Assessment of genomic diversity within and between two cryptic shiners, the West Texas shiner (Notropis megalops) and the Texas shiner (Notropis amabilis).

Abstract

The presence of cryptic species can hinder effective conservation planning and implementation, as has been the case for speciose groups of freshwater fishes that are difficult to differentiate due to conserved morphologies. The West Texas shiner Notropis megalops and the Texas shiner Notropis amabilis are a cryptic pair of leuciscids (minnows) that co-occur in spring-fed tributaries of the Rio Grande in Texas and Mexico. Both N. megalops and N. amabilis are listed as Species of Greatest Conservation Need by the Texas Parks and Wildlife Department. Notropis amabilis is widespread and listed as apparently secure by Texas Parks and Wildlife Department whereas N. megalops has a very limited distribution and has not been ranked by Texas Parks and Wildlife Department because of data deficiency. Morphological differences between these species have been described; however, proper identification in situ remains problematic. Furthermore, given their range of overlap there is potential for hybridization, and limited genetic data have been collected comparing the species. Therefore, reduced representation genomic and mitochondrial sequencing data were used to reassess the distinctness of the species, screen for hybridization, and characterize their relative frequencies throughout their range of overlap. Genomic analyses recovered two distinct genetic groups corresponding to the species (F'_CT = 0.89) with no evidence of admixture or introgression. The species were found to co-occur at three sampling locations, two in the Devils River and one in the Pecos, but not in equal frequencies. Overall, these results provide data and tools for further research on N. megalops needed for accurate conservation policies and management practices.