When females mate promiscuously, sperm from rival males compete within the female reproductive tract to fertilize ova. Sperm competition is a powerful selective force that has shaped sexual behavior, sperm production, and sperm morphology. However, nothing is known about the influence of sperm competition on fertilization-related processes, because it has been assumed that sperm competition only involves a race to reach the site of fertilization. We compared four closely related rodent species with different levels of sperm competition to examine whether there are differences in the proportion of spermatozoa that become ready to interact with the ovum ("capacitated") and in the proportion of spermatozoa that experience the acrosome reaction in response to a natural stimulant. Our results show that differences between species in levels of sperm competition were associated with the proportion of spermatozoa that undergo capacitation and with the proportion of spermatozoa that respond to progesterone, an ovum-associated signal. Sperm competition thus favors a larger population of spermatozoa that are competent to fertilize, and spermatozoa that are more sensitive to the signals emitted by the ovum and that may penetrate the ova vestments more rapidly. These results suggest that, contrary to previous assumptions, competition between spermatozoa from rival males continues at the site of fertilization. These findings may have further evolutionary implications because the enhanced competitiveness of spermatozoa during fertilization may increase the risk of polyspermy to females. This could lead to antagonistic coevolution between the sexes and may contribute to the explanation of the rapid divergence observed in fertilization-related traits.

译文

:当雌性交配时,雄性对雄的精子在雌性生殖道内竞争,使卵子受精。精子竞争是一种强大的选择性力量,已经改变了性行为,精子产生和精子形态。但是,关于精子竞争对与受精有关的过程的影响一无所知,因为人们认为精子竞争仅涉及到到达受精位的竞赛。我们比较了具有不同精子竞争水平的四种密切相关的啮齿动物,以检查准备与卵子相互作用的精子的比例(“有能力的”)和经历顶体反应的精子的比例是否存在差异。天然的兴奋剂。我们的结果表明,不同物种之间精子竞争水平的差异与经历了获能的精子的比例以及对孕激素(与卵子相关的信号)作出反应的精子的比例有关。因此,精子竞争有利于有更多的受精能力的精子,而精子对卵子发出的信号更敏感并且可以更快地穿透卵巢。这些结果表明,与以前的假设相反,来自受敌雄性的精子之间的竞争在受精地点继续进行。这些发现可能具有进一步的进化意义,因为受精过程中精子竞争能力的增强可能会增加女性多精子的风险。这可能会导致两性之间的对抗性协同进化,并可能有助于解释受精相关性状中观察到的快速分歧。

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