Geographic and Temporal Diversification Patterns in the Barcheek Darter Species Group

The purpose of this study was to investigate geographic and temporal diversification patterns in the barcheek darter species group. Specifically, my two questions were “Is there geographical structure of alleles or haplotypes within currently recognized species that is suggestive of unrecognized, or cryptic, species diversity within the clade?” (geographic diversification pattern) and “How old are inter- and intraspecific divergence events in the evolutionary history of the clade?” (temporal diversification pattern). A three gene dataset from 159 barcheek individuals of two mitochondrial coding regions, cyt b and ND2, along with a nuclear intron, S7, was analyzed using parsimony and Bayesian phylogentic methods to answer the first question. Divergence times were estimated using fossil calibration of this Bayesian phylogeny in order to answer the second question. Three barcheek species were found to have significant population structure suggestive of cryptic species diversity. E. basilare in particular was recovered as being comprised of five reciprocally monophyletic clades endemic to each of the major tributaries to the upper Caney Fork River. Inter- and intraspecific divergence events were found to be relatively old in the clade, nearly all pre-Pleistocene, with a crown node age estimated at 12.68 mya. These results are discussed in light of the present understanding of the tempo of diversification in the darter radiation.