The influence of androgenic steroid hormones on female aggression in ‘atypical’ mammals

Abstract

Dimorphism on dominance and agonistic behaviour in mammals tends to be strongly biased toward males. In this review, we focus on a select few species of mammals in which females are as or more aggressive than males, and/or are dominant to males, and explore the role of androgenic hormones in mediating this important difference. While the data are not as clear-cut as those published on traditional laboratory mammals, our review highlights important endocrine substrates for both organizational and activational influences of steroids on female aggressive behaviour. We highlight areas in which further observations and experiments are crucial, especially the potential facilitative effects of androgens on female aggression. Finally, new and innovative techniques, including molecular genetics and receptor pharmacology, portend important insights into the ways in which androgenic hormones regulate aggressive behaviour in 'atypical' female mammals.

Female competition and aggression: interdisciplinary perspectives

“…This suggests that T level alone is unlikely to fully explain sex differences in aggression. Interesting though, levels of the T precursor androstenedione (A 4 ) are more comparable between the sexes in certain female-dominant species, such as spotted hyenas (Crocuta crocuta) and ringtailed lemurs (Lemur catta) [84]. Studies of brain structure in adult spotted hyenas also reveal evidence of reduced sexual dimorphism in parts of the hypothalamus involved in mediating male-typical behaviour in mammals, hinting at neural substrates for enhanced female aggression [122].…”

“…In exceptional cases, adult females of certain species are consistently more aggressive than males [5,7,84]. More generally, females can occasionally be as aggressive as males (or more so) in competitive interactions [5,7,50,65,[84][85][86][87]. Hence an important goal is to determine how and why the competitive responses of the sexes are similar or different under various conditions, including competition for resources as well as mates.…”

“…Such diversity reveals that our understanding of the role of prenatal androgen exposure in mediating female aggression is still far from complete. In adulthood, female T levels are typically lower than males, even in species where females dominate males or are unusually aggressive ( [84]; see also Rosvall [121] and Campbell [102] this issue). This suggests that T level alone is unlikely to fully explain sex differences in aggression.…”

“…Although sexual selection theory offers a powerful explanation for sex differences in competitive behaviour [83], examples of intense female competition and aggression are not uncommon across a wide range of species with conventional sex roles [5 -7,13,36]. In exceptional cases, adult females of certain species are consistently more aggressive than males [5,7,84]. More generally, females can occasionally be as aggressive as males (or more so) in competitive interactions [5,7,50,65,[84][85][86][87].…”

“…French et al [84] explore hormonal mediators of female aggression among 'atypical' mammals in which females are more aggressive than and/or are dominant to males, including the role of androgenic steroids in both the developmental organization of neural structures underlying aggression [116], and the activation or facilitation of aggressive behaviour [117,118]. Both sexes produce testosterone (T) in the brain and gonads, possess androgen receptors in neural and peripheral tissues, and show behavioural and physiological responses to T [119].…”