Using individual-based modelling to investigate a pluralistic explanation for the prevalence of sexual reproduction in animal species

Attempts to resolve the paradox of sexual reproduction in animal species have typically involved single factor explanations, including but not limited to sexual species being better able to cope with fluctuating resources, being better able to evade pathogens and predators and sex facilitating the elimination of deleterious alleles. Only a handful of studies have investigated two potentially interacting factors, which most commonly involve the ability to evade pathogens and predators and mutation load; only two simulation studies by the same authors have examined the potential interaction of 3 factors.. Our study is the first three-factor study to examine the potential interaction between purifying selection, the ability to avoid predators and the ability to cope with fluctuating resources. Therefore, we addressed a number of open eco-evolutionary questions in our study: First, what is the effect of these three factors on the prevalence of sexual reproduction in animals? Second, do these factors act integratively, antagonistically or independently in determining the prevalence of sexual reproduction The ‘controls’ were our three prior studies where we investigated each of these factors individually. Our aim was to determine if the effect sizes in our individual studies were integratively enhanced by the interaction with the remaining two factors. What we found is that purifying selection purging deleterious alleles in sexual species was integratively enhanced by the two additional factors of increased predation and fluctuating resources. On the other hand, the effect of purifying selection and increased predation had an antagonistic effect on the levels of sexual reproduction and asexual reproduction in facultative species where there were fluctuating resources. Finally, the presence of an intermediate intensity deleterious allele and fluctuating resources had no discernable effect on the extinction levels of sexual and asexual species where there is increased predation. These results are not surprising, as there is no a priori reason to assume that multiple factors will have a greater impact on mode of reproduction than any of these factors acting independently. Our results suggest that multiple factors can act intergratively, antagonistically and non-reductively all at the same time, which is a significant contribution to the open question in the biological literature regarding the effect of multiple factors on the prevalence of sexual reproduction.