Island biogeography of North European parthenogenetic Lumbricidae: I. Clone pool affinities and morphometric differentiation of Åland populations



Genetic and morphometnc differences between island (Åland) 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 Åland differ widely among species In Octolasion cyaneum, the only clone found on Åland is not related to any of the studied clones from the nearby mainlands The Åland population evidently originates from one long dispersal jump through human agency The Åland 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 Åland 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 Åland shows to the west than to the east There are not many Octolasion tyrtaeum clones on Åland The few that are present are mainly clones also found on the mainlands On Åland Eisemella tetraedra has extensive diversity 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 Åland than on the mainlands They may have a wider niche in the island environment The Åland populations of A rosea, O tyrtaeum and D octaedra differed particularly in somatic traits from the mainland populations The secondary reproductive traits of the parthenogens on Åland did not differ from the mainland populations We conclude that except for O cyaneumÅland 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 Åland populations also show some morphometric differences to the mainland populations