MITOCHONDRIAL-DNA POLYMORPHISM AMONG ALPINE POPULATIONS OF GAMMARUS-LACUSTRIS (CRUSTACEA, AMPHIPODA)

1. Mitochondrial DNA sequence analysis was used to investigate the phy logeographic structure among populations of the amphipod Gammarus lacu stris isolated in high altitude lakes from the Northern to the Souther n Alps, and to investigate the historical and demographic events that may have accompanied this differentiation. 2. The comparison of a 376- base segment of the mitochondrial cytochrome c oxidase I gene in fifty -four specimens from nine different populations reveals no variation w ithin populations. However, northern populations appear divergent from those from the Southern Alps. A particular population, located at the limit between the Northern and Southern Alps shows an intermediate ha plotype related to the southern lineage. 3. Consideration of the diffe rent mitochondrial lineages, together with geographical differences am ong populations, suggests a scenario for the post-glacial colonization of G, lacustris in the alpine lakes.