Systematics of the Riffle Dace with Special Emphasis on the Blacknose Daces (Leuciscidae: Rhinichthys)

Abstract

The freshwater fish genus Rhinichthys (Agassiz 1849) has a complex taxonomic history and extensive geographic distribution across North America. In this dissertation, I used multiple molecular and morphological approaches to resolve taxonomic uncertainties and understand evolutionary relationships within this genus. Multi-locus phylogenetic analysis using Bayesian Inference revealed three major clades within Rhinichthys: R. atratulus, R. cataractae, and R. osculus clades. Widespread species were found to be non-monophyletic due to misidentifications and local endemic populations recovered within broader species complexes. Restriction site-associated DNA sequencing (3RAD) analyses of the Eastern Blacknose Dace (R. atratulus) and Western Blacknose Dace (R. obtusus) revealed three distinct evolutionary lineages with strong phylogenomic support: R. atratulus, R. obtusus A, and R. obtusus B (potentially R. meleagris). The distribution of R. obtusus B in predominantly glaciated regions versus R. obtusus A in non-glaciated regions suggests distinct evolutionary histories tied to glacial refugia and subsequent recolonization patterns. Despite their genetic distinctiveness, geometric morphometric analysis demonstrated that the Eastern and Western Blacknose Dace species are morphologically indistinguishable. Principal component analysis revealed no significant differences, though canonical variate analysis did differentiae the species, although the differences are not likely diagnostic. When focusing on R. obtusus populations within Alabama, a biogeographic study focused on populations in the Black Warrior River system of the Mobile Basin revealed multiple independent movements between the Tennessee River Drainage and the Mobile River Basin. Phylogenomic analysis recovered two separate, monophyletic clades that are not each other’s closest relatives, with variable gene flow recovered across systems. These findings suggest that R. obtusus was likely never fully extirpated from the Black Warrior River despite previously suggested. Overall, this dissertation highlights the complex evolutionary relationships of Rhinichthys and demonstrates the values of combining multiple molecular and morphological approaches to better resolve intricate relationships. My dissertation not only addresses key questions but also opens new areas for exploring evolutionary patterns within this diverse genus of North American freshwater fishes.