Population structure of Hydropsyche exocellata. Genetic homogeneity in a zone of fragmented distribution

Using four allozymic loci, we analysed the genetic structure and differenti ation of Hydropsyche exocellata (Trichoptera; Hydropsychidae) larvae in sev en sites along the Upper Loire River (France). The genetic differentiation is low for this species despite distribution patchiness, and only due to on e locus in one study site. No trend relating genetic differentiation to geo graphic distance (isolation by distance) was observed. Significant deviatio ns from Hardy-Weinberg equilibrium were observed at most sites and loci. Th e population genetics analysis of an amphibiotic insect such as H. exocella ta in light of current ecological and population genetics knowledge is disc ussed following two main factors: 1) sampling of partially reproductively i solated, genetically distinct subpopulations, and 2) form of selection. Des pite knowledge on several aspects of the ecology of H. exocellata in the Ri ver Loire, numerous points limit genetic data interpretation. These points are underlined and discussed with reference to studies on other amphibiotic insects. (C) 2000 Academie des sciences/Editions scientifiques et medicale s Elsevier SAS.