Using individual-based modelling to investigate the possible role that the Red Tooth effect plays in maintaining sexual reproduction

One possible explanation for the prevalence of sexual reproduction in animal species is that in the context of predator-prey dynamics, sexually reproducing prey are better able to evade predators than their asexual counterparts. This is known as the Red Tooth hypothesis, a term coined by French (2010). It is a special case of the more generic Red Queen hypothesis, which explains the prevalence of sex not only in terms of advantages to prey but also in terms of advantages to hosts in the face of pathogens, based on the assumption that pathogen-host and predator-prey dynamics are analogous. In this study, we test the Red Tooth hypothesis using individual-based computer modeling simulations, where additional predators are introduced during the simulation process for sexual, asexual and facultative species. Our results indicate that after the introduction of increased predation, sexual species have significantly higher escape ratios vs. their asexual counterparts, explainable by the higher energy levels of sexual prey vs. asexual prey. However, there is a significant decrease in population levels of sexual prey vs. asexual prey. This lower population level of sexual prey may be explainable by the fact that sexual and asexual prey evolve different strategies in response to increased predation: Whereas sexual prey evolve higher energy levels and hence greater body size with a higher ratio of escape behaviors requiring more food which limits population size, asexual prey remain smaller requiring less food and with a lower ratio of escape behaviors but with an increased ratio of successful reproductive attempts resulting in larger populations. An additional factor in lower population levels of sexual prey is a higher kill ratio possibly due to vulnerability related to mating. Moreover, we found that in experimental runs, the species extinction ratio was noticeably lower for sexual vs. asexual prey after the 15,000th time step following increased predation, albeit below the threshold of statistical significance. Our results show that sexual reproduction may be selected in predator-prey systems given the lower rate of species extinction in support of the Red Tooth hypothesis