title: Sperm competition in humans: mate guarding behavior negatively correlates with ejaculate quality.
abstract: In species where females mate with multiple males, the sperm from these males must compete to fertilise available ova. Sexual selection from sperm competition is expected to favor opposing adaptations in males that function either in the avoidance of sperm competition (by guarding females from rival males) or in the engagement in sperm competition (by increased expenditure on the ejaculate). The extent to which males may adjust the relative use of these opposing tactics has been relatively neglected. Where males can successfully avoid sperm competition from rivals, one might expect a decrease in their expenditure on tactics for the engagement in sperm competition and vice versa. In this study, we examine the relationship between mate guarding and ejaculate quality using humans as an empirical model. We found that men who performed fewer mate guarding behaviors produced higher quality ejaculates, having a greater concentration of sperm, a higher percentage of motile sperm and sperm that swam faster and less erratically. These effects were found independent of lifestyle factors or factors related to male quality. Our findings suggest that male expenditure on mate guarding and on the ejaculate may represent alternative routes to paternity assurance in humans.
authors.affiliation: Centre for Evolutionary Biology & School of Animal Biology, University of Western Australia, Crawley, Australia; ARC Centre of Excellence in Cognition and its Disorders, School of Psychology, University of Western Australia, Crawley, Australia.
authors.forename: Samantha
authors.initials: S
authors.lastname: Leivers
authors.affiliation: ARC Centre of Excellence in Cognition and its Disorders, School of Psychology, University of Western Australia, Crawley, Australia.
authors.forename: Gillian
authors.initials: G
authors.lastname: Rhodes
authors.affiliation: Centre for Evolutionary Biology & School of Animal Biology, University of Western Australia, Crawley, Australia; ARC Centre of Excellence in Cognition and its Disorders, School of Psychology, University of Western Australia, Crawley, Australia.
authors.forename: Leigh W
authors.initials: LW
authors.lastname: Simmons
mesh_terms: D000328:Adult; D005260:Female; D006801:Humans; D008297:Male; D043762:Reproductive Behavior; D055101:Semen Analysis; D012725:Sexual Behavior; D012747:Sexual Partners; D013094:Spermatozoa / Q000166:cytology; D055815:Young Adult