Data from: Feed-backs among inbreeding, inbreeding depression in sperm traits and sperm competition can drive evolution of costly polyandry

Ongoing ambitions are to understand the evolution of costly polyandry and its consequences for species ecology and evolution. Emerging patterns could stem from feed-back dynamics between the evolving mating system and its genetic environment, defined by interactions among kin including inbreeding. However, such feed-backs are rarely considered in non-selfing systems. We use a genetically-explicit model to demonstrate a mechanism by which inbreeding depression can select for polyandry to mitigate the negative consequences of mating with inbred males rather than avoiding inbreeding. Specifically, given inbreeding depression in sperm traits, costly polyandry evolved to ensure female fertility, without requiring explicit inbreeding avoidance. We show the mechanisms behind two main feed-backs. First, resulting sperm competition caused evolution of sperm traits and further mitigated the negative effect of inbreeding depression on female fertility. Second, the evolving mating system fed back to decrease population-wide homozygosity, and hence inbreeding. However, net overall reduction was small due to compound effects on the variances in sex-specific reproductive success and paternity skew. Purging of deleterious mutations did not eliminate inbreeding depression in sperm traits and hence selection for polyandry. Polyandry evolution, both directly and through sperm competition, might consequently facilitate evolutionary rescue for populations experiencing sudden increases in inbreeding.

本研究的核心目标在于解析代价高昂的一妻多夫制（polyandry）的演化历程，及其对物种种群生态与演化的影响。现有研究观测到的模式可能源自演化中的交配系统与其遗传环境之间的反馈动态——该遗传环境由包括近交（inbreeding）在内的亲属间相互作用所定义。然而，这类反馈动态在非自交体系中极少被纳入考量。本研究采用显式遗传模型（genetically-explicit model），揭示了一种机制：近交衰退（inbreeding depression）可正向选择一妻多夫制，以缓解与近交雄性交配带来的负面后果，而非通过主动规避近交达成该目标。具体而言，当精子性状存在近交衰退时，代价高昂的一妻多夫制会演化以保障雌性生育力，且无需显性的近交规避行为。本研究阐明了两类核心反馈背后的具体机制：其一，由此产生的精子竞争（sperm competition）会推动精子性状演化，并进一步缓解近交衰退对雌性生育力的负面影响；其二，演化中的交配系统会通过反馈效应降低种群整体的纯合性，进而减少近交发生。但由于性别特异性繁殖成功率变异与父权偏倚（paternity skew）的复合效应，整体的纯合性降幅极小。有害突变的清除并未消除精子性状的近交衰退，因此仍会维持对一妻多夫制的正向选择。综上，无论是直接作用还是通过精子竞争介导，一妻多夫制的演化或可帮助遭遇近交水平骤增的种群实现进化拯救（evolutionary rescue）。