Data from: Coevolutionary feedbacks between female mating interval and male allocation to competing sperm traits can drive evolution of costly polyandry

Complex coevolutionary feedbacks between female mating interval and male sperm traits have been hypothesized to explain the evolution and persistence of costly polyandry. Such feedbacks could potentially arise because polyandry creates sperm competition and consequent selection on male allocation to sperm traits, while the emerging sperm traits could create female sperm limitation and, hence, impose selection for increased polyandry. However, the hypothesis that costly polyandry could coevolve with male sperm dynamics has not been tested. We built a genetically explicit individual-based model to simulate simultaneous evolution of female mating interval and male allocation to sperm number versus longevity, where these two sperm traits trade off. We show that evolution of competing sperm traits under polyandry can indeed cause female sperm limitation and, hence, promote further evolution and persistence of costly polyandry, particularly when sperm are costly relative to the degree of female sperm limitation. These feedbacks were stronger, and greater polyandry evolved, when postcopulatory competition for paternity followed a loaded rather than fair raffle and when sperm traits had realistically low heritability. We therefore demonstrate that the evolution of allocation to sperm traits driven by sperm competition can prevent males from overcoming female sperm limitation, thereby driving ongoing evolution of costly polyandry.

学界曾提出假说，认为雌性交配间隔与雄性精子性状之间的复杂协同进化反馈，可解释代价高昂的一妻多夫（polyandry）的演化与维持。这类反馈之所以可能存在，是因为一妻多夫会引发精子竞争（sperm competition），进而对雄性在精子性状上的资源分配产生选择压力；而新演化出的精子性状则可能造成雌性精子限制，由此进一步施加选择压力，推动雌性提高一妻多夫的程度。然而，关于代价高昂的一妻多夫可与雄性精子动态特征协同演化的假说，尚未得到实证检验。我们构建了一个遗传明确型基于个体的模型（genetically explicit individual-based model），用以模拟雌性交配间隔与雄性在精子数量和寿命间的资源分配的协同演化——这两种精子性状存在进化权衡（trade-off）。我们的研究结果显示，在一妻多夫情境下，参与竞争的精子性状的演化确实可引发雌性精子限制，进而推动代价高昂的一妻多夫的进一步演化与维持，尤其是当精子的生产成本相较于雌性精子限制的程度更高时。当交配后父权竞争采用加权抽奖（loaded raffle）而非公平抽奖模型，且精子性状的遗传力（heritability）处于符合实际的较低水平时，这类协同进化反馈会更强，且一妻多夫的演化程度也更高。因此，我们的研究证明，由精子竞争驱动的精子性状资源分配演化，会阻碍雄性克服雌性精子限制的过程，进而推动代价高昂的一妻多夫的持续演化。