The coevolution of ova defensiveness with sperm competitiveness in house mice

Theoretical models have suggested that sperm competition can lead to increased ova resistance to fertilization. While there is some comparative evidence that this might be true, there is no experimental evidence to show that ova defensiveness evolves in response to sperm competition. We performed a series of in vitro fertilization assays to gauge the fertilizability of ova produced by female house mice from experimental populations that evolved either with or without sperm competition. Our analysis revealed that after 24 generations of experimental evolution, females that evolved under a polygamous regime produced more defensive ova than females that evolved under a monogamous regime. We therefore provide the first direct line of evidence that sperm competition can generate sexual conflict at the gametic level and lead to asymmetries in fertilization rates among populations. Our results show that females respond to sperm competition via fertilization barriers that have the potential to mediate sperm entry.

已有理论模型表明，精子竞争（sperm competition）可提升卵子（ova）对受精的抵抗能力。尽管已有部分比较研究证据支持这一假说，但尚无实验证据证实卵子的防御性会随精子竞争而演化。本研究开展了一系列体外受精（in vitro fertilization）实验测定，对来自经实验演化的小家鼠雌性个体所产生的卵子的受精能力进行了评估，这些实验种群分别在存在或不存在精子竞争的条件下完成演化。分析结果显示，经过24代实验演化后，处于多配偶制繁育体系下的雌性个体所产生的卵子，其防御性显著高于单配偶制繁育体系下的雌性个体。本研究首次提供了直接实验证据，证实精子竞争可在配子水平引发性冲突，并导致不同种群间受精率出现不对称性。研究结果表明，雌性个体可通过具备介导精子进入能力的受精屏障响应精子竞争。