Reproductive skew among males in a female-dominated mammalian society

The purpose of this study was to document patterns of reproductive skew among male spotted hyenas (Crocuta crocuta), a species in which many normal mammalian sex roles are reversed. We used paternity determined from 12 microsatellite markers together with demographic and behavioral data collected over 10 years from a free-Thing population to document relationships among reproductive success (RS), social rank, and dispersal status of male hyenas. Our data suggest that dispersal status and length of residence are the strongest determinants of RS. Natal males comprise over 20% of the adult male population, yet they sire only 3% of cubs, whereas immigrants sire 97%. This reproductive advantage to immigrants accrues despite the fact that immigrants are socially subordinate to all adult natal males, and it provides a compelling ultimate explanation for primary dispersal in this species. High-ranking immigrants do not monopolize reproduction, and tenure accounts for more of the variance in male reproductive success than does social rank. Immigrant male hyenas rarely fight among themselves, so combat between rivals may be a relatively ineffectual mode of sexual selection in this species. Instead, female choice of mates appears to play an important role in determining patterns of paternity in Crocuta. Our data support a limited control model of reproductive skew in this species, in which female choice may play a more important role in limiting control by dominant males than do power struggles among males.