Genetic population structure in a troglobitic beetle (Speonomus zophosinus)

Genetic variation of five variable loci was analyzed for troglobitic beetles within and between populations along the Salat and Arac Rivers in the central Pyrenees; the patterns of variation are described. Significant genetic differentiation was found for Speonomus zophosinus from populations in close proximity (10 km), largely due to differences between two groups of three populations. F_ST values range from 0.004 (Phi) to 0.354 (Est-6). Within a region, populations on opposite banks are genetically similar. Within populations genotypic frequencies were not in Hardy-Weinberg equilibrium. For troglobitic species such as S. zophosinus, gene flow is a function of intrinsic (active movement and reproductive strategy) and extrinsic factors (geologic structure of the subterranean environment). It seems that natural selection has played little, if any, role in generating the observed gene frequency patterns. The patterns of variation are most reasonably explained as having resulted from genetic dirft occurring between two areas separated by an inhospitable habitat which acts as a dispersal barrier or limits gene flow.