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.