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 mainland (Sweden, Finland and Estonia) populations of five parthenogenetic and ecologically different Lumbricidae species were studied by means of enzyme electrophoresis and morphometric analysis. Affinities of clones 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 pool 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 mainland populations. Aland is an intergradation zone of A. rosea clones that 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 than to the east. There are not many Octolasion tyrtaeum clones on Aland. The few that are present are mainly clones also found on the mainlands. On Aland Eiseniella tetraedra has extensive diversify but low clonal affinities to the mainland populations. This also holds true for Dendrobaena octaedra but clonal affinities are on an average higher than in E. tetraedra. The Aland clone pool of D. octaedra shows more affinities to Finland than to the other mainlands. Probably the main factor that has facilitated D. octaedra clone flow from Finland is a continuous archipelago. In most species there are at least some clones that are 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 parthenogens on Aland did not differ from the mainland populations. We conclude that except for O. cyaneum Aland has a role as a stepping stone island in the postglacial dispersal of parthenogenetic earthworms across 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 also show some morphometric differences to the mainland populations.