Sperm competition accentuates selection on ejaculate attributes

Ejaculate attributes are important factors driving the probability of fertilizing eggs. When females mate with several males, competition between sperm to fertilize eggs should accentuate selection on ejaculate attributes. We tested this hypothesis in the North African houbara bustard (Chlamydotis undulata undulata) by comparing the strength of selection acting on two ejaculate attributes when sperm from single males or sperm from different males were used for insemination. In agreement with the prediction, we found that selection on ejaculate attributes was stronger when sperm of different males competed for egg fertilization. These findings provide the first direct comparison of the strength of selection acting on ejaculate attributes under competitive and non-competitive fertilizations, confirming that sperm competition is a major selective force driving the evolution of ejaculate characteristics.

精液性状（ejaculate attributes）是影响卵子受精概率的重要因素。当雌性与多只雄性交配时，精子间为争夺卵子受精机会而产生的竞争，会强化对精液性状的选择压力。我们以北非波斑鸨（Chlamydotis undulata undulata）为研究对象，通过对比使用单只雄性精子与多只雄性精子进行授精时，两种精液性状所受选择强度的差异，验证了这一假说。研究结果与预测一致：当不同雄性的精子竞争卵子受精机会时，精液性状所受的选择强度更高。本研究首次直接对比了竞争受精与非竞争受精情境下精液性状所受的选择强度，证实精子竞争是驱动精液性状演化的主要选择压力。