Within-population sperm competition intensity does not predict asymmetry in conpopulation sperm precedence

Postcopulatory sexual selection can generate evolutionary arms races between the sexes resulting in the rapid coevolution of reproductive phenotypes. As traits affecting fertilization success diverge between populations, postmating prezygotic (PMPZ) barriers to gene flow may evolve. Conspecific sperm precedence is a form of PMPZ isolation thought to evolve early during speciation yet has mostly been studied between species. Here , we show conpopulation sperm precedence (CpSP) between Drosophila montana populations. Using Pool-seq genomic data we estimate divergence times and ask whether PMPZ isolation evolved in the face of gene flow. We find models incorporating gene flow fit the data best indicating populations experienced considerable gene flow during divergence. We find CpSP is asymmetric and mirrors asymmetry in non-competitive PMPZ isolation, suggesting these phenomena have a shared mechanism. However, we show asymmetry ...交配后性选择（Postcopulatory sexual selection）可引发两性间的进化军备竞赛（evolutionary arms races），进而推动生殖表型（reproductive phenotypes）快速协同演化。当影响受精成功率的性状在不同种群间发生分化时，交配后合子前（postmating prezygotic, PMPZ）基因流阻隔便可能随之演化形成。同种精子优先（conspecific sperm precedence）是一种被认为会在物种形成（speciation）早期演化出现的PMPZ生殖隔离形式，但目前相关研究大多聚焦于物种间的该类隔离机制。本研究中，我们在山果蝇（Drosophila montana）种群间证实了同种群精子优先（conpopulation sperm precedence, CpSP）现象。借助混池测序（Pool-seq）获得的基因组数据，我们估算了种群分化时间，并探究了PMPZ生殖隔离是否在存在基因流（gene flow）的背景下发生演化。研究结果显示，纳入基因流因素的模型对数据拟合度最优，表明种群在分化过程中曾经历显著的基因交流。我们发现CpSP现象存在不对称性，且与非竞争性PMPZ生殖隔离（non-competitive PMPZ isolation）的不对称性特征相呼应，提示二者共享同一套演化机制。然而，我们证实不对称性……