Genetic diversity and polyploidy in the cosmopolitan asexual ostracod Cypris pubera

Abstract

Freshwater ostracods show extensive breeding system variation, but both the cause of breeding system transitions, and the origins of genotypic diversity in asexuals, have yet to be convincingly explained. The study reports on the genotypic (based on allozyme electrophoresis) characteristics of Northern European populations of the globally distributed ostracod Cypris pubera. No male has ever been described for C. pubera, and none were found in this study. Genotypic profiles indicated deviations from Hardy-Weinberg (HW) equilibrium, confirming that C. pubera reproduces through ameiotic parthenogenesis, that is, the production of female offspring where the formation of ova is through a mitotic process. Cypris pubera seems to be comprised of diploid clones that are brown in colour and a series of polyploid clones that are green. The two morphs often occurred in sympatry, but the green morph was considerably more diverse than the brown. The factors which contribute to asexual diversity or elevated ploidy levels in other taxa, such as hybridization, do not appear to be important for C. pubera. Thus, this study has established a link between polyploidy and genetic diversity in C. pubera, but the origins of both asexuality and polyploidy remain unclear for this ecologically successful ostracod.