Gibson, I., A. Welsh, S. Welsh, and D. Cincotta. 2018. Genetic swamping and species collapse: tracking introgression between the native Candy Darter and introduced Variegate Darter. Conservation Genetics 20:287–298. doi.org/10.1007/s10592-018-1131-2
Candy Darters (Etheostoma osburni) and Variegate Darters (E. variatum) are both native to West Virginia and Virginia. Thegeographic ranges of these two species were historically separated by Kanawha Falls, a natural barrier to fish dispersal locatedat Glen Ferris, WV. In the early 1980s, Variegate Darters or putative hybrids (E. osburni × E. variatum) were first collectedat locations upstream of Kanawha Falls, and have since undergone range expansion. Hybridization with the Variegate Darterwas one of the threats that led to the Candy Darter being listed as Endangered under the U.S. Endangered Species Act in2018. Genetic and morphologic data were examined for individuals from the New, Gauley, and Greenbrier river drainages.Individuals were genotyped using a suite of 5 diagnostic microsatellite loci to investigate potential hybridization. Widespreadhybridization was found throughout populations of Candy Darters, with the geographic range of hybridization expandingfrom 2004 to 2014. A hybrid zone was observed, with the highest levels of Variegate Darter introgression representing thekernel within this zone and the locations of first-generation (F1) hybrids at the periphery. F1 hybrids were morphologicallyintermediate within and across characters for parental species. Introgressive hybridization threatens the genetic integrity ofthe Candy Darter, and may lead to population extirpation or extinction.