Population structure, gene flow and evolutionary relationships in four species of the genera Tomocerus and Pogonognathellus (Collembola, Tomoceridae)

Genetic diversity and gene flow at 10 allozyme loci were investigated in 13 natural populations of four species of the collembolan genera Tomocerus and Pogonognathellus. Levels of observed heterozygosity were found to vary from 0.033 in P. longicornis to 0.120 in T. vulgaris. Average Nei's genetic distances (D) ranged from D=0.222 between populations of P. flavescens to D=0.647 between populations of T. vulgaris. Genetic distances between species were always >1.000 and the highest value (D=4.321) was between P. longicornis and one population of T. vulgaris. Values of FSTwere very high in all species (from 0.567 to 0.696) and levels of gene flow (Nm) derived from FSTand the private allele method were low (Nm <1). Gene flow was significantly higher only in two subsets of populations of T. vulgaris. The Plio-Pleistocenic geological rearrangements and the effect of stochastic events, such as genetic drift, are invoked to explain the different levels of genetic divergence between and within species. Distance- and character-based approaches were used to reconstruct evolutionary relationships between and within species. While the monophyly of all species was confirmed, the results did not univocally support the monophyly of the two genera, leaving the question of their generic or subgeneric status unresolved