Allozyme variation in the springtails Allacma fusca and A. gallica (Collembola, Sminthuridae)

SummaryCollembola is a group of soil arthropods whose ecophysiological requirements tend to promote inter-population isolation and genetic differentiation. To test this, we analysed the genetic structure of 22 populations of two species of the genus Allacma (A. fusca and A. gallica), using allozyme electrophoresis. Several loci showed distinct differences between the two species, and high levels of genetic divergence (Nei's D=1.144±0.130) were found between them; in addition, the average genetic distance among populations was low in A. fusca (D=0.050±0.034), but considerably higher among those of A. gallica (D=0.435±0.342). The two species were significantly different in average heterozygosity with A. gallica (He=0.062) being more variable than A. fusca (He=0.028). Wright's FST statistics, based on polymorphic loci, indicate that the two species are subdivided into genetically heterogeneous populations, with A. gallica being more differentiated (FST=0.873) than A. fusca (FST=0.533). The observed divergence between and within the two species may result from the absence of gene flow and subsequent allopatric differentiation through genetic drift. In addition, ecological and geological factors may explain the origin of such a differentiation, while the peculiar mode of reproduction may influence the levels of intra-population genetic variability.