Parasite-Driven Replacement Of A Sexual By A Closely Related Asexual Taxon In Nature

Abstract

Asexual species are thought to suffer more from coevolving parasites than related sexuals. Yet, this prediction may be modulated by the fact that closely related sexuals and asexuals often differ in respects other than reproductive mode. Here, we follow the frequency dynamics of sexual and asexual Daphnia pulex in a natural pond that was initially dominated by sexuals. However, coinciding with an epidemic of a microsporidian parasite infecting both sexuals and asexuals, the pond was rapidly taken over by the initially rare asexuals. We experimentally confirm that asexuals are less susceptible and also suffer less from the parasite once infected. These results show the ecological replacement of a sexual taxon by a closely related asexual taxon, as driven by parasites. We suggest that this replacement is, however, not directly connected with the reproductive mode, but rather due to the recent introduction and invasive nature of the asexuals studied.