Genetic variability and divergence at 21 enzyme loci were studied in and between Italian populations of the cave spiders Nesticus eremita (13 populations), N. menozzii and N. sbordonii (one population each). The three species differ with respect to the degree of specialization to cave life, dispersion ability, isolation of populations, abundancy, extent of the distribution area, and range from the troglophilic and widespread N. eremita to the troglobitic N. sbordonii, endemic to a single cave in the Central Appennines.
Heterozygosity ranges from 0.05 to 0.15 in N. eremita populations and appears to be largely controlled by the occurrence and the extent ofgene flow among populations. The relatively low polymorphism levels of N. menozzii (H = 0.081) and N. sbordonii (H = 0.106) are also associated with reduced gene flow and small population sizes.
Genetic distances between N. eremita populations vary considerably and are strictly related to the geographical distances involved, again indicating a major role of gene flow in determining the patterns of genetic differentiation between populations. This view is strongly supported by the results of a principal component analysis applied to the gene-frequency data. Estimates of genetic divergence between species suggest that the major cladogenetic events leading to complete separation of these three Nesticus species occurred in the Middle-late Pliocene. Cave name Population Cave Municipality Province Elevation symbol register in meters number Number of individuals