Estimating levels of gene flow between natural populations in the genus Isotomurus (Collembola, Isotomidae)

A study on the genetic structure of six European species from the genus Isotomurus is presented, with special attention to the levels of gene flow between populations. An indirect estimate of gene flow (Nm) among populations was obtained from allozyme frequencies using two theoretical demic models. In spite of the reduced vagility of the specimens and of the relatively wide range of sampling locations, levels of gene flow within the six species investigated were rather variable. Some species or groups of populations are morphologically and genetically very homogeneous, even when geographic distances between sampling locations are large. Other populations, often geographically more isolated, show a considerable degree of differentiation, with relatively high values of genetic distance and fixation for degrees of intraspecific differentiation highlight the importance of historical and geographic factors in determining gene flow levels. The analysis is complicated by the presence of genetically strongly differentiated conspecific populations, whose taxonomic status must probably be reconsidered