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Abstract

Within the species complex of Daphnia galeata, D. cucullata and D. hyalina various combinations of hybrids and parental taxa occur in lakes throughout Europe. Since daphnids are cyclic parthenogens and mostly reproduce asexually, hybrid populations can be maintained by asexual reproduction and without recurrent hybridization events. Therefore, it is possible that hybridization events have been rare, with range expansion occurring by dispersal of hybrids.

Allozyme data from seven European populations were used to compare genetic variation within and between hybrid and parental taxa. An UPGMA cluster analysis of genetic distances showed that D. cucullata x galeata hybrids from different lakes grouped in different clusters according to the lake from which they were isolated, suggesting multiple hybridization events. Clonal diversity within hybrid taxa was comparable to parental taxa. Furthermore, evidence was found for introgression of the Pgi-S allele from D. cucullata to D. galeata in three lakes. These results indicate that multiple hybridization events within this species complex are likely, and that hybrid taxa can reproduce sexually.