Genetic structure of cyclic parthenogenetic zooplankton populations - a conceptual framework

The genetic structure of cyclic parthenogenetic zooplankton populations is strongly determined by the consequences of combining sexual and asexual reproduction in the same life cycle. Since the pioneering population genetic studies on freshwater zooplankton in the 1970's, a distinction has been made between the genetic structure of permanent and intermittent populations. However, the results of many studies do not fit the expectations of this dichotomous model, for example when large lake populations are considered. In this paper, we present a unifying framework for understanding the genetic structure of cyclic parthenogenetic zooplankton populations, focusing on three factors that determine their degree of clonality and within-population genetic diversity as well as their among-population genetic differentiation: the size of the dormant egg bank, length of the growing season, and strength of clonal selection. We illustrate the importance of each of these factors, and show that our broader concept better explains the variation in genetic structure observed in natural populations of cyclic parthenogens than the earlier implicitly dichotomous model.