Genetic evidence of variation in the contributions of sexual and asexual reproduction to populations of the freshwater ostracod Candonocypris novaezelandiae

SUMMARY. 1 Genetic (electrophoretic) and sex ratio data were used to assess the contributions of sexual and asexual reproduction to recruitment to populations of the freshwater ostracod Candonocypris novaezelandiae in temporary and permanent water bodies of varying size.
2. Two distinct types of population structure were found. Populations from eight permanent ponds, a reservoir and a temporary pond, apparently comprised only females and were dominated by a few highly replicated genotypes. Significant departures from Hardy-Weinberg equilibria were observed for at least one locus in all populations, and multi-locus genotypic diversity ranged between 16% and 48% of that expected in a population with the same underlying gene frequencies reproducing solely by sexual means. These results were consistent with the predicted consequences of predominantly asexually derived recruitment.
3. In contrast, sexual reproduction was probably most important in a population inhabiting a large temporary swamp. This population displayed 79% of the genotypic diversity expected for a sexually reproducing population, and contained both males and females.
4. Most theoretical models predict that sexually reproducing individuals should have a selective advantage in unstable environments. The results of this study do not provide a perfect association of sexually derived recruitment with unstable habitats.