Keeping deleterious mutations in check through sexual selection and inbreeding : an experimental approach in hermaphroditic snails

ELSA NOËL; ELISE FRUITET; NICOLÁS BONEL; PHILIPPE JARNE; PATRICE DAVID

Paris

Workshop; Simultaneously Hermaphroditic Organisms Workshop; 2018

Universidad de Paris 13

Theory and experiments have highlighted two processes that may facilitate the purge of the mutation load in genomes : inbreeding and sexual selection. Most of the literature on purge by inbreeding is on self-fertile hermaphrodites and most of the literature on purge by sexual selection is on gonochorists. Yet, we now have ample evidence that hermaphrodites can undergo intense sexual selection, so they have two ways to purge their genomes, and their relative importance determines the relative benefits of different mating systems. For example,when a hermaphrodite evolves from an outcrossing system towards predominant self-fertilization, purge by inbreeding starts while purge by sexual selection stops. It is therefore important to study and compare the efficiency of both mechanisms of genetic purge in hermaphrodites. We estimated the relative efficiency of inbreeding and sexual selection at limiting the accumulation of mutations, using lines of an outcrossing hermaphroditic snail (Physa acuta) that have undergone 60 generations of experimental evolution. Some lines experienced frequent self-fertilization, while others were outcrossing under different opportunities for selection on the male and female functions. Juvenile survival strongly decreased in outcrossing lines with reduced (sexual) selection on the male function, but not when selection was relaxed on the female function, showing the importance of sexual selection to keep deleterious mutations in check. However, lines with both reduced sexual selection and frequent selfing also showed high juvenile survival, suggesting that purging by inbreeding can compensate for the absence of sexual selection ? although not necessarily targeting the same types of mutations in the genome. Our results provide one of the most spectacular examples to date of the benefit of sexual selection, and suggest that inbreeding is, on the short term, an equally-efficient purging process. This points to the further question of whether a partially selfing strategy combining the advantages of both mechanisms could be optimal to keep a low mutation load in populations.