GENETIC-STRUCTURE OF COEXISTING SEXUAL AND CLONAL SUBPOPULATIONS IN AFRESH-WATER SNAIL (POTAMOPYRGUS-ANTIPODARUM)

We examined clonal diversity and the distribution of both clonal and s exual genotypes in a single population of freshwater snails (Potamopyr gus antipodarum) in which diploid sexual individuals and triploid part henogens coexist. A genetic analysis of individuals from three habitat zones in Lake Alexandrina, New Zealand revealed extremely high clonal diversity: 165 genotypes among 605 clonal individuals. The frequency of triploid clonal individuals increased with increasing depth in the lake, and most of the individual clones were habitat specific, suggest ing that differences among habitats are important in structuring the c lonal subpopulation. There were also high levels of clonal diversity w ithin habitats, suggesting frequent origins of habitat-specific clones . In contrast, diploid sexual individuals were proportionately more co mmon in the shallow regions of the lake (where infection by trematode larvae is highest), and there was no significant spatial structure in the sexual subpopulation. We suggest that habitat specialization by cl ones, as well as parasite-mediated selection against common clones, ar e important factors affecting the structure of this mixed population o f sexual and clonal snails.