GEOGRAPHICALLY STRUCTURED GENETIC DIVERSITY IN THE CAVE BEETLE DARLINGTONEA KENTUCKENSIS VALENTINE 1952 (COLEOPTERA, CARABIDAE, TRECHINA)

This study assesses genetic diversity in the monotypic cave carabid beetle genus Darlingtonea using mitochondrial DNA to test the relationship between putative geographical barriers to subterranean dispersal and the boundaries of genetically distinct groups at two scales: major watersheds and higher order streams. The mitochondrial gene cytochrome oxidase I (COI) was sequenced for up to four individuals from each of 27 populations, sampled from caves along the interface of the Mississippian and Cumberland plateaus in eastern Kentucky and northern Tennessee, USA, yielding 28 unique haplotypes. Hierarchical analyses of molecular variance (AMOVA) within and among geographically defined groups tested two a priori hypotheses of structure based on major and minor river drainages, as well as genetic distance clusters defined a posteriori from an unrooted analysis of all 85 individuals. High genetic differentiation (F_ST) between populations was found across analyses. The influence of isolation by distance could potentially account for much of the variation found among geographically defined groups at both levels. High variability among the three northernmost genetic clusters (F_CT), low variability among populations within clusters (F_SC), and low within-cluster Mantel correlations indicate the importance of unidentified barriers to gene flow separating closely grouped caves. Overall phylogeographic patterns are consistent with previous evidence of population isolation among cave systems in the region, revealing geographically structured cryptic diversity in Darlingtonea over some of its range. The landscape features considered a priori in this study were not predictive of the genetic breaks among the three northern clusters, which are genetically distinct despite their close geographic proximity.