Low genetic diversity and evidence of population structure among subspecies of Nerodia harteri, a threatened water snake endemic to Texas

Abstract

Nerodia harteri is a threatened small-bodied water snake that occupies one of the most restricted ranges of any snake within the continental United States. It is found closely associated with rivers and tributaries in the Colorado and Brazos river basins, which flow through north-central Texas. Nerodia harteri has been at the center of debate owing to conflicts between conservation efforts and the construction of dams that change or destroy its preferred habitat. Additionally, its taxonomic status has also been under contention with some authors recognizing two subspecies, the Brazos water snake (N. h. harteri) and the Concho water snake (N. h. paucimaculata), whereas other authors consider each separate species. Despite its relatively recent discovery during the 1940s, N. harteri has been the subject of several ecological studies, yet no population genetic assessment of either subspecies has been performed to date. We first evaluated the phylogenetic placement of both subspecies among other North American Nerodia using partial sequence data from the mitochondrial gene cytochrome-b. We then tested for population subdivision among four rivers encompassing the range of N. harteri and tested for the presence of admixture between river basins using mitochondrial sequence data (920 bp of cyt-b) and five cross-species amplified microsatellite loci. We found low mitochondrial haplotype diversity represented by two unique haplotypes in each river basin, which were separated by no more than four nucleotide changes. Nuclear loci showed low genetic diversity and population structuring within and among river basins. We did not find conclusive evidence of admixture between basins, and we support the presence of two separate evolutionarily significant units and two separate management units corresponding to each major river basin. Given increasing natural and anthropogenic threats, we recommend continued ecological and genetic monitoring of both subspecies.

Comparative host-pathogen dynamics of Snake Fungal Disease in sympatric species of water snakes (Nerodia)

“…Consequently, achieving captures at a rate needed to confer narrow confidence intervals for Oo prevalence estimates is difficult for relatively rare species like N. h. harteri . Yet, the number of N. h. harteri we captured during our survey ( N = 40) was consistent with previous population surveys conducted over similar time intervals 31,34 ; therefore, uncertainty of Oo prevalence estimates could also be remedied by long-term surveillance efforts for this taxon.…”

“…Combined with a moderately high prevalence of Oo (47.4% overall, Table 1), this finding highlights the need for continued Oo surveillance and renewed conservation action planning. Previous studies have shown that both subspecies of N. harteri have low genetic diversity, and N. h. paucimaculata populations exhibit bottleneck signatures 31,57 . The application of additional sampling and genetic markers are needed, however, to facilitate robust tests for population contractions and their timing in N. harteri 31,57 .…”

“…Previous studies have shown that both subspecies of N. harteri have low genetic diversity, and N. h. paucimaculata populations exhibit bottleneck signatures 31,57 . The application of additional sampling and genetic markers are needed, however, to facilitate robust tests for population contractions and their timing in N. harteri 31,57 . For instance, spatial ecology studies have shown N. h. paucimaculata can exhibit high site fidelity and are unlikely to move more than 1 km unless driven by stochastic factors such as variable water flow 33 .…”

Genetic Diversity and Population Structure of the Hotoke Loach, Lefua echigonia, a Japanese Endangered Loach

“…8). Considering the geographical locations of the populations as performed in the previous studies [85][86][87][88], Cluster I mainly indicated to be the genetic population of the lower part of the Kokai including the Oh and Sakura Rs (Fig. 9).…”

Genetic variability, management, and conservation implications of the critically endangered Brazilian pitviper Bothrops insularis

“…Conservation studies and efforts have been predominantly focused on endangered species (McLennan et al., 2018; Reynolds et al., 2015; Rodriguez et al., 2012). Accordingly, this study is a contribution to the conservation program of B. insularis , a critically endangered Brazilian snake, for which we describe the first genetic diversity framework of a wild and a captive population.…”