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 an d Pogonognathellus. Levels of observed heterozygosity were found to vary Fr om 0.033 in P. longicornis to 0.120 in T. vulgaris. Average Nei's genetic d istances (D) ranged from D = 0.222 between populations of P. flavescens to D = 0.647 between populations of T. vulgaris. Genetic distances between spe cies were always >1.000 and the highest value (D = 4.321) was beween P. lon gicornis and one population of T. vulgaris. Values of F-ST were very high i n all species (from 0.567 to 0.696) and levels of gene flow (Nm) derived fr om F-ST and the private allele method were low (Nm < 1). Gene flow was sign ificantly higher only in two subsets of populations of T. vulgaris. The Pli o-Pleistocenic geological rearrangements and the effect of stochastic event s, such as genetic drift: are invoked to explain the different levels of ge netic divergence between and within species. Distance- and character-based approaches were used to reconstruct evolutionary relationships between and within species. While the monophyly of ail species was confirmed, the resul ts did not univocally support the monophyly of the two genera, leaving the question of their generic or subgeneric status unresolved. (C) 2000 The Lin nean Society of London.