TRACKING DISPERSAL ROUTES - PHYLOGEOGRAPHY OF THE ARCTIC ANTARCTIC DISJUNCT SEAWEED ACROSIPHONIA-ARCTA (CHLOROPHYTA)

Phylogenetic relationships in the Arctic-Antarctic disjunct seaweed sp ecies Acrosiphonia arcta (Dillwyn) J. G. Agardh (Acrosiphoniales, Chlo rophyta) were examined using restriction fragment-length polymorphism analysis of the fast-evolving nuclear ribosomal intergenic spacer (IGS ) region and random amplified polymorphic DNA (RAPD) markers. Twenty-t wo isolates collected from 10 different locations in both hemispheres were compared. Five IGS length classes were identified among the 10 lo cations. Throughout the North Atlantic, IGS regions were found to be e xtremely homogeneous whereas RAPD patterns revealed subdivided populat ions that suggest founder effects. Acrosiphonia arcta populations foun d in the Arctic and North Atlantic oceans are hypothesized to be of Pa cific origin. Extensive differences found between Arctic Greenland pop ulations and those in the North Atlantic suggest that colonization of Arctic Greenland occurred as an independent event. Recolonization of t he Antarctic peninsula from Southern Chile is favored, whereas the dir ectionality of transequatorial passage along the western coast of the Americas could be in either direction.