Ovarian fluid allows directional cryptic female choice despite external fertilization.

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.

81 citations (Crossref) [2023-10-31] Place: England Alonzo, Suzanne H. Department of Ecology and Evolutionary Biology, Yale University, 165 Prospect Street, New Haven, Connecticut 06520, USA. Alonzo, Suzanne H. Department of Ecology and Evolutionary Biology, University of California Santa Cruz, 1156 High Street, Santa Cruz, California 95064, USA. Stiver, Kelly A. Department of Ecology and Evolutionary Biology, Yale University, 165 Prospect Street, New Haven, Connecticut 06520, USA. Stiver, Kelly A. Psychology Department, Southern Connecticut State University, 501 Crescent Street, New Haven, Connecticut 06515, USA. Marsh-Rollo, Susan E. Department of Ecology and Evolutionary Biology, University of California Santa Cruz, 1156 High Street, Santa Cruz, California 95064, USA. Marsh-Rollo, Susan E. Department of Psychology, Neuroscience, and Behaviour, McMaster University, 1280 Main Street W, Hamilton, Ontario, Canada L8S4K1.