Reproductive fluids enabling cryptic female choice of paternity do not induce concomitant ejaculate-mediated paternal effects in embryos of hybridizing salmonid fishes

Post-ejaculatory sexual selection in the form of cryptic female choice provides opportunities for females to bias paternity to favour preferred males. However, little is known regarding how cryptic female choice might affect offspring outside of paternity, via female-modified changes to environments that sperm experience prior to fertilization. Ejaculate-mediated paternal effects are widespread, and female alteration of sperm experience may play an unrecognized role in shaping cryptic female choice. Using hybridizing salmonid fishes that have documented female reproductive fluid-mediated conspecific sperm precedence, we created artificial split-brood and split-ejaculate fertilizations to determine if sperm experience in different fluids influences offspring development. Prior to contact with eggs, sperm experienced 20 s of swimming in either water, or water with the addition of conspecific female fluid or heterospecific female fluid. Over 186 days, we quantified hatch timing, hatchling size, and developmental stage and found that reproductive fluid from different species created biologically irrelevant (average effect size of 1.05%) changes on offspring development, which were much smaller than the effects of hybridization itself (average effect size of 10.44% for the species of the father). Since female reproductive fluid drastically changes fertilization conditions when compared to water, we conclude that females can use reproductive fluid to bias paternity without concomitant consequences to offspring development.