GENE FLOW IN CAVE ARTHROPODS: A QUALITATIVE AND QUANTITATIVE APPROACH.

Slatkin's method (1981) for analyzing gene flow levels is applied to eleven species of cave arthropods. This provides insights into the strength of gene flow as a force affecting the evolution of cave organisms, while serving as a test of Slatkin's method. The results show that patterns of gene flow are consistent with the dispersal abilities and the ecological requirements of each species. Troglobites in general have lower gene flow values than troglophiles or trogloxenes. However, the geology of the area, its vegetation profile, and the geographic distance among the populations considered are also important in determining the gene flow levels. Gene flow patterns in three cave species, Ptomaphagus hirtus, Neaphaenops tellkampfii tellkampfii and Hadenoecus subterraneus, are compared in detail. These species inhabit the same highly interconnected karst area in south-central Kentucky but differ in their ecological requirements. The results suggest that gene flow levels are more dependent upon the intrinsic characteristics of each species than upon the availability of routes for dispersal. Overall estimates of gene flow were coupled with a more detailed population-structure analysis in four terrestrial cave arthropods: Speonomus delarouzeei, Hadenoecus cumberlandicus, Hadenoecus subterraneus and Euhadenoecus puteanus. The results stress the need for this type of analysis for subdivided species, in which estimates of the average gene flow can produce misleading results. Moreover, they show how these types of measures are more relevant in describing historical patterns of gene exchange than in indicating current levels of gene flow.