GENETIC-EVIDENCE OF WIDESPREAD DISPERSAL IN A PARTHENOGENETIC FRESH-WATER OSTRACOD

We used an hierarchical analysis of allozyme variation to investigate for the freshwater ostracod Candonocypris novaezelandiae the relative contributions of sexual and asexual reproduction to recruitment into 4 2 local populations and to infer patterns of gene flow within and amon g four geographical regions (watersheds) in south-eastern Australia. A llele frequency variation among local populations was marked (mean F-S T - 0.228) but showed no regional differentiation. The allele frequenc y differences among local populations probably reflect the effects of stochastic processes, such as founder events, as well as variation in the success, and hence abundance, of particular clonal genotypes withi n water-bodies. Indeed, local populations were highly clonal, containi ng only females and displaying relatively low levels of genotypic dive rsity. Nevertheless, the distribution of genotypes within and among re gions was surprising. The bulk of sampled individuals (88 per cent) we re represented by just six common genotypes that were shared extensive ly among local populations and were geographically widespread. Individ ual samples contained a mean of 4.05, and up to 10, distinct four-locu s genotypes and overall we detected a total of 26 electrophoretically distinct genotypes. In combination, our results suggest that either th e south-eastern Australian populations of C. novaezelandiae arose thro ugh a recent colonization event (perhaps associated with an expansion of agricultural practices) or there is sufficient continuing gene flow between regions to prevent differentiation. However, the exact contri butions of sexual and asexual reproduction to dispersal in this ostrac od remain unclear.