A comparison of the behavior ofMacaca fascicularis andMacaca mulatta in relation to the menstrual cycle

Post-conception mating in wild long-tailed macaques (Macaca fascicularis): characterization, endocrine correlates and functional significance

In many anthropoid primates, mating activity is not restricted to the ovarian cycle but also occurs during pregnancy. Although it has been suggested that the main function of this post-conception mating is to confuse paternity, studies showing whether or not male primates can distinguish between the fertile phase of the conception cycle (FPCC) and the period of peak post-conception mating (peak PCM) are almost non-existent. Here, we examine whether the pattern of female sexual traits (specific sexual behaviors, sexual swelling) and female attractiveness to males differ between FPCC and peak PCM in 6 wild female long-tailed macaques. We also use fecal hormone analysis to investigate whether female traits during peak PCM are related to changes in female sex hormones. All females exhibited a distinct period of heightened mating activity around days 45-60 of gestation. During peak PCM, swelling size and frequency of female solicitations (but not reaching back) were significantly correlated with changes in the estrogen to progestogen ratio. Swelling size, frequency of female sexual behaviors and copulations and proportion of male-initiated copulations and ejaculations were not significantly different between FPCC and peak PCM. Although males spent significantly less time consorting females during peak PCM, all (particularly low-ranking and non-resident males) invested heavily in terms of reproductive costs associated with mate-guarding and mating during pregnancy. We conclude that post-conception mating in wild long-tailed macaques is not merely a by-product of endocrine changes and devoid of adaptive function. Our results more strongly support the hypothesis that it may form part of a female reproductive strategy to confuse paternity, which appears to apply particularly to low-ranking and extra-group males.

Female sexual behavior, but not sex skin swelling, reliably indicates the timing of the fertile phase in wild long-tailed macaques (Macaca fascicularis)

The extent to which catharrine primate males are able to discern the fertile phase during the female ovarian cycle under natural conditions is still debated. In a recent study, we showed that wild male long-tailed macaques are able to detect the fertile phase, but the cues males used to assess female reproductive status remained unclear. In the present study, we tested female sex skin swelling and specific female behaviors for their reliability in signaling the fertile phase, as determined by measurement of fecal estrogens (E) and progestogens (P) during nine ovulatory cycles in seven free-ranging females. We found that changes in sex skin swellings showed a significant positive correlation to the E/P ratio, but swelling size did not significantly differ between cycle phases. In contrast, the frequency of two of the tested female behaviors, namely initiation of sexual interactions and reaching back for the male during copulation, was not only correlated with female reproductive hormones, but was significantly elevated during the fertile phase compared to nonfertile phases of the cycle. We thus conclude that female sex skin swelling does not reliably indicate the timing of the fertile phase in long-tailed macaques, whereas certain female behaviors do. Since cycles differed considerably in the number of males with which females had sexual interactions as well as in the number of sexual interactions with dominant males, the signaling character of these specific female behaviors appears to be robust against inconsistencies in these social variables. Female behavior might therefore play an important role in the recognition of the fertile phase by male macaques under natural conditions.

Progesterone decreases mating and estradiol uptake in preoptic areas of male monkeys

Synthetic progestins such as medroxyprogesterone acetate (MPA) are used widely in the treatment of male sex offenders. In male cynomolgus monkeys (Macaca fascicularis) treated with testosterone (T), both MPA and progesterone (P) had comparable inhibitory effects on male sexual motivation and behavior. To determine if P, like MPA, decreases endogenous T levels, plasma T and P levels were analyzed in weekly blood samples (N=186) from eight intact males, each paired with a sexually receptive female before, during, and after treatment with subcutaneous Silastic P implants (336 behavior tests). P treatment decreased sexual activity but not plasma T levels. To ascertain if P, like MPA, acts by decreasing the nuclear uptake of T by brain, four P-treated and four control males were euthanized 60 min after intravenous injection of 3 mCi of [3H]T. The nuclear uptake of unchanged [3H]T and its metabolites [3H]E(2) and [3H]DHT was measured in samples of brain, pituitary gland, genital tract, and liver. P, unlike MPA, did not affect the nuclear uptake of [3H]androgens by brain, but reduced by 80% the nuclear accumulation of [3H]E(2) in tissue samples containing preoptic area and the anterior part of the bed nucleus of stria terminalis, although not in samples from hypothalamus or amygdala.

Effects of progesterone on the sexual behavior of castrated, testosterone-treated male cynomolgus monkeys (Macaca fascicularis)

In male cynomolgus monkeys the synthetic progestin, medroxyprogesterone acetate (MPA), decreases testosterone (T) levels and sexual behavior, binds to progestin receptors in brain, and reduces by about 70% the uptake of [3H]androgens by both brain and genital tract tissues. To examine the behavioral effects of progesterone (P) itself, eight castrated, T-treated males were each tested twice weekly with an estrogenized female before, during, and after they were treated with two SC Silastic P implants. Data from six 4-week treatment periods were analyzed to facilitate comparisons with our previous data using MPA: i) baseline, ii) weeks 4-7 of P treatment, iii) weeks 8-11 of P treatment, iv) weeks 1-4 after P implants were removed, v) weeks 5-8 after P withdrawal, and finally vi) weeks 9-12 after P withdrawal (384 1 h behavior tests). Weekly blood samples (N = 192) were analyzed by radioimmunoassay to determine plasma levels of both T and P. P treatment, which resulted in high plasma P levels (about 44 ng/ml), produced decrements in measures of male sexual behavior and motivation that were both qualitatively and quantitatively similar to those produced by MPA treatment but, unlike MPA, P did not decrease plasma T levels or change them in any way (about 850 ng/100 ml throughout). The findings suggest that P implants may be preferable to weekly MPA injections in the treatment of male sex offenders because they require less patient compliance and may not have MPA's troubling side effects.

Behavioral responses to Depo-Provera, Fadrozole, and estradiol in castrated, testosterone-treated cynomolgus monkeys (Macaca fascicularis): the involvement of progestin receptors

Sexual motivation and behavior decreased in male cynomolgus monkeys given either Depo-Provera (medroxyprogesterone acetate, MPA), which reduces androgen uptake by brain, or the nonsteroidal aromatase inhibitor, Fadrozole, which virtually eliminates the conversion of testosterone (T) to estradiol (E2) in brain. This suggested that both unchanged T and E2 are important for the control of male primate sexual behavior, but combined treatment with MPA and Fadrozole did not have the anticipated summatory effects in intact males: the behavioral decrements when MPA-treated males were given Fadrozole were about half those observed when Fadrozole was given alone. The present study tested the hypothesis that Fadrozole suppressed the behavioral effects of MPA by preventing the induction by E2 of progestin receptors in the brain to which MPA binds. Eight castrated, T-treated males were each tested with an estrogenized female i) during baseline, ii) during MPA treatment, iii) during treatment with MPA and Fadrozole together, and iv) with E2 treatment added to condition (iii) (256 1-h behavior tests). All dosages were those used in previous studies. Sexual motivation, as reflected in mounting attempts and mounting attempt latencies, was further diminished by E2 treatment in males receiving both MPA and Fadrozole, but ejaculatory activity was not changed. Immunocytochemistry demonstrated that the distributions of progestin and androgen receptors were little affected by MPA treatment, and that progestin receptor immunoreactivity was almost completely abolished in the brains of males receiving both MPA and Fadrozole but present in those receiving additional E2 treatment, findings that supported the hypothesis.

Combined effects of Depo-Provera and Fadrozole on the sexual behavior of intact male cynomolgus monkeys (Macaca fascicularis)

Our previous studies showed that treating castrated, testosterone-treated male cynomolgus monkeys with Depo-Provera (medroxyprogesterone acetate, MPA) decreased ejaculatory performance and also measures of male sexual motivation by about 40%. Similarly, treating castrated, testosterone-treated males with the nonsteroidal aromatase inhibitor, Fadrozole, decreased ejaculatory performance and male sexual motivation again by about 40%. These behavioral decrements are, of course, mediated by totally different mechanisms. We have therefore hypothesized that both unchanged T and E2 might be important for the control of sexual behavior in this male primate, and the present study examined the consequences of administering Fadrozole at a dose of 0.25 mg/kg/day to intact male cynomolgus monkeys being treated with 40 mg/week MPA. Intact males were each tested with an ovariectomized, E2-treated female partner (i) before treatment, (ii) during treatment with MPA alone, and (iii) during treatment with MPA and either Fadrozole or water administered SC by osmotic minipumps. As in previous studies, MPA significantly decreased plasma T levels and sexual behavior. But additional treatment with Fadrozole resulted in a rapid increase in plasma T levels although causing a further decline in sexual behavior. Results supported the view that both unchanged T and its aromatized product are important for ejaculatory activity and sexual motivation in the primate. Fadrozole's effect on plasma T may have been due to the elimination of the negative feedback of E2 on the hypothalamic-pituitary-gonadal axis.

Medroxyprogesterone acetate decreases the sexual activity of male cynomolgus monkeys (Macaca fascicularis): an action on the brain?

Medroxyprogesterone acetate (MPA), a synthetic progestin with androgen-depleting activity, is used to treat the deviant behavior of male sex offenders. In male cynomolgus monkeys, MPA reduces plasma testosterone (T) levels and sexual behavior, but the behavioral effects are clearly different from those of surgical castration. Because MPA is selectively taken up in unchanged form by the nuclei of neurons in the hypothalamus and preoptic area of male cynomolgus monkeys, and because it interferes with the uptake of T throughout the brain and pituitary gland, we have proposed that the behavioral effects of MPA may be mediated by brain mechanisms regulating sexual motivation that are relatively independent of circulating T levels. To test this hypothesis, eight castrated male cynomolgus monkeys bearing Silastic T implants SC were each observed during 60 min behavior tests with an ovariectomized, estrogen-treated female throughout three 4-week periods separated by 4-week periods without testing. After the first 4 weeks of testing, males received weekly IM injections of 40 mg MPA (six males) or vehicle (two males); the dose of MPA being equivalent on a body weight basis to those used clinically. Although plasma T was maintained in the upper range for intact males throughout the study, MPA treatment resulted in significantly decreased ejaculations and mounting attempts by weeks 5-6. These results demonstrated that the inhibitory effects of MPA on male behavior were independent of the reduction of plasma T levels, which points to a direct action on brain mechanisms controlling male sexual behavior.

A review of hormonal factors influencing the sexual and aggressive behavior of macaques

The effects of gonadal hormones on the sexual and aggressive behavior of adult macaques are reviewed. Similarities among findings from field, colony, and laboratory studies strengthen the view that testosterone facilitates the sexual and aggressive behavior of males, while sexual and perhaps aggressive behavior by the female is mainly dependent on estradiol, which increases both the sexual motivation of the female and her attractiveness to males. Differences between results from different settings help to emphasize the role of environmental and social factors in modulating the effects of hormones. © 1993 Wiley-Liss, Inc.

Medroxyprogesterone acetate and the nuclear uptake of testosterone and its metabolites by brain, pituitary gland and genital tract in male cynomolgus monkeys

The synthetic progestin, medroxyprogesterone acetate (MPA), is used to treat male sex offenders, and it is also suppresses sexual activity in male monkeys. To examine the possibility that MPA may act as an anti-androgen in the primate brain, 4 intact male cynomolgus monkeys were given MPA (40 mg i.m.) once a week for 16 weeks, while 4 control males received i.m. injections of vehicle. All males were then castrated and 3 days later were given 3 mCi [3H]testosterone ([3H]T) i.v.; 1 h after injection males were killed, and radioactivity in nuclear pellets obtained from the hypothalamus (HYP), preoptic area (POA), amygdala (AMG), septum, pituitary gland and genital tract was analyzed by HPLC. Concentrations of [3H]T and [3H]dihydrotestosterone in nuclear pellets were 65-96% lower in MPA-treated males than in controls (P less than 0.001), but the aromatized metabolite, [3H]estradiol, which was the major form of radioactivity present in nuclear pellets from HYP, POA and AMG, was unchanged. There were no differences in concentrations of [3H]T in supernatants from the tissues of MPA-treated and control males. Because the reduced nuclear uptake of androgen in brain occurred in males whose androgen-dependent behavior had been suppressed by MPA treatments, it is proposed that MPA may have anti-androgenic effects at the level of the cell nucleus in brain regions that control behavior.

Is the snark still a boojum? The comparative approach to reproductive behavior

One of Frank Beach's many achievements was his stimulating influence on the comparative study of behavior. This review honors that legacy by categorizing and describing the many kinds of comparative approaches in use today for the study of reproductive behavior. The categorization is based on the motives and goals of the researcher, the kinds of questions that can be answered, the number and phylogenetic relatedness of the species being compared, and the method used for analyzing the results. Each approach is illustrated with specific examples from recent research, using studies from the field of hormones and behavior whenever possible.

Effects of medroxyprogesterone acetate on plasma testosterone and sexual behavior in male cynomolgus monkeys (Macaca fascicularis)

Medroxyprogesterone acetate (MPA), a synthetic progestin with androgen-depleting activity, is used to treat the deviant sexual behavior of men. To investigate the effects of MPA in another anthropoid primate, 16 oppositely-sexed pairs of cynomolgus monkeys were observed in one-hour behavior tests during 15 successive 4-week periods conducted before, during and after administering to males weekly IM injections of first 20 mg and then 40 mg MPA. The doses used were comparable on a body weight basis to those employed clinically. Blood samples were collected weekly and assayed for plasma testosterone. During MPA treatment both plasma testosterone and ejaculatory behavior were significantly decreased, but the changes in behavior were less marked than the changes in hormone levels. There were clear differences between individual males in the effects of treatment, and the identity and hormonal status of the female partners also influenced the results. During the 6 month withdrawal period, effects were only partially reversible, and the data suggested that the behavioral changes depended on the hormonal changes rather than the opposite. However, a direct central action of MPA on behavioral mechanisms could not be excluded.

Testosterone and its metabolites in male cynomolgus monkeys (Macaca fascicularis): behavior and biochemistry

To extend our previous study on the behavioral effects of testosterone propionate (TP) and dihydrotestosterone propionate (DHTP) to a dose-range producing supra-physiological plasma androgen levels, 4 castrated cynomolgus monkeys were tested with the same 4 females during successive 4-week treatment periods while receiving 800 micrograms, 1.6 mg, 3.2 mg, 6.4 mg and 12.8 mg of TP or DHTP SC/day in counterbalanced order (16 pairs, 828 1-hr tests). Both androgens increased male sexual activity, but DHTP was less effective than TP in increasing the numbers of ejaculations per test and failed to restore ejaculations to intact levels. Giving androgen-treated males single injections of 50 micrograms and 100 micrograms estradiol benzoate (EB) was without any additional effect on behavior (16 pairs, 256 tests). To examine hormonal effects in the brain, castrated males were given either 3H-T or 3H-DHT, and tissues were examined by high performance liquid chromatography (hplc). After 3H-T, 3H-E2 and unchanged 3H-T were the major forms of radioactivity in nuclei from hypothalamus, preoptic area and amygdala. After 3H-DHT, unchanged 3H-DHT predominated. The lower behavioral effectiveness of DHT could not be ascribed to its failure to enter the brain. The data suggested a role for unchanged T in the regulation of ejaculatory behavior in a male primate.

Comparison of the effects of testosterone and dihydrotestosterone on the behavior of male cynomolgus monkeys (Macaca fascicularis)

To compare the behavioral effects of testosterone propionate (TP) and diyhdrotestosterone propionate (DHTP) at doses producing plasma levels of androgens within the physiological rage, observations were made on 4 castrated male cynomolgus monkeys during successive 4-week treatment periods while they received 25, 50, 100, 200, 400 and 800 micrograms of either TP or DHTP SC/day in counterbalanced order. Males were tested with each of the same 4 female partners (16 pairs, 1024 1-hr behavior tests). Males were injected at 1600 hr and blood samples were obtained at 0800 hr (256 samples, 456 hormone determinations). Physiological plasma levels of T resulted from the 200 micrograms and 400 micrograms TP treatments, and were associated with significantly increased ejaculatory behavior. Physiological plasma levels of DHT resulted from the 50 micrograms and 100 micrograms DHTP treatments, but there were no changes in ejaculatory behavior over the entire DHTP dose range used. This difference in the behavioral effects of TP and DHTP, not previously reported for a primate, could not be accounted for by the effects of treatment order, season, long-term behavioral testing, female sexual motivation or behavior reflecting the peripheral action of androgens.

Effects of testosterone on the behavior of male cynomolgus monkeys (Macaca fascicularis)

To determine the threshold doses of testosterone propionate (TP) that cause clear-cut behavioral changes in the sexual behavior of castrated male cynomolgus monkeys, observations were made on three males during successive 5-week treatment periods while they received daily subcutaneous doses of 100 micrograms TP increasing in octaves to 25.6 mg TP. Males were tested with each of the same two ovariectomized, estrogen-treated females (6 pairs, 330 1-hr behavior tests). To mimic the diurnal plasma testosterone rhythm, TP injections were given at 1600 hr and blood samples were obtained at 0800 hr (141 samples). Male ejaculatory activity increased at the threshold dose of 200 micrograms TP per day giving plasma testosterone levels of 830 ng/100 ml, which is in the physiological range of 600-1600 ng/100 ml for intact males. This threshold dose was eight times higher than in rhesus monkeys on a dose per kilogram body weight basis. There was a further marked increase in ejaculatory performance at higher doses (6.4 to 25.6 mg) giving supraphysiological plasma levels of 4000-9000 ng/100 ml. There were individual differences in the behavioral changes occurring with TP treatment, and the female partner modulated the effects. These findings were generally similar to those obtained with male rhesus monkeys, but certain species differences were noted.