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Abstract

1. Only a few studies have compared patterns of genetic variation among populations of different Daphnia species on a regional scale. The present study addresses this gap and examines the relationship between diversity as revealed by allozyme variation and habitat size for populations of Daphnia pulex, D. obtusa and D. curvirostris in Flanders ( Belgium). In addition, we examined whether patterns of isolation-by-distance could be observed in each of these three Daphnia species. 2. The relationship between genetic diversity and habitat size varied among Daphnia species that occur in the same region. In D. pulex and D. obtusa populations, a positive relationship between local genetic diversity and habitat size was found, whereas the relationship was negative in D. curvirostris populations. 3. Regional genetic diversity was lower than expected from patterns of local genetic diversity in D. pulex and D. obtusa populations in Flanders. This suggests that the subdivision of local Daphnia populations in a region did not obviously increase genetic diversity. 4. Genetic differentiation among populations of these three species in Flanders was moderate and comparable with values observed in other Daphnia species. Patterns of isolation-by-distance could be observed, but the scatter was high ( D. pulex) or the slope was very low (D. obtusa).