Cryptic female choice and gamete-mediated paternal effects in the context of interspecific hybridization

The environment in which fertilization takes place can have significant effects on paternity and offspring development. Through cryptic female choice, females can bias paternity to benefit a particular male and “choose” the father of her clutch. These processes might affect offspring development through non-genetic gamete-mediated paternal effects. I chose to examine the impact of cryptic female choice on paternity and offspring development in an externally fertilizing taxa that readily hybridizes, Salmoninae. Hybridization can represent a bad outcome for females with far-reaching effects on offspring phenotype and development. Females can reduce hybridization through conspecific sperm preference, a mechanism of cryptic female choice. What is unknown is the magnitude of conspecific sperm preference and the extent of gamete-mediated parental effects in our study populations and how these effects change in relation to hybridization. Following previous work done with other populations of salmonids, I expected to find evidence for strong conspecific sperm preference and paternal effects. Here, I examined conspecific sperm preference in three species, native brook char (Salvelinus fontinalis) and Atlantic salmon (Salmo salar), and introduced and invasive brown trout (Salmo trutta) and found that while ovarian fluid influenced sperm behavior, this effect did not differ among species. However, while hybridization between Atlantic salmon and brown trout significantly affected offspring development, paternal effects derived from the fertilization environment did not. This implies that females can alter paternity through cryptic female choice without consequences to the offspring. More research is needed in this and other salmonid species and populations to determine if these effects are present across salmonids

Can cryptic female choice prevent invasive hybridization in external fertilizing fish?

Abstract Polyandrous mating systems result in females mating with multiple males, generating opportunities for strong pre‐mating and post‐mating sexual selection. Polyandry also creates the potential for unintended matings and subsequent sperm competition with hybridizing species. Cryptic female choice allows females to bias paternity towards preferred males under sperm competition and may include conspecific sperm preference when under hybridization risk. The potential for hybridization becomes particularly important in context of invasive species that can novelly hybridize with natives, and by definition, have evolved allopatrically. We provide the first examination of conspecific sperm preference in a system of three species with the potential to hybridize: North American native Atlantic salmon (Salmo salar) and brook char (Salvelinus fontinalis), and invasive brown trout (Salmo trutta) from Europe. Using naturalized populations on the island of Newfoundland, we measured changes in sperm swimming performance, a known predictor of paternity, to determine the degree of modification in sperm swimming to female cues related to conspecific sperm preference. Compared to water alone, female ovarian fluid in general had a pronounced effect and changed sperm motility (by a mean of 53%) and swimming velocity (mean 30%), but not linearity (mean 6%). However, patterns in the degree of modification suggest there is no conspecific sperm preference in the North American populations. Furthermore, female cues from both native species tended to boost the sperm of invasive males more than their own. We conclude that cryptic female choice via ovarian fluid mediated sperm swimming modification is too weak in this system to prevent invasive hybridization and is likely insufficient to promote or maintain reproductive isolation between the native North American species