Integrative Taxonomic Investigation of Cyprinella sp. Nueces, a Putative Undescribed Species of Greatest Conservation Need in Texas

Authors: Kevin Conway, Kole Kubicek, Luke Bower, Evan Carson, Amanda Pinion, Elizabeth Hunt, David Portnoy

Year: 2022

Abstract

The Plateau Shiner (Cyprinella lepida Girard, 1856) is endemic to the upper reaches of the Nueces River drainage in TX. Previous genetic investigations of Cyprinella lepida revealed two divergent and geographically isolated groups based on mtDNA, including a group restricted to the upper Frio and Sabinal rivers (referred to as C. lepida) and a group restricted to the upper Nueces River, and more closely related to C. lutrensis than C. lepida. This later group has been referred to as either C. sp. cf. lepida or C. sp. Nueces, and is hypothesized to be the product of an ancient hybridization event between the historical upper Nueces River population of C. lepida and a lineage resembling C. lutrensis, resulting in introgression and replacement of ancestral C. lepida mtDNA in upper Nueces River. In addition to differences in mtDNA, C. lepida (Frio/Sabinal) and C. sp. Nueces (Nueces) also are reported to exhibit differences in color pattern, and the question of whether to recognize C. sp. Nueces as a distinct species has been raised on multiple occasions. Though no formal taxonomic conclusions have been published on the validity of C. sp. Nueces, this “putative” species has recently been listed as a Species of Greatest Conservation Need (SGCN) in Texas. We use a combination of qualitative osteological characters, traditional meristic characters (e.g., numbers of fin rays, scales and vertebrae) and landmark-based geometric morphometric characters to assess whether differences in morphology and body shape exist between C. lepida and C. sp. Nueces. We also, and for the first time, investigate if there are significant differences in the nuclear genome of C. lepida and C. sp. Nueces by comparing hundreds of nuclear loci obtained using double digest restriction-site associated sequencing (ddRAD-seq). We discuss our findings in relation to the question: should C. sp. Nueces be recognized as a distinct species?