Androgens and aggressive behavior in primates: A review

Abstract

This review deals with possible central and peripheral effects of androgens upon primate aggressive behavior. One problem that clouds interpretation of experimental work is that measurements of dominance have often been employed, such as competition tests for food and water. Such measures often do not correlate with those obtained by quantifying aggressive interactions. It should be remembered that very few of the 188 primate species have been studied experimentally and that great behavioral and physiological diversity occurs within the order. Therefore, generalizations about the effects of androgens upon aggressive behavior in primates (including man) should be made with caution. Testosterone has an organizing influence upon the foetal brain of rhesus monkeys and may affect the development of neural mechanisms which govern aggression in males. More data are required on primates, however, since rhesus monkeys show some important differences from rodents as regards the effects of androgen upon sexual differentiation of the hypothalamus. In future, marmosets may provide a suitable model for such studies, because there is evidence that sexual differentiation of brain by androgen occurs postnatally in these monkeys. At puberty, male primates show a variety of behavioral changes and, during adulthood, males of seasonally breeding species may be more aggressive during the mating season, when testosterone levels are maximal. This does not indicate a causative relationship between testosterone and aggressive responses, because castration and androgen treatments have little effect upon aggression in prepubertal or adult males of several primate species. Androgens have pronounced effects on sexual responses in adult male monkeys, but their central effects upon aggression are much less important than among rodents. Elec trical stimulation of hypothalamic pathways has been employed to evoke aggressive behavior in marmosets and rhesus monkeys. In the rhesus, preliminary evidence indicates that such pathways show some sensitivity to androgens. In rodents it is known that these areas are richly supplied with monoaminergic neurons, which play an important role in aggressive behavior. There is little evidence on primates, however, and this remains a crucial topic for future research. Peripheral effects of androgens should also be considered. Many prosimians and New World monkeys use scent‐marking behaviors and, in males, androgen‐dependent chemical cues may be involved in sexual recognition and territorial behavior. This possibility awaits investigation. Finally, plasma testosterone levels may alter as a function of aggression itself; thus levels decrease if male rhesus monkeys are defeated by conspecifics. This might occur because neural events associated with giving (or receiving) aggression also influence pituitary function and hence alter gonadal testosterone secretion. Theoretically, it is possible that such changes in circulating testosterone might affect aggressive behavior via a feedback action on the brain, but ...

Testosterone and competitive ability in male house mice, Mus musculus: laboratory and field studies

“…Most studies conducted on this topic indicate that endocrine profiles change as a result of intermale interactions and that differences in circulating androgens prior to the interactions are not as important (Mazur 1976;Dixson 1980;Bernstein et al 1983). Running averages of androgen levels for males prior to and after realistic social contests are necessary to adequately test the hypothesis.…”

“…And finally, in hamsters, the size of the androgen-dependent flank gland is positively related to the position in a linear dominance hierarchy a male ultimately attains . The data are too few to conclude that aggression and dominance are mediated less by hormones in the more socially complex primates than in rodents, but this possibility has been suggested (Dixson 1980). The alternative to monitoring the fluctuating basal androgen levels in intact males is the kind of experiment we have presented here.…”

“…While testosterone appears to promote aggression, this behaviour does not necessarily facilitate dominance (e.g. Mazur 1976;Dixson 1980;Caldwell et al 1984;Sachser & Prove 1984;Berkovitch & Coy 1990). Moreover, dominance does not always guarantee high relative fitness; a myriad of other factors influence reproductive success.…”

Aspects of the behavioral and endocrine ontogeny of six moustached tamarins, <i>Saguinus mystax</i> (Callitrichinae)

“…The production of sex hormones such as testosterone increases during puberty until adult levels are reached (Plant, 1988). In adult males, testosterone and other androgens are important in the control of spermatogenesis (Wickings et al, 1986) and seem to play a role in the expression of aggressive behavior and in the achievement of social status, though this latter relationship might be less pronounced in primates (Dixson, 1980;Bouissou, 1983). In three callitrichine species (Callithrix jacchus, Callithrix kuhlii, and Saguinus oedipus), however, newborn males show relatively high testosterone levels that drop after two to six months and rise slowly again thereafter (Abbott, 1984;French and Schaffner, 1995;Ginther et al, 2002).…”

Androgens, progestagens and agonistic behaviour: A review

“…Sex hormones are related to both sexual and aggressive behaviour in a multifaceted way (10,22). Removal of gonads in males and females of several species produces changes in these behaviours in various ways.…”