Comparative mitochondrial genetic investigation of three lower Rio Grande endemic species of freshwater fishes

Authors: Kevin Conway, Amanda Pinion, Audrey Carlos, David Portnoy

Year: 2019

Abstract

The arid southwestern United States is home to many endemic freshwater fishes. The majority of these species are patchily distributed across this desert landscape and are experiencing range-wide declines due to habitat degradation, aridification through ground water depletion, and the introduction of non-native species. Though several of these desert fishes are already offered protection under the US Endangered Species Act and are relatively well-studied, many desert fishes are not yet protected at State or Federal levels and basic information that would aid conservation assessment (e.g., estimate of genetic diversity) is not currently available. This is the case for three species of freshwater fishes endemic to the lower Rio Grande drainage of south central Texas and northern Mexico: Cyprinella proserpina, Notropis megalops (Cyprinidae), and Etheostoma grahami (Percidae). We investigated levels of mitochondrial DNA diversity (multiple loci) within and between multiple TX populations (ranging from 4-6) of the three aforementioned species to provide baseline genetic data for future conservation assessment and management. Haplotype diversity (h) was generally low at sample locations for each of the three species (0-0.6786 for C. proserpina, 0.2-0.8333 for N. megalops and 0-0.6667 for E. grahami). A suite of standard conservation genetic statistics (including Pairwise Fst and AMOVA) support that idea that each of the three species comprises multiple populations that appear to be isolated from each other (though there is a lack of precise in some estimates due to small sample sizes). Low levels of genetic diversity and isolation are a bad combination but appear to be the norm for freshwater fishes of the Trans-Pecos. Additional work with nuclear markers and larger sample sizes will be needed to estimate effective population size and inbreeding coeficients for populations of each of the three species. These basic data will be important for the future conservation management of these relatively poorly studied lower Rio Grande endemic fishes.