CLONAL AND MORPHOLOGICAL VARIATION IN MARGINAL POPULATIONS OF PARTHENOGENETIC EARTHWORMS OCTOLASION-TYRTAEUM AND O-CYANEUM (OLIGOCHAETA, LUMBRICIDAE) FROM EASTERN FENNOSCANDIA

Clone pool diversity was studied in two parthenogenetic Octolasion spe cies in South Finland belonging to the region of Fennoscandia where th e species occur at the northern margin of their European range. In spo ntaneously dispersing O. tyrtaeum we recorded 24 clones (238 individua ls/8 localities), but in anthropochorously dispersing O. cyaneum only two clones (134 ind./4 locs.) were found. In O. tyrtaeum the clone poo ls of the East (= sample region) and the North were more similar to ea ch other than to that in the West. Clone groups showed a clinal distri bution pattern, which suggests that they may be adapted to regional en vironments. The low clonal heterogeneity of O. cyaneum is attributed t o a small founder population and clonal drift. Morphological variabili ty showed that characters related to reproductive organs vary extremel y little in the two species. Considering somatic characters, segment n umber seemed to be mostly controlled by the genotype, whereas body siz e varied mostly according to the locality and region implying the role of environmental variables. In the North, O. tvrtaeum adults were lar ger than their counterparts in the East and the West.