Increased habitat fragmentation leads to isolation among and low genetic diversity within populations of the imperiled Kentucky Arrow Darter (Etheostoma sagitta spilotum)

Abstract

The Kentucky Arrow Darter (Etheostoma sagitta spilotum) is federally listed as threatened and known only from five tributary systems in the Kentucky River system, Kentucky, USA. Recent surveys revealed considerable population decline, with individuals detected in only 45% of known historical localities. Impacts of these declines on the genetic structure of E. s. spilotum may be exacerbated by limited dispersal capabilities and small initial population size resulting in high levels of isolation among extant populations. Long standing genetic isolation may also be evident in contemporary genetic signatures; populations that have undergone historic isolation may be prime candidates for intensive conservation efforts. To address contemporary and historic genetic isolation, we generated genotypic (11 microsatellite loci) and mtDNA sequence (ND2 gene) data from multiple locations spanning the taxon’s range. We recovered seven haplotypes with low divergence levels, shared among and within multiple Kentucky River tributary systems, indicating absence of long-standing isolation among localities examined. In contrast, microsatellite data suggested all nine populations are functionally isolated, with little to no admixture among populations, even among those within the same tributary system. The drastic decline of E. s. spilotum populations has likely combined with limited dispersal, resulting in extensive contemporary genetic isolation among extant populations. Conservation management plans to enhance stability and maintain survivability of E. s. spilotum must address the severe genetic isolation identified here and work towards increasing gene flow among extant populations.