How do self-fertilising and facultative sexual populations differ in mutation accumulation?

Abstract

AbstractSelf-fertilisation and asexual reproduction are both hypothesised to lead to long-term extinction due to inefficient selection acting against deleterious mutations. Self-fertilisation can counter these effects through creating homozygous genotypes and purging deleterious mutations. Although complete asexuality lacks meiotic gene exchange, mitotic gene conversion is a mechanism for creating homozygous regions that could limit deleterious mutation accumulation in a similar manner to self-fertilisation. Here, we compare mutation accumulation in self-fertilising and facultative sexual populations subject to mitotic gene conversion, to determine if the latter can purge deleterious mutations in an analogous manner to self-fertilisation. We first show analytically that this purging is most effective with high levels of asexuality and gene conversion, and when deleterious mutations are recessive. We further show using simulations that, when mitotic gene conversion becomes sufficiently high in obligate asexuals, there is a sudden reduction in the mutation count and a jump in homozygosity, reflecting mutation purging. However, this mechanism is not necessarily as efficient at purging compared to high levels of self-fertilisation, and elevated rates of mitotic gene conversion seem to be needed compared to empirical estimates. Hence, while mitotic gene conversion can remove recessive deleterious mutations, self-fertilisation seems to be a more effective mechanism for doing so.Teaser TextAsexuality has been argued to be an evolutionary ‘dead end’, due to a lack of gene exchange causing inefficient selection acting against deleterious mutations. It has been proposed that asexuals can counter these negative effects through mitotic gene conversion, which exposes mutations to selection within individual lineages. Here, we theoretically investigate how effective this mechanism is. We compare results to those obtained when individuals reproduce by self-fertilisation, which has similar effects on exposing deleterious variants. While mitotic gene conversion can be effective in removing recessive deleterious mutations, high rates are required and it is not always as effective as selfing.