Abstract
Harmful mutations are ubiquitous and inevitable, and the rate at which these mutations are removed from populations is a critical determinant of evolutionary fate. Closely related and otherwise similar sexual and asexual taxa provide a particularly powerful setting in which to study deleterious mutation elimination because sex should facilitate mutational clearance by reducing selective interference between sites. Here, we compared the rate of removal of conservative and radical nonsynonymous mutations in sexual vs. asexual populations of Potamopyrgus antipodarum, a New Zealand freshwater snail species featuring coexisting and ecologically similar sexual and asexual lineages. Our analyses revealed that radical changes are removed from populations at significantly higher rates than conservative changes and that sexual lineages eliminate these radical changes more rapidly than asexual counterparts, especially over relatively short time scales. Taken together, these results indicate that reduced efficacy of purifying selection in asexual lineages allows harmful mutations to remain polymorphic longer than in sexual lineages, potentially influencing the outcome of competition between sexual and asexual lineages. The fact that our ability to detect differential patterns of mutational clearance in sexual vs. asexual individuals required polymorphism data emphasizes the critical importance of population-level sampling for characterizing evolutionary phenomena.
