Ejaculate quality in spotted hyenas: intraspecific variation in relation to life-history traits

Abstract

Sperm competition has received much attention in recent years as a primary form of intrasexual competition among males, but little is known about variation in ejaculate quality in natural mammal populations, particularly among carnivores. Here, we documented variation in semen characteristics among wild male spotted hyenas (Crocuta crocuta). We then tested hypotheses suggesting that reproductive senescence among aging male hyenas is reflected in declining ejaculate quality, and that dispersal status affects ejaculate quality. To address these questions, we electroejaculated 20 wild males, including both immigrants and adult natal males. We found no support for the hypothesis that male spotted hyenas experience reproductive senescence with respect to their ejaculate quality, but we did find that immigrant males had significantly higher ejaculate quality than adult natal males, suggesting that adult natal males may experience reproductive suppression before dispersing. Finally, to test the assumption that an individual's ejaculate quality is consistent over time, we obtained repeated samples from 6 captive male hyenas. This captive work demonstrated significant individual repeatability in ejaculate quality and illustrated the utility of complementing field research with laboratory study. By exploring variation in ejaculate quality and its relationship with life-history traits in this unique species, we have highlighted new avenues for potential research regarding how sexual selection manifests in sex role—reversed species.