Data from: Evolution of female multiple mating: a quantitative model of the "sexually-selected sperm" hypothesis

Explaining the evolution and maintenance of polyandry remains a key challenge in evolutionary ecology. One appealing explanation is the sexually-selected sperm (SSS) hypothesis, which proposes that polyandry evolves due to indirect selection stemming from positive genetic covariance with male fertilization efficiency, and hence with a male’s success in post-copulatory competition for paternity. However, the SSS hypothesis relies on verbal analogy with ‘sexy-son’ models explaining co-evolution of female preferences for male displays, and explicit models that validate the basic SSS principle are surprisingly lacking. We developed analogous genetically-explicit individual-based models describing the SSS and ‘sexy-son’ processes. We show that the analogy between the two is only partly valid, such that the genetic correlation arising between polyandry and fertilization efficiency is generally smaller than that arising between preference and display, resulting in less reliable co-evolution. Importantly, indirect selection was too weak to cause polyandry to evolve in the presence of negative direct selection. Negatively-biased mutations on fertilization efficiency did not generally rescue runaway evolution of polyandry unless realized fertilization was highly skewed towards a single male, and co-evolution was even weaker given random mating-order effects on fertilization. Our models suggest that the SSS process is, on its own, unlikely to generally explain the evolution of polyandry.阐释一妻多夫制（polyandry）的演化与维持机制，始终是进化生态学领域的核心研究难题。其中颇具说服力的一种解释为性选择精子（sexually-selected sperm, SSS）假说，该假说提出，一妻多夫制的演化源于与雄性受精效率存在正向遗传协方差的间接选择，进而关联雄性在交配后父权竞争中的获胜成功率。然而，SSS假说仅依托于与"性感子代（sexy-son）"模型的文字类比——该模型用于阐释雌性对雄性展示性状的偏好的协同演化——而能够验证SSS核心原理的显性定量模型却极为匮乏。本研究构建了兼具类比性与遗传明确性的个体基模型（individual-based models），用以刻画SSS过程与"性感子代"过程。研究结果表明，二者间的类比仅部分成立：一妻多夫制与受精效率间产生的遗传相关度，通常低于雌性偏好与雄性展示性状间的遗传相关度，这导致协同演化的可靠性大幅降低。尤为关键的是，当存在负向直接选择时，间接选择的强度不足以驱动一妻多夫制发生演化。除非受精过程高度偏向单一雄性，否则针对受精效率的负偏突变通常无法挽救一妻多夫制的失控演化；若受精过程还受到随机交配顺序效应的影响，协同演化的程度甚至会进一步减弱。本研究模型表明，仅依靠SSS过程，通常难以全面阐释一妻多夫制的演化机制。