Systematics and biogeography of Cyprinella venusta (Cyprinidae: Teleostei) inferred from analysis of mitochondrial DNA

Abstract

Mitochondrial (mt)DNA restriction-site analysis was used to study systematics and biogeography of the blacktail shiner, Cyprinella venusta. Taxonomically, C. venusta is comprised of three subspecies: C. v. venusta, C.v. cercostigma, and C. v. stigmatura. Phylogenetic analyses of mtDNA restriction-sites assayed from 20 geographic populations of C. venusta collected throughout the range of the species employed maximum parsimony, Neighbor-joining, and UPGMA cluster analysis. Cyprinella galactura and Cyprinella lutrensis were used as outgroups for the analyses. Maximum parsimony analysis revealed three major phylogeographic clades: these were termed Apalachicola, Mobile, and Western clades. The Western clade included four distinct lineages, termed PearlPascagoula, Mississippi, East Texas, and West Texas lineages. Blacktail shiners collected from the range of C. v. stigmatura formed the Mobile clade; the Pearl Pascagoula lineage and Apalachicola clades were comprised of lineages of blacktail shiners collected from the range of C. v. cercosticrma; and the Mississippi, East Texas and West Texas lineages were comprised of lineages of blacktail shiners from the range of C. v. enusta. The clades and lineages exhibited an east to west pattern of divergence across the Gulf Coastal Plain. The Apalachicola clade was most basal and sister the Mobile clade and the Western clade. Neighbor-Joining and UPGMA clustering generally supported results from maximumparsimony analysis. Results of phylogenetic analyses, combined with estimates of mtDNA nucleotide-sequence divergence among clades, indicated that-C. enusta was present in the southeastern United States during late Miocene-early Pliocene times. Subsequent (sequential) divergences were the Apalachicola clade (during the early Pliocene), Mobile clade (during the mid-Pliocene), and lineages within the Western clade (during the late Pliocene-early Pleistocene). Isolation of the four lineages within the Western clade may correspond to elevated levels of the Gulf of Mexico during the late Pliocene and early Pleistocene. observed phylogeographic discontinuities involved the Apalachicola and Mobile Bay drainages, and correspond to previously hypothesized zones of vicariance. The Apalachicola, Mobile, and Western clades merit elevation to species status.