SPATIAL RELATIONSHIP AND GENE FLOW PATHS BETWEEN POPULATIONS OF THE ALPINE SNAIL ARIANTA-ARBUSTORUM (PULMONATA, HELICIDAE)

This species was sampled along an 8 km contour line in the Swiss Alps orthogonal to altitudinal clines in life history and shell traits. Allele frequencies are best explained by the spatial structure whereas the morphs are better explained by the habitats. The genotypic distances point to a historical explanation by recolonization processes, the phenotypical dissimilarities to a selectionist interpretation of the present distribution of the populations. The following conclusions are from the study of the spatial relationship and the gene flow paths for A. arbustorum at Mount Martegnas: 1) Streams are the main gene flow paths; gene flow is low, allowing differentiation of local populations; 2) Morphs and habitats are correlated, but the interpretation has to be made carefully. The spatial dependence of habitats has to be included into the analysis of selection. 3) The random assumption for gene flow is not a spatial isolation-by-distance model, but a functional isolation-by-distance model, assuming gene flow over the drainage system. -from Author