Guenther Scheffler

The Relationship of Cortisol Levels to Social Environment and Reproductive Functioning in Female Cotton-Top Tamarins, Saguinus oedipus

Cortisol levels were examined in 17 cotton-top tamarin monkeys (Saguinus oedipus) to determine: (1) if first-morning void urine sampling could be used as a noninvasive method for monitoring cortisol excretion, (2) if capture and bleeding were associated with changes in urinary cortisol levels, (3) the relative cortisol levels in reproductively active and reproductively suppressed females, and (4) the relationship between cortisol levels and changes in social condition in cotton-top tamarins. Mean urinary cortisol levels during ovarian cycling did not differ between captured and bled females and undisturbed females. Mean cortisol levels were significantly lower in females who were housed in their natal groups and reproductively suppressed than in the same females when they were removed and placed adjacent to a novel male and ovarian cycling began. For all females, mean cortisol levels were higher during the periovulatory period than during the nonperiovulatory period of the ovulatory cycle, with mean cortisol levels higher in newly cycling females than in long-term cycling females. No differences were found in mean cortisol levels between long-term cycling females and prepubertal females and postpubertal natal females. Cortisol levels from long-term cycling females were much lower than during the first two to three ovarian cycles occurring in newly cycling female tamarins, during the last part of pregnancy, and during the first 6 weeks postpartum. These data provide evidence that (1) suppression of ovarian cycling in postpubertal females remaining in their natal family is not associated with stress-induced changes in cortisol levels, (2) cortisol levels are not strictly tied to reproductive condition, and (3) social change may be reflected in cortisol elevation.

Social and reproductive influences on plasma cortisol in female marmoset monkeys

Subordinate female common marmosets (Callithrix jacchus) undergo ovulation suppression and exhibit low plasma cortisol levels compared to the dominant, breeding female. To determine whether this cortisol difference is mediated by the differential reproductive consequences of social status, we monitored plasma progesterone and cortisol in 32 adult female marmosets while they were housed in heterosexual pairs, during the first 3 days of heterosexual group formation, and while animals were housed in established social groups. Cortisol levels prior to group formation were significantly higher in females exhibiting cyclic ovulatory activity than in anovulatory females but were not predictive of social status. Subsequently, when animals were housed in established social groups, dominant (cyclic) females had significantly higher cortisol levels than did subordinate (anovulatory) females. Cortisol levels differed between the pre and postgroup formation conditions only in animals that underwent a corresponding onset or termination of ovulatory cyclicity. Cortisol differences between dominant and subordinate female marmosets therefore appear to be associated with differences in reproductive function rather than with social status per se.

Continued copulation in ovariectomized adrenal-suppressed stumptail macaques (Macaca arctoides)

Abstract Female stumptail macaques continue to copulate at moderate to high levels for years after gonadectomy. This study examined the extent to which sexual behavior of ovariectomized stumptail females was maintained by steroids of adrenal origin, and second, considered the possibility that ovarian fragments might have been left in situ following surgery. Daily injections of 0.1 mg of dexamethasone sodium phosphate suppressed serum cortisol, estradiol, and testosterone by at least 85% in three of four ovariectomized females, but dihydrotestosterone was suppressed by only 50 to 70%. The fourth female showed maximal suppression of cortisol but maintained much higher levels of the other steroids, in particular estradiol, and therefore it was strongly suspected that this animal had an ovarian fragment. Within the limits to which sex steroids were depressed with dexamethasone, no correlation was found between steroid levels and sexual performance. Ejaculatory frequencies and measures of attractivity, proceptivity, and receptivity collected during heterosexual pair tests remained unaffected in all four females during 4 weeks of dexamethasone treatment. Thus it was concluded that the maintenance of copulatory activity after ovariectomy in this species was largely due to nonsteroidal mechanisms.