Molecular Phylogeny of the Snubnose Darters, Subgenus Ulocentra (Genus Etheostoma, Family Percidae)

Abstract

Snubnose darters comprise one of the largest subgenera of the percid genus Etheostoma. Many species are described based on differences in male breeding coloration. Few morphological synapomorphies have been proposed for the subgenus and their relatives, making it difficult to delineate monophyletic clades. The phylogenetic relationships of the 20 snubnose darter species of the subgenus Ulocentra and 11 members of its proposed sister subgenus Etheostoma were investigated with partial mitochondrial DNA sequences including 1033 bp encompassing the entire mitochondrial control region, the tRNA-Phe gene, and part of the 12S rRNA gene. Two hypotheses on the relationship and monophyly of the two subgenera were evaluated. Both maximum-parsimony and neighbor-joining analyses supported monophyly of the subgenus Ulocentra and resolved some species-level relationships. The banded darter, E. zonale, and its sister taxon, E. lynceum, were not closely related to the snubnose darters and appear to be diverged from the other members of the subgenus Etheostoma, fitting their former distinction as the recognized subgenus Nanostoma. The sister group to Ulocentra appears to be a restricted species assemblage within the subgenus Etheostoma containing E. blennioides, E. rupestre, E. blennius, and the E. thalassinum species group. The placement of the harlequin darter, E. histrio, is problematic, and it may represent a basal member of Ulocentra or of the restricted subgenus Etheostoma. Despite recent estimates of divergence times between nominal Ulocentra taxa, each species exhibits its own unique set of mtDNA haplotypes, providing no direct evidence for current genetic exchange between species. The nominal taxa of snubnose darters thus appear to be evolving independently from each other and therefore constitute valid species under the Phylogenetic Species Concept.