Data from: High temperatures reveal cryptic genetic variation in a polymorphic female sperm storage organ

Variation in female reproductive morphology may play a decisive role in reproductive isolation by affecting the relative fertilization success of alternative male phenotypes. Yet, knowledge of how environmental variation may influence the development of the female reproductive tract and thus alter the arena of post-copulatory sexual selection is limited. Yellow dung fly females possess either three or four sperm storage compartments, a polymorphism with documented influence on sperm precedence. We performed a quantitative genetics study including 12 populations reared at three developmental temperatures complemented by extensive field data to show that warm developmental temperatures increase the frequency of females with four compartments, revealing striking hidden genetic variation for the polymorphism. Systematic genetic differentiation in growth rate and spermathecal number along latitude, and phenotypic covariance between the traits across temperature treatments suggest that the genetic architecture underlying the polymorphism is shaped by selection on metabolic rate. Our findings illustrate how temperature can modulate the preconditions for sexual selection by differentially exposing novel variation in reproductive morphology. This implies that environmental change may substantially alter the dynamics of sexual selection. We further discuss how temperature-dependent developmental plasticity may have contributed to observed rapid evolutionary transitions in spermathecal morphology.

雌性生殖形态的变异可通过影响不同雄性表型的相对受精成功率，在生殖隔离过程中发挥决定性作用。然而，目前学界对于环境变异如何影响雌性生殖道发育，进而改变交配后性选择的作用场景的认知仍较为有限。黄粪蝇（Yellow dung fly）的雌性个体具有3个或4个精子储存室（sperm storage compartments），这一形态多态性已被证实会对精子竞争优先权产生显著影响。我们开展了一项定量遗传学研究，纳入了在3种发育温度下饲养的12个种群，并结合大量野外观测数据，结果显示：较高的发育温度会提升拥有4个储存室的雌性个体的频率，揭示了该多态性背后存在显著的隐匿遗传变异。沿纬度梯度呈现的生长速率与受精囊数量的系统性遗传分化，以及不同温度处理下各性状间的表型协变关系，提示该多态性的遗传架构由代谢速率相关的选择压力所塑造。本研究结果阐明了温度如何通过差异性暴露生殖形态的新型遗传变异，来调控性选择的前提条件。这意味着环境变化可能会大幅改变性选择的动态过程。我们还进一步探讨了温度依赖的发育可塑性，可能如何促成了已观测到的受精囊形态的快速进化转变。