Data from: Sperm competition risk drives rapid ejaculate adjustments mediated by seminal fluid

In many species, males can make rapid adjustments to ejaculate performance in response to sperm competition risk; however, the mechanisms behind these changes are not understood. Here, we manipulate male social status in an externally fertilising fish, chinook salmon (Oncorhynchus tshawytscha), and find that in less than 48 hr, males can upregulate sperm velocity when faced with an increased risk of sperm competition. Using a series of in vitro sperm manipulation and competition experiments, we show that rapid changes in sperm velocity are mediated by seminal fluid and the effect of seminal fluid on sperm velocity directly impacts paternity share and therefore reproductive success. These combined findings, completely consistent with sperm competition theory, provide unequivocal evidence that sperm competition risk drives plastic adjustment of ejaculate quality, that seminal fluid harbours the mechanism for the rapid adjustment of sperm velocity and that fitness benefits accrue to males from such adjustment.诸多物种的雄性个体均可针对精子竞争风险快速调整其射精表现，但此类调整背后的具体机制仍未阐明。本研究以体外受精鱼类奇努克鲑（Oncorhynchus tshawytscha）为研究对象，通过操控雄性的社会地位，发现当其面临升高的精子竞争风险时，雄性可在48小时内提升精子游动速度。通过一系列体外精子操控与竞争实验，我们证实精子游动速度的快速变化由精浆介导，且精浆对精子游动速度的调控作用会直接影响父权份额，进而影响繁殖成功率。本研究的综合发现与精子竞争理论完全契合，为此提供了确凿证据：精子竞争风险可驱动射精质量的可塑性调整，精浆蕴含了快速调控精子游动速度的机制，且雄性可通过此类调整获得适合度收益。