Mating Competition, Promiscuity, and Life History Traits as Predictors of Sexually Transmitted Disease Risk in Primates

Competition among males influences the distribution of copulations and should therefore influence the spread of sexually transmitted diseases (STDs). We developed a model to investigate STDs in the mating and social systems found in primates, and we tested predictions using comparative methods. In the model, groups were distributed on a square lattice in which males or females disperse and males undergo characteristic dominance trajectories at maturity (challenge vs. queuing). We investigated the impact of mating rate, mating skew, migration rate of males or females, and group size on disease spread and prevalence. The model generated several predictions: 1) STD prevalence is higher in females than males; 2) STD risk increases with copulation rate; 3) high skew is negatively associated with STD risk; 4) STD risk is higher for all individuals when females disperse and 5) when mortality rates are lower; and 6) reproductive skew and later age of male dominance (queuing) produce more strongly female-biased STD prevalence. In comparative tests, we quantified STD risk as prevalence and richness of sexually transmitted organisms at the host species level. We found positive associations between host longevity and higher STD richness, and only (nonsignificant) weak trends for females to have higher STD prevalence. Mating skew showed a weakly positive association with STD richness, contrary to predictions of our model but consistent with predictions from a previous model. In some tests, we also found that female dispersal resulted in greater STD infection risk. Collectively, these results demonstrate that mating competition and demography influence patterns of STD infection, with mortality rates having the strongest effects in comparative tests.