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 species in South Finland belonging to the region of Fennoscandia where the species occur at the northern margin of their European range. In spontaneously dispersing O. tyrtaeum we recorded 24 clones (238 individuals/8 localities), but in anthropochorously dispersing O. cyaneum only two clones (134 ind./4 locs.) were found. In O. tyrtaeum the clone pools of the East (= sample region) and the North were more similar to each other than to that in the West. Clone groups showed a clinal distribution pattern, which suggests that they may be adapted to regional environments. The low clonal heterogeneity of O. cyaneum is attributed to a small founder population and clonal drift. Morphological variability showed that characters related to reproductive organs vary extremely little in the two species. Considering somatic characters, segment number seemed to be mostly controlled by the genotype, whereas body size varied mostly according to the locality and region implying the role of environmental variables. In the North, O. tvrtaeum adults were larger than their counterparts in the East and the West.