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

Dean A Williams,Amanda M Hale,Nathan D Rains

doi:10.7717/peerj.7746

Dean A Williams, Amanda M Hale + Show 1 more

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https://doi.org/10.7717/peerj.7746

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Abstract

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.

Highlights

The loss of suitable native habitat to agriculture and urbanization, and the overexploitation of populations have been the largest drivers of the decline of many species (Maxwell et al, 2016)
We found no evidence for separate mitochondrial clades corresponding to the north and south populations detected by STRUCTURE
The western mitochondrial clade and population is found in the Chihuahua desert ecoregion, whereas the eastern mitochondrial clade can be subdivided into two nuclear DNA populations that correspond to a north cluster found in the South-Central Semi-Arid Prairies ecoregion (EPA level II) and a south cluster found in the South Texas Plains, East-Central Texas Plains, and Western Gulf Coastal Plain

Summary

Introduction

The loss of suitable native habitat to agriculture and urbanization, and the overexploitation of populations have been the largest drivers of the decline of many species (Maxwell et al, 2016). Reintroduction and reinforcement programs try to reduce these effects by returning a species to an area from which it became locally extinct or by increasing the numbers of individuals in small populations (IUCN, 2013; Seddon, 2010). A sufficient number of individuals with high genetic diversity should be utilized in these efforts to reduce the potential for inbreeding depression and enhance the ability of a population to adapt to changing environmental conditions (Johnson et al, 2010; Carlson, Cunningham & Westley, 2014; Jamieson, 2015). Captive breeding programs can potentially be used to raise large numbers of individuals for these reintroduction efforts and are subject to many of the same genetic considerations as reintroductions (Ebenhard, 1995; Williams & Osentoski, 2007; Attard et al, 2016). Understanding the population genetic structure of a species can inform these efforts by identifying appropriate source populations, defining management units, and identifying populations that have high genetic diversity (Weeks et al, 2011; Attard et al, 2016)

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