ISLAND BIOGEOGRAPHY OF NORTH EUROPEAN PARTHENOGENETIC LUMBRICIDAE .1.CLONE POOL AFFINITIES AND MORPHOMETRIC DIFFERENTIATION OF ALAND POPULATIONS

Genetic and morphometric differences between island (Aland) and mainla nd (Sweden, Finland and Estonia) populations of five parthenogenetic a nd ecologically different Lumbricidae species were studied by means of enzyme electrophoresis and morphometric analysis. Affinities of clone s to the mainland populations show that the postglacial rates of clone flow to Aland differ widely among species. In Octolasion cyaneum, the only clone found on Aland is not related to any of the studied clones from the nearby mainlands. The Aland population evidently originates from one long dispersal jump through human agency. The Aland clone poo l of the anthropochorous Aporrectodea rosea is rich. As many as 98% of the worms and 82% of the clones belong to genotypes found in the main land populations. Aland is an intergradation zone of A. rosea clones t hat have arrived From the west (Sweden) and from the east (Finland and Estonia). The more intense cultural connections to Sweden explain the higher clonal affinities that A. rosea in Aland shows to the west tha n to the east. There are not many Octolasion tyrtaeum clones on Aland. The few that are present are mainly clones also found on the mainland s. On Aland Eiseniella tetraedra has extensive diversify but low clona l affinities to the mainland populations. This also holds true for Den drobaena octaedra but clonal affinities are on an average higher than in E. tetraedra. The Aland clone pool of D. octaedra shows more affini ties to Finland than to the other mainlands. Probably the main factor that has facilitated D. octaedra clone flow from Finland is a continuo us archipelago. In most species there are at least some clones that ar e more abundant on Aland than on the mainlands. They may have a wider niche in the island environment. The Aland populations of A. rosen, O. tyrtaeum and D. octaedra differed particularly in somatic traits from the mainland populations. The secondary reproductive traits of the pa rthenogens on Aland did not differ from the mainland populations. We c onclude that except for O. cyaneum Aland has a role as a stepping ston e island in the postglacial dispersal of parthenogenetic earthworms ac ross the Baltic Sea. Different rates of flow by immigrant clones from the surrounding mainland populations have resulted in very dissimilar clone pool structures even on the same island. The Aland populations a lso show some morphometric differences to the mainland populations.