Conflict and cooperation in a female-dominated society: A reassessment of the “hyperaggressive” image of spotted hyenas

Abstract

Summary It has been proposed that the evolution of female dominance in spotted hyenas (Crocuta crocuta) was due to selection for increased levels of androgens leading to increased aggressiveness and body size as well as to the development of an enlarged penile clitoris. Siblicide in spotted hyena twin litters has also been viewed as a by-product of selection for androgenized, aggressive adult females. These ideas, however, do not fit current knowledge of the behavior, ecology, and endocrinology of this species. We outline an alternative route to female dominance that links female control over mating (due to their enlarged clitoris) to the need for males to establish relationships with females before successful copulation is possible. This idea provides a likely explanation for habitual male submission to females, for low levels of aggression among competing males, for a lack of association between male social status and plasma androgen concentration, and for the investment by males in establishing relationships with females. Relationships with females improve with male tenure and are a nontransferable resource, and these are factors that are likely to have contributed to the evolution of a queue for social status among immigrant males. Free-ranging adult female spotted hyenas have perfectly ordinary, and thus not abnormally elevated, levels of androgens, and dominance in spotted hyena society is not related to body size. Hence, the assumed link between androgens, aggression, and body size does not exist. Aggression is not the only means of resolving conflicts among females, and there is substantial evidence that social relationships are a resource valued by females. As females that receive antiandrogen treatment during fetal development still develop an enlarged clitoris, androgen-dependent mechanisms are unlikely to be solely responsible for the development of this structure. Elevated levels of androgens in neonates of both sexes do not result in the “habitual” (obligate) death of a cub in same-sexed twin litters, and they are unlikely to result in contrasting behavior in adults (increased aggression in females, decreased aggression in males). Elevated levels of androgens in neonates are more likely linked to sibling rivalry and facultative siblicide when the milk provided by mothers falls below the level required to rear two cubs.