Data from: Post-spawning sexual selection in red and white Chinook salmon (Oncorhynchus tshawytscha)

Post-copulatory processes, including sperm competition and cryptic female choice (CFC), can play important roles in the maintenance of polymorphisms. In Chinook salmon (Oncorhynchus tshawytscha), color morphs (red and white) exist due to genetic polymorphisms affecting carotenoid deposition in flesh, skin, and gametes. We investigated the role of post-spawning sexual selection in maintaining the polymorphism in a mixed population. First, we compared sperm velocity differences in water between morphs. Next, we measured color-based CFC via 2 methods: 1) sperm velocity in ovarian fluid and 2) in vitro competitive fertilization using paired red and white males. We found that red males had marginally faster sperm relative to white males in water, suggesting that carotenoid storage may affect sperm performance. However, ovarian fluid of red and white females influenced sperm velocity of red and white males differently, indicative of color-based CFC on sperm velocity. Furthermore, we found evidence of color-based CFC on paternity success during in vitro competitive fertilizations; however, sperm velocity in ovarian fluid did not predict results found under in vitro fertilization. Instead, in our study, sperm velocity in water was a significant predictor of fertilization success. When we accounted for this difference in sperm velocity (in water) between paired males, we partitioned the amount of variation in fertilization success that was attributed to individual level CFC (male pair × female) and male competitiveness (male pair) as 43% and 16%, respectively. In conclusion, post-spawning sexual selection processes represent important mechanisms contributing to the maintenance of the color polymorphism in nature.

交配后过程，包括精子竞争与隐蔽雌性选择（cryptic female choice, CFC），在多态性维持中发挥着关键作用。奇努克鲑鱼（Oncorhynchus tshawytscha）存在红色与白色两种体色形态，该性状由影响肌肉、皮肤及配子中类胡萝卜素沉积的遗传多态性所导致。本研究针对混合种群，探究了产卵后性选择在维持该体色多态性中的作用。首先，我们比较了不同体色雄性的精子在水体中的游动速度差异；随后，通过两种方法检测基于体色的隐蔽雌性选择：其一为卵巢液中的精子游动速度检测，其二为利用红色与白色雄性配对开展的体外竞争性受精实验。研究发现，在水体中红色雄性的精子游动速度略快于白色雄性，提示类胡萝卜素储存可能会影响精子功能。然而，红色与白色雌性的卵巢液对红色、白色雄性的精子游动速度的影响存在差异，表明存在基于体色的隐蔽雌性选择作用于精子游动速度。此外，我们在体外竞争性受精实验中发现了基于体色的隐蔽雌性选择影响父本成功率的证据，但卵巢液中的精子游动速度无法预测体外受精实验的结果；与之相反，本研究中水体中的精子游动速度是受精成功率的显著预测因子。当我们校正配对雄性间（水体中）的精子游动速度差异后，将受精成功率的变异来源拆解为个体水平的隐蔽雌性选择（雄性配对×雌性）与雄性竞争力（雄性配对），二者分别解释了43%与16%的变异。综上，产卵后的性选择过程是自然界中维持该体色多态性的重要机制。