HYBRIDIZATION IN THE DAPHNIA-GALEATA COMPLEX - ARE HYBRIDS LOCALLY PRODUCED

Within the species complex of Daphnia galeata, D. cucullata and D. hya lina various combinations of hybrids and parental taxa occur in lakes throughout Europe. Since daphnids are cyclic parthenogens and mostly r eproduce asexually, hybrid populations can be maintained by asexual re production and without recurrent hybridization events. Therefore, it i s possible that hybridization events have been rare, with range expans ion occurring by dispersal of hybrids. Allozyme data from seven Europe an populations were used to compare genetic variation within and betwe en hybrid and parental taxa. An UPGMA cluster analysis of genetic dist ances showed that D. cucullata x galeata hybrids from different lakes grouped in different clusters according to the lake from which they we re isolated, suggesting multiple hybridization events. Clonal diversit y within hybrid taxa was comparable to parental taxa. Furthermore, evi dence was found for introgression of the Pgi-S allele from D. cucullat a to D. galeata in three lakes. These results indicate that multiple h ybridization events within this species complex are likely, and that h ybrid taxa can reproduce sexually.