Sexual conflict and sexually transmitted infections (STIs): coevolution of sexually antagonistic host traits with an STI

In many taxa, there is a conflict between the sexes over mating rate. The outcome of sexually antagonistic coevolution depends on the costs of mating and natural selection against sexually antagonistic traits. A sexually transmitted infection (STI) changes the relative strength of these costs. We study the three-way evolutionary interaction among male persistence, female resistance, and STI virulence for two types of STIs: a viability-reducing STI and a reproduction-reducing STI. A viability-reducing STI escalates conflict between the sexes. This leads to increased STI virulence (i.e., full coevolution) if the costs of sexually antagonistic traits occur through viability but not through reproduction. In contrast, a reproduction-reducing STI de-escalates the sexual conflict, but STI virulence does not coevolve in response. We also investigated the establishment probability of STIs under different combinations of evolvability. Successful invasion by a viability-reducing STI becomes less likely if hosts (but not parasites) are evolvable, especially if only the female trait can evolve. A reproduction-reducing STI can almost always invade because it does not kill its host. We discuss how the evolution of host and parasite traits in a system with sexual conflict differs from a system with female mate choice.

在诸多分类群中，两性之间在交配速率方面存在冲突。性拮抗协同进化的结果取决于交配成本以及针对性拮抗性状的自然选择。性传播感染（sexually transmitted infection, STI）会改变这些成本的相对强度。本研究针对两类性传播感染——降低生存力型性传播感染与降低繁殖力型性传播感染，探讨雄性交配持续性、雌性交配抵抗性与STI毒力之间的三方进化互作关系。降低生存力型STI会加剧两性间的冲突。若性拮抗性状的成本源于生存力损耗而非繁殖力损耗，则该类STI会促使STI毒力上升（即完全协同进化）。与之相反，降低繁殖力型STI会缓解两性间的性冲突，但STI毒力并不会随之发生协同进化。本研究还探讨了不同进化能力组合下STI的定殖概率。若宿主（而非寄生虫）具备进化能力，尤其是仅雌性性状可进化时，降低生存力型STI成功入侵的概率会降低。而降低繁殖力型STI则几乎总能成功入侵，因其不会导致宿主死亡。本研究还讨论了存在性冲突的系统中，宿主与寄生虫性状的进化模式与存在雌性配偶选择的系统之间的差异。