57.5 Thursday, Jan. 5 Rapid evolution of sex frequency selected by requirement for dormancy and hydroperiod adaptation SMITH, H.A.*; SNELL, T.W.; Georgia Institute of Technology email@example.com
In many cyclical parthenogens that alternate between asexual and sexual reproduction, dormant stages produced by the sexual generation allow survival in ephemeral habitats. For example, in monogonont rotifers an asexual phase allows rapid population growth, whereas sex in these zooplankton results in resting eggs (diapausing embryos) capable of surviving desiccation. Few studies have experimentally tested whether sex-dormancy associations in temporary waters reflect evolution of sex in response to environmental conditions selecting for the diapausing stage, and whether evolution occurs via de novo mutations versus standing genetic variation and clonal replacement. Here we demonstrate higher sex propensity and diapausing embryo formation in ephemeral cultures mimicking temporary ponds, contrasted with permanent cultures. We report rapid evolution (in 385 d, ~80 generations) of lower sex propensity in permanent cultures, with data suggesting evolution occurred via new mutations. Mean sexual female frequency evolved to levels ~45% lower in permanent than ephemeral cultures, but asexual female density was twice as high—demonstrating a twofold cost of sex in cultures merely differing in sex frequency. Despite studies proposing occasional sex as a way to capture most of its benefits and minimize costs, cyclical parthenogens are shown to incur substantial costs from sex.