Red Queen hypothesis supported by parasitism in sexual and clonal fish

THE Red Queen hypothesis for the maintenance of biparental sexual reproduction suggests that, for species locked in revolutionary struggles with biological enemies, the production of variable progeny compensates for the genetic or ecological disadvantages of sex1–7. The advantage of sex and recombination under this hypothesis stems from the production of rare phenotypes, which are expected to be more likely to escape infection or predation by coevolved biological enemies. Like many evolutionary hypotheses, the Red Queen hypothesis is difficult to test directly, but its assumptions and predictions can be evaluated7–18. The most critical assumption is that biological enemies will disproportionately attack the most common phenotype19, 20. In this study of parasite loads of coexisting sexual and clonal fish, we find empirical support for this assumption.