Abstract
Sexual reproduction can facilitate adaptation of populations by reshuffling existing genetic variation or new mutations. However, sexual reproduction can also bear costs. Such costs come in two forms, direct costs and evolutionary costs. Direct costs are associated with the cost of producing males (twofold cost of sex) and the typically slower cell division during sexual reproduction. Evolutionary costs occur when too frequent sexual reproduction would hinder adaptation, by breaking apart adaptive allele combinations. Whereas the direct costs of sexual reproduction have been studied extensively, the evolutionary costs of sex remain less well understood. We investigate how the frequency of sexual reproduction affects adaptation to a non-stressful and a stressful environment in populations of the green alga Chlamydomonas reinhardtii, while minimizing the direct costs of sexual reproduction. Contrary to previous studies, we found that an increasing frequency of sexual reproduction hindered adaptation up to the point where adaptation was entirely prevented, suggesting strong evolutionary costs associated with too frequent sexual reproduction. This observation may explain the low frequency of sexual reproduction observed in many facultative sexual species.
Competing Interest Statement
The authors have declared no competing interest.