Genetic structure of populations and species ofDolichopodacave crickets: evidence of peripatric divergence

Twenty-five populations of Dolichopoda cave crickets from Central-Southern Italy have been surveyed for allozyme variation at the products of 15 structural gene loci. The samples, as characterized on morphological bases, included six local populations of D. schiavazzii, one of D. aegilion, three of D. baccettii, six of D. laetitiae and nine of D. geniculata. The genetic distances between conspecific populations range from 0.014 to 0.240, those between species range from 0.054 to 0.501. The analysis of the cladogram, derived from D values, does not show a clear-cut situation within the laetitiae-geniculata group. Multivariate analyses of allele frequency data (PCA and TRGRPS) suggest that geography rather than morphology is the main factor explaining the distribution of the laetitiae-geniculata populations on the scatter diagrams. Peripheral cave populations adjacent to the Tyrrhenian and Adriatic coasts show high degrees of genetic differentiation from each other and from the inland cave populations. Most inland populations, on the other hand, appear to be genetically related, regardless of the geographic distance separating them and of the differences in epiphallus morphology. Mayr's model of peripatric speciation seems to account satisfactorily for the revealed geographic pattern of population differentiation in Dolichopoda. However the genetic mechanisms involved in this model require careful testing.