Evolution of the Cyprinella lutrensis Species-Complex. II. Systematics and Biogeography of the Edwards Plateau Shiner, Cyprinella lepida

Abstract

We examined geographic samples of the Edward's Plateau shiner, Cyprinella lepida, for restriction site variation of mitochondrial (mt)DNA. Sixteen restriction endonucleases were used to assay mtDNAs from 32 individuals of C. lepida sampled from the three rivers (Nueces, Frio, and Sabinal) of the Nueces River basin. Maximum-parsimony analysis using Cyprinella lutrensis as the outgroup and Cyprinella venusta as the root revealed that C. lepida in the Frio and Sabinal rivers is distinct from C. lepida in the Nueces River. A tree generated from a matrix of genetic distance using the Fitch-Margoliash method also revealed the same two distinct lineages of Cyprinella within the Nueces River basin. Percentage nucleotide sequence divergence estimates (? SE) between pairwise comparisons of the two evolutionary lineages of Cyprinella in the Nueces River basin and C. lutrensis were as follows: 8.36 ? 0.01 (Cyprinella in the Frio and Sabinal rivers vs C. lutrensis), 9.04 ? 0.03 (Cyprinella in the Frio and Sabinal rivers vs Cyprinella in the Nueces River), and 9.52 ? 0.03 (Cyprinella in the Nueces River vs C. lutrensis). Assuming mtDNA mutation-rate equivalency within Cyprinella, the two lineages (species) of Cyprinella in the Nueces River basin could have evolved nearly instantaneously in geological time. The estimates of mtDNA nucleotide sequence divergence, in concert with geographic considerations and the assumption that the genus Cyprinella originated north of the Coastal Plain, are consistent with the hypothesis that the ancestor(s) to the lineages of Cyprinella in the Nueces River basin entered the western (Gulf) Coastal Plain preglacially and from the northwest.