ners (Coe et al., 1982), can rapidly suppress reproductive hormone secretion. However, not all psychological stresses have this effect. For example, exposing captive monkeys to the sight of “leather capture gloves” will lead to an increase in heart rate and cortisol, and a suppression of immune cell function, but will not suppress circulating levels of reproductive hormones (Helmreich and Cameron, 1992; Rogers et al., 1998). It seems likely that monkeys perceive the sight of capture gloves as being less threatening than a stress such as an aggressive attack by other monkeys. Thus, the perception of severity of stress is likely to be important in determining whether the stress will lead to a suppression of reproductive hormone secretion.
In nonhuman primates a number chronic social stresses have been associated with a marked and sustained suppression of reproductive hormone secretion. These include prolonged restraint stress (Goncharov et al., 1984) and troop reorganization (Sapolsky, 1983). Interestingly, in the Sapolsky study of baboon troop reorganization, several social factors appeared to modulate the response of the reproductive axis to stress in these animals. There was a high degree of correlation between aggressiveness and testosterone titers, with the more aggressive males showing higher circulating levels of testosterone. There was also an interaction between social status and the level of environmental stress, such that in periods of social stability there was no difference in plasma testosterone levels between dominant and subordinate animals, but in the period of social instability the dominant animals showed higher plasma testosterone levels than did the subordinate males. Similar findings were reported by Rose et al. (1972) in a study of male rhesus monkeys living together in a large outdoor compound, showing that plasma testosterone levels were correlated both with the number of aggressive interactions an animal experienced and the animal’s dominance rank. It has also been posited that social status (i.e., dominance rank) plays an important role in determining lifetime reproductive success in primates, with subordinate animals experiencing a greater degree of social stress and having a lesser degree of reproductive success (Cowlishaw and Dunbar, 1991; Dittus, 1979; Drickamer, 1974; Dunbar, 1980; Dunbar and Dunbar, 1977; Sade et al., 1976; Wilson et al., 1978). However, support for this hypothesis is not uniform, and this remains a controversial notion.
Some light may be shed on this issue by reports indicating a correlation between dominance rank and reproductive success in some years but not others (Cheney et al., 1988; deWaal, 1982; Duvall et al., 1976; Nishida, 1983; Witt et al., 1981). It would appear that multiple factors, including dominance rank, time of year, magnitude of stress, aggressiveness of the animal, and level of activity of the reproductive axis prior to stress exposure can all play roles in modulating the response of the reproductive axis to both acute and chronic stresses (see Figure 5-4). Thus, although it is pos-