Molecular zoogeography of Antarctic euphausiids and notothenioids: from species phylogenies to intraspecific patterns of genetic variation

Published and unpublished data are used to investigate possible mechanisms of species diversification in two key soups of Antarctic organisms. the Not othenioidei and the Euphausiidae. Species distributions are mapped onto mol ecular phylogenies, and this evidence is interpreted in light of the variou s ecological and historical factors which characterize the Southern Ocean. The joint effect of diverse agents (vicariance, "jump" dispersal) appears t o be determinant in several cases for species divergence. A review of resul ts from population genetics studies, together with new molecular evidence, confirm the importance of physical barriers (oceanographic fronts) in reduc ing migration, thereby promoting speciation, at least in notothenioids.