Description, Phylogenetics and Population Genetics of the Brassy Jumprock

Abstract

The Brassy Jumprock (Moxostoma sp.) is a known yet undescribed species of freshwater fish, recognized as distinct since 1956 but left without a valid name due to prolonged taxonomic confusion. The species is herein described as Moxostoma braesium, and its morphology, meristics, distribution, ecology, phylogenetic placement and population structure are documented. A total of 215 specimens were examined and compared with the morphologically similar, co-occurring, congeners M. rupiscartes and M. lachneri. Moxostoma braesium is distinguished from other co-occurring Moxostoma by the presence of 16 circumpeduncular scales and sub-plicate lips. Greater overall body depth and several meristic characters separate it from both M. rupiscartes and M. lachneri, while it can be individually separated from M. rupiscartes by shorter pectoral fins and from M. lachneri by a narrower head width. Phylogenetic relationships were inferred from RADseq SNPs under both diploid and tetraploid genotyping assumptions using maximum likelihood and Bayesian methods. Moxostoma braesium was recovered as monophyletic in all analyses and, under tetraploid assumptions, as sister to all remaining sampled Moxostoma. Population genetic analyses supported a single ancestry cluster, and the early branching position recovered is consistent with biogeographic patterns documented for other similarly distributed southern Atlantic Slope fishes.