Approximating the Coalescent Under Facultative Sex

Genome studies of facultative sexual species, which can either reproduce sexually or asexually, are providing insight into the evolutionary consequences of mixed reproductive modes. It is currently unclear to what extent the evolutionary history of facultative sexuals' genomes can be approximated by the standard coalescent, and if a coalescent effective population size N-e exists. Here, I determine if and when these approximations can be made. When sex is frequent (occurring at a frequency much greater than 1/N per reproduction per generation, for N the actual population size), the underlying genealogy can be approximated by the standard coalescent, with a coalescent N-e approximate to N. When sex is very rare (at frequency much lower than 1/N), approximations for the pairwise coalescent time can be obtained, which is strongly influenced by the frequencies of sex and mitotic gene conversion, rather than N. However, these terms do not translate into a coalescent N-e. These results are used to discuss the best sampling strategies for investigating the evolutionary history of facultative sexual species.

Automated summary

Genome studies of facultative sexual species provide insights into the evolutionary consequences of mixed reproductive modes. The approximation of the evolutionary history of facultative sexuals' genomes by the standard coalescent depends on the frequency of sexual reproduction. Sampling strategies for investigating the evolutionary history of facultative sexual species should take into account the frequency of sex and gene conversion rather than just the population size.