Female reproductive fluid and male seminal fluid: a non-gametic conflict for post-mating control.

Growing evidence shows that non-gametic components released by both males and females can significantly drive sperm competition outcomes. Seminal fluid (SF) was shown to influence paternity success by affecting rival males' sperm performance, and, in some species with male alternative reproductive tactics, to selectively decrease the fertilization success of males of the opposite tactic. Female reproductive fluid (FRF) has been proven to differentially influence ejaculates of different males and bias fertilization towards specific partners. Whether, and with what outcome, these two processes can intersect to influence sperm competition is still unknown. Here we explore this scenario in the grass goby (Zosterisessor ophiocephalus), a fish with territorial-sneaker reproductive tactics, where sneaker males can exploit the territorials' SF while penalizing territorial sperm performance with their own fluid. To test whether FRF can rebalance the ejaculate competition in favour of territorial males, we used in vitro fertilization with a SF mixture (territorial + sneaker), using increasing concentrations of FRF, to simulate the natural conditions that ejaculates encounter towards the eggs. Our findings revealed a differential effect of FRF on the different tactics' fertilization success, favouring territorial ejaculates, possibly through an attenuation of the detrimental effects of sneaker SF, and enabling females to regain control over the fertilization process.

Female reproductive fluid concentrations affect sperm performance of alternative male phenotypes in an external fertilizer.

There is growing evidence that the female reproductive fluid (FRF) plays an important role in cryptic female choice through its differential effect on the performance of sperm from different males. In a natural spawning event, the male(s) may release ejaculate closer or further away from the spawning female. If the relative spatial proximity of competing males reflects the female pre-mating preference towards those males, then favoured males will encounter higher concentrations of FRF than unpreferred males. Despite this being a common situation in many external fertilizers, whether different concentrations of FRF can differentially influence the sperm performance of distinct male phenotypes (favoured and unfavoured by the female) remains to be elucidated. Here, we tested this hypothesis using the grass goby (Zosterisessor ophiocephalus), a fish with distinct territorial-sneaker reproductive tactics and female pre-mating preference towards territorial males, that consequently mate in an advantaged position and whose sperm experience higher concentrations of FRF. Our findings revealed a differential concentration-dependent effect of FRF over sneaker and territorial sperm motility only at low concentrations (i.e. at the distance where sneakers typically ejaculate), with increasing FRF concentrations (i.e. close to the eggs) similarly boosting the sperm performance of both sneaker and territorial males. The ability to release sperm close to the eggs is a prerogative of territorials, but FRF can likewise advantage the sperm of those sneakers that are able to get closer, allowing flexibility in the direction of female post-mating choice.

Female Reproductive Fluid Increases the Opportunities for Postmating Sexual Selection by Prolonging the Egg Fertilization Window.

AbstractFemale reproductive fluid (the fluid that surrounds the eggs) has attracted increasing attention for its role in fertilization and postmating sexual selection through its effects on sperm traits. Surprisingly, however, only a few studies have investigated the effects of the female reproductive fluid on the eggs. Yet these effects might offer great potential to affect fertilization dynamics by, for example, increasing the opportunities for postmating sexual selection. Here, we determined whether the female reproductive fluid, by extending the egg fertilization window (the time available for egg fertilization), could also increase the opportunities for multiple paternity. Using the zebrafish (Danio rerio), we first tested the prediction that female reproductive fluid increases the egg fertilization window; then, using a split-brood design with the sperm of two males added at different time points after egg activation, we tested whether the degree of multiple paternity varies in the presence or absence of female reproductive fluid. Our results reveal the potential of female reproductive fluid to increase multiple paternity through its effects on the egg fertilization window, thus broadening our knowledge of how female mechanisms affect postmating sexual selection in externally fertilizing species.

Female comparative mate choice influences strategic male nesting strategy in the peacock blenny Salaria pavo.

Emerging evidence endorses the idea that comparative instead of rational choice is widespread among species and mating contexts. In a comparative scenario the attractiveness of a male is not absolute but depends on the attractiveness of the other males to whom he is compared by females. Therefore, a male may benefit from the ability to choose the appropriate context that enhances his attractiveness. Here we test for the occurrence of strategic male nesting strategies in the peacock blenny, Salaria pavo, a fish species in which females evaluate potential mates by comparing males. Our results show that the large majority of males choose the context that maximize their attractiveness by nesting close to less attractive neighbours. Overall, we suggest that, in the peacock blenny, comparative, non-directional female choice is associated to strategic male nesting strategies and this scenario may contribute to the maintenance of genetic variability of male sexually-selected traits.