Ovarian fluid allows directional cryptic female choice despite external fertilization.

Suzanne H Alonzo,Susan E Marsh-Rollo,Kelly A Stiver

doi:10.1038/ncomms12452

Abstract

In species with internal fertilization, females can favour certain males over others, not only before mating but also within the female's reproductive tract after mating. Here, we ask whether such directional post-mating (that is, cryptic) female mate choice can also occur in species with external fertilization. Using an in vitro sperm competition experiment, we demonstrate that female ovarian fluid (ovarian fluid) changes the outcome of sperm competition by decreasing the importance of sperm number thereby increasing the relative importance of sperm velocity. We further show that ovarian fluid does not differentially affect sperm from alternative male phenotypes, but generally enhances sperm velocity, motility, straightness and chemoattraction. Under natural conditions, female ovarian fluid likely increases the paternity of the preferred parental male phenotype, as these males release fewer but faster sperm. These results imply females have greater control over fertilization and potential to exert selection on males in species with external fertilization than previously thought possible.

Highlights

In species with internal fertilization, females can favour certain males over others, before mating and within the female’s reproductive tract after mating
Our results show that females—through their ovarian fluid —can influence the nature and outcome of sperm competition among conspecific males, even in a species with external fertilization such as the ocellated wrasse (Symphodus ocellatus)
Our results provide evidence that female ovarian fluid changes the dynamics of fertilization at the gametic level and suggest a mechanism by which this might occur

Summary

Introduction

In species with internal fertilization, females can favour certain males over others, before mating and within the female’s reproductive tract after mating. Female ovarian fluid likely increases the paternity of the preferred parental male phenotype, as these males release fewer but faster sperm These results imply females have greater control over fertilization and potential to exert selection on males in species with external fertilization than previously thought possible. We ask whether female ovarian fluid provides a mechanism by which females can exhibit directional cryptic female mate choice— exerting directional sexual selection on adult male traits—even when fertilization happens outside of her body. To address this question, we performed a series of experiments that examine how female ovarian fluid affects the outcome of sperm competition and sperm characteristics in a species of fish with external fertilization and intense sperm competition. We consider if and how directional cryptic female mate choice affects selection on these alternative male phenotypes

Methods

Results

Conclusion