Data from: Patterns of sperm swimming behaviour depend on male mating tactic and spawning environment in chinook salmon

Many species exhibit alternative mating tactics (ARTs), with larger, socially dominant males competing for females and smaller males adopting “sneaker” strategies to exploit fertilisation opportunities without competition or courtship. Females typically prefer larger socially dominant males, but their ability to manipulate mating or fertilisation outcomes is largely unknown. Here, using chinook salmon Oncorhynchus tshawytscha, we ask whether the female’s ovarian fluid (OF) differentially influences the temporal patterns of sperm swimming in ejaculates from non-preferred sneaker (‘parr’) and preferred (dominant) males. We demonstrate that OF improves sperm swimming speed and linearity compared to river water, regardless of male mating tactic, but also report a novel tactic-specific difference in sperm linearity; parr male sperm initially maintain straighter trajectories in river water, compared to dominant males, but then rapidly change to less linear and more circular paths over time. Intriguingly, we show that OF counteracts this change in sperm linearity in parr males so that patterns become indistinguishable from dominants when parr sperm swim in OF. Together, these results lead us to predict that male chinook salmon exhibit differential sperm trait investment strategies that depend on reproductive tactic.

诸多物种均存在替代性交配策略（Alternative Mating Tactics, ARTs）：体型更大、社会地位占优的雄性会通过竞争获取雌性，而体型更小的雄性则会采取"偷袭"策略，在不参与竞争或求偶的情况下伺机完成受精。雌性通常更青睐体型更大的社会优势雄性，但它们调控交配或受精结果的能力在很大程度上仍未被探明。本研究以奇努克鲑（Oncorhynchus tshawytscha）为实验对象，旨在探究雌性的卵巢液（Ovarian Fluid, OF）是否会对非偏好型偷袭雄性（‘parr’）与偏好型优势雄性的射精精子的游泳时序模式产生差异化影响。研究证实，无论雄性采用何种交配策略，相较于河水环境，卵巢液均可提升精子的游泳速度与运动直线性；同时我们还发现了一种全新的、与交配策略相关的精子直线性差异：与优势雄性的精子相比，偷袭型雄性（‘parr’）的精子在河水环境中初始轨迹更为笔直，但随着时间推移会迅速转变为直线性更低、圆周运动更多的轨迹。有趣的是，我们发现卵巢液能够抵消偷袭型雄性精子直线性的这种变化：当偷袭型雄性精子在卵巢液中运动时，其轨迹模式与优势雄性的精子已无显著差异。综合上述结果，我们推测奇努克鲑雄性会根据自身繁殖策略，采取差异化的精子性状投入策略。