Systematics and population genetics of the coldwater (Etheostoma ditrema) and watercress (Etheostoma nuchale) darters, with comments on the Gulf darter (Etheostoma swaini) (Percidae: subgenus Oligocephalus)

The current study examines members of the E. asprigene species group, particularly E. ditrema and E. nuchale, from throughout their respective ranges for products of 44 presumptive gene loci. Highly significant levels of genetic subdivision (FIT) and genetic differentiation (FST) are observed both within and between species of this group, supporting the presence of previously unrecognized diversity within this clade. Phylogenetic evaluation of polyallelic loci supports the specific recognition of E. nuchale and three taxa currently under the name E. ditrema: nominal E. ditrema (upper Coosa River system), E. sp. cf. E. ditrema (Coldwater Spring), and E. sp. cf. E. ditrema (central Coosa River system) based on either fixed allelic products or significant allele frequency differences. The Gulf darter, Etheostoma swaini, is also identified as a composite of at least three diagnosable evolutionary species, two of which (Black Warrior River system above and Cahaba River system below the Fall Line) are more closely related to E. nuchale and species of the E. ditrema complex than to remaining E. swaini. It is recommended that future conservation efforts with these highly geographically restricted and imperiled species incorporate these patterns of genetic subdivision into management and recovery plans.