We’re interested in understanding the role that parasites play in the evolution of sex and mating strategies, and in turn, the role that host mating strategies play in the epidemiology and evolution of sexually transmitted infections. We’re also interested in the evolution of sex ratio.
Evolution of sex
- Parasitic castration promotes coevolutionary cycling which typically selects for sex, but also imposes an additional cost on sex in terms of finding a fertile mate, although this can be offset through multiple mating.
- Both population density and the type and strength of virulence are important for maintaining sex, which can be understood in terms of their effects on disease prevalence and severity. Even in the absence of heterozygote advantage, asexual heterozygosity affects coexistence with sex due to variation in niche overlap.
- Classical theory, which lacks eco-evolutionary feedbacks, predicts that the average fitness of sexual individuals will increase with the diversity of the population. However, we have shown that since high diversity suppresses disease prevalence this allows faster-growing asexual lineages to invade, so sex is most likely to persist at intermediate diversity (simulations below).
Parasite-mediated sexual selection
- Asymmetric (i.e. polygynous or polyandrous) mating systems affect the epidemiology and evolution of sexually transmitted infections through differences in information availability in males and females.
- Coevolution prevents the loss of mate choice that is predicted by non-coevolutionary theory and can lead to outcomes such as coevolutionary cycling in mate choice and STI virulence (simulations below). These dynamics are robust to a wide range of modelling assumptions.
- We have confirmed that the classical view of sex ratio evolution, popularised by R. A. Fisher (the sex ratio at birth should be equal when males and females require the same level of parental investment) is true, correcting recent modelling which appeared to contradict Fisher.
- While overall disease prevalence for sexually transmitted infections peaks at equal sex ratios, prevalence per sex peaks at skewed sex ratios. Furthermore, disease characteristics, sex-biased or not, drive predictable differences in male and female STI prevalence as sex ratio varies, with higher transmission and lower virulence generally increasing differences between the sexes for a given sex ratio.