern clades) or if there are fitness costs to moving these lizards into habitats that are distinctly different from their ancestral areas. If present, either one or both of these fitness costs would decrease the effectiveness of reintroduction efforts. We therefore recommend that reintroduction efforts should maintain current genetic structure by restricting breeding to be between individuals within their respective genetic clusters, and by reintroducing individuals only into those areas that encompass their respective genetic clusters. This cautionary approach is based on the strong divergence between genetic groupings and their correspondence to different ecoregions.

Genetics, morphology and diet of introduced populations of the ant-eating Texas Horned Lizard (Phrynosoma cornutum).

Introduced species can diverge from their source population when they become established in a new ecosystem. The Texas Horned Lizard (Phrynosoma cornutum) is native to the western United States (US) and was historically introduced to several locations in the southeastern US. We studied three introduced populations in South Carolina, US to determine if they exhibit dietary, morphological and genetic divergence from the native western US populations. We expected little divergence from western populations because P. cornutum is a specialist whose biology is largely shaped by its diet of Pogonomyrmex harvester ants. We show that the introduced populations have mixed ancestry between south Texas and more northern areas and experienced founder effects and genetic bottlenecks resulting in decreased genetic diversity. South Carolina lizards primarily consume ants (94%), but surprisingly, they did not eat harvester ants. Introduced lizards primarily eat Dorymyrmex ants, but each introduced population complements Dorymyrmex with significantly different amounts of other species of ants, insects and plant matter. Introduced populations have smaller body size and have different limb and head shapes compared to western populations. This study demonstrates successful persistence of an introduced vertebrate that may be attributed to phenotypic change, even in the face of reduced genetic diversity.

Hematology of Free-ranging and Managed Texas Horned Lizards ( Phrynosoma cornutum).

The Texas horned lizard ( Phrynosoma cornutum) is a threatened species in Texas, US (federal category C2). Causes for population declines in this species are likely multiple. Disease and health assessments using traditional methods, including hematology, have been minimally studied in Phrynosoma spp. Apparently healthy, free-ranging Texas horned lizard from four locations in Texas ( n=53) and captive Texas horned lizards maintained at the Fort Worth Zoo ( n=16) were sampled to establish hematologic reference intervals. Within the populations studied, total leukocyte, heterophil, and eosinophil counts were higher in managed compared to free-ranging lizards. Leukocyte and heterophil counts of all lizards were lower during the ovipositional months of June and July.