Expression of adult female patterns of sexual behavior by male, female, and pseudohermaphroditic female rhesus monkeys

From pathology to pleasure: Reframing mechanistic studies on same-sex sexual behavior in primates

Same-sex sexual behaviors (SSB) in primates have historically been studied as sexual perversions, evolutionary paradoxes, and hormone-driven pathologies. Researchers in recent decades have challenged these perspectives, yet some of the original biases still linger. In this paper, we examine how the study of endocrinological mechanisms in SSB has been influenced by the historical framework of pathology. Societal attitudes and cultural conceptions of human sexuality have led researchers to study SSB in primates as the outcome of "abnormal" processes of "feminization" or "masculinization" of sexual behavior. Here, we argue for a renewed attention to other areas of inquiry regarding the relationship between hormones and SSB, such as the role of pleasure. We briefly review how current knowledge on the neuroendocrinology of pleasure in nonhuman primates may relate to the expression of SSB and highlight oxytocin and dopamine as potentially fruitful areas for future research. We argue that future studies on SSB in primates would benefit from 1) acknowledging how the historical study of SSB as a pathology has shaped mechanistic studies and 2) studying SSB with the same holistic approach as is taken with different-sex sexual behavior (DSB).

Prenatal Androgen Effects as a Proximate Mechanism Underpinning Variation in Social Behavior Among Female Nonhuman Primates

While the role of ecological factors in shaping primate social systems has been a central focus for decades, less attention has been given to phylogenetic relationships and the potential role of underlying proximate mechanisms. This study aimed to investigate the relationship between one such proximate mechanism, prenatal androgen effects (PAEs), and aspects of social behavior in female nonhuman primates using the 2D:4D ratio as a proxy for PAEs and phylogenetically controlled methods. In general, female 2D:4D ratios were highest in monogamous species (low inferred PAEs) and lowest in polygynandrous and polygynous species (high inferred PAEs). 2D:4D ratios also varied with the form of polygyny/polygynandry, potentially with regard to the need for competitive over cooperative behaviors and the intensity of female reproductive competition. Species characterized by female dominance had lower 2D:4D ratios than species characterized by male dominance or codominance. There were no significant relationships between 2D:4D ratio and either degree of frugivory or group size. Relationships between 2D:4D ratios and the directional consistency index and 2D:4D ratios and rates of female–female agonism were also nonsignificant although sample sizes for both of these variables were small. Female social relationships are a manifestation of complex competitive and cooperative behaviors and the results suggest that PAEs may act as a proximate mechanism underlying the expression of certain aspects of behavior in female primates in ways that are adaptive to their social system.

Naturally Occurring and Experimentally Induced Rhesus Macaque Models for Polycystic Ovary Syndrome: Translational Gateways to Clinical Application

Indian rhesus macaque nonhuman primate models for polycystic ovary syndrome (PCOS) implicate both female hyperandrogenism and developmental molecular origins as core components of PCOS etiopathogenesis. Establishing and exploiting macaque models for translational impact into the clinic, however, has required multi-year, integrated basic-clinical science collaborations. Paradigm shifting insight has accrued from such concerted investment, leading to novel mechanistic understanding of PCOS, including hyperandrogenic fetal and peripubertal origins, epigenetic programming, altered neural function, defective oocytes and embryos, adipogenic constraint enhancing progression to insulin resistance, pancreatic decompensation and type 2 diabetes, together with placental compromise, all contributing to transgenerational transmission of traits likely to manifest in adult PCOS phenotypes. Our recent demonstration of PCOS-related traits in naturally hyperandrogenic (High T) female macaques additionally creates opportunities to employ whole genome sequencing to enable exploration of gene variants within human PCOS candidate genes contributing to PCOS-related traits in macaque models. This review will therefore consider Indian macaque model contributions to various aspects of PCOS-related pathophysiology, as well as the benefits of using macaque models with compellingly close homologies to the human genome, phenotype, development and aging.

Androgens predict parasitism in female meerkats: a new perspective on a classic trade-off

The immunocompetence handicap hypothesis posits that androgens in males can be a 'double-edged sword', actively promoting reproductive success, while also negatively impacting health. Because there can be both substantial androgen concentrations in females and significant androgenic variation among them, particularly in species portraying female social dominance over males or intense female-female competition, androgens might also play a role in mediating female health and fitness. We examined this hypothesis in the meerkat (Suricata suricatta), a cooperatively breeding, social carnivoran characterized by aggressively mediated female social dominance and extreme rank-related reproductive skew. Dominant females also have greater androgen concentrations and harbour greater parasite loads than their subordinate counterparts, but the relationship between concurrent androgen concentrations and parasite burdens is unknown. We found that a female's faecal androgen concentrations reliably predicted her concurrent state of endoparasitism irrespective of her social status: parasite species richness and infection by Spirurida nematodes, Oxynema suricattae, Pseudandrya suricattae and coccidia were greater with greater androgen concentrations. Based on gastrointestinal parasite burdens, females appear to experience the same trade-off in the costs and benefits of raised androgens as do the males of many species. This trade-off presumably represents a health cost of sexual selection operating in females.

Effects of Long-Term Flutamide Treatment During Development on Sexual Behaviour and Hormone Responsiveness in Rams

Testosterone exposure during midgestation differentiates neural circuits controlling sex-specific behaviours and patterns of gonadotrophin secretion in male sheep. Testosterone acts through androgen receptors (AR) and/or after aromatisation to oestradiol and binding to oestrogen receptors. The present study assessed the role of AR activation in male sexual differentiation. We compared rams that were exposed to the AR antagonist flutamide (Flu) throughout the critical period (i.e. days 30-90 of gestation) to control rams and ewes that received no prenatal treatments. The external genitalia of all Flu rams were phenotypically female. Testes were positioned s.c. in the inguinal region of the abdomen, exhibited seasonally impaired androgen secretion and were azospermic. Flu rams displayed male-typical precopulatory and mounting behaviours but could not intromit or ejaculate because they lacked a penis. Flu rams exhibited greater mounting behaviour than control rams and, similar to controls, showed sexual partner preferences for oestrous ewes. Neither control, nor Flu rams responded to oestradiol treatments with displays of female-typical receptive behaviour or LH surge responses, whereas all control ewes responded as expected. The ovine sexually dimorphic nucleus in Flu rams was intermediate in volume between control rams and ewes and significantly different from both. These results indicate that prenatal anti-androgen exposure is not able to block male sexual differentiation in sheep and suggest that compensatory mechanisms intervene to maintain sufficient androgen stimulation during development.

Effects of prenatal androgens on rhesus monkeys: a model system to explore the organizational hypothesis in primates

After proposing the organizational hypothesis from research in prenatally androgenized guinea pigs (Phoenix, C.H., Goy, R.W., Gerall, A.A., Young, W.C., 1959. Organizational action of prenatally administered testosterone propionate on the tissues mediating mating behavior in the female guinea pig. Endocrinology 65, 369-382.), the same authors almost immediately extended the hypothesis to a nonhuman primate model, the rhesus monkey. Studies over the last 50 years have verified that prenatal androgens have permanent effects in rhesus monkeys on the neural circuits that underlie sexually dimorphic behaviors. These behaviors include both sexual and social behaviors, all of which are also influenced by social experience. Many juvenile behaviors such as play, mounting, and vocal behaviors are masculinized and/or defeminized, and aspects of adult sexual behavior are both masculinized (e.g. approaches, sex contacts, and mounts) and defeminized (e.g. sexual solicits). Different behavioral endpoints have different periods of maximal susceptibility to the organizing actions of prenatal androgens. Aromatization is not important, as both testosterone and dihydrotestosterone are equally effective in rhesus monkeys. Although the full story of the effects of prenatal androgens on sexual and social behaviors in the rhesus monkey has not yet completely unfolded, much progress has been made. Amazingly, a large number of the inferences drawn from the original 1959 study have proved applicable to this nonhuman primate model.

Elevated plasma testosterone concentrations during stallion-like sexual behavior in mares (Equus caballus)

Mounting interactions in mares isolated from stallions and the relationship to stage of the estrous cycle and level of circulating hormones were studied for 3 years in a herd averaging 105 mares. Mares were assigned to mounting, standing, and control groups. A control mare was selected by being within 1 day of the number of days after ovulation in a mounting mare. A total of 15 mounting interactions were detected by chance observation during the 3 years. A blood sample was collected immediately after the mounting interaction from each mare in the three groups, and a transrectal ultrasonographic examination of the reproductive tract was done. Two mounting interactions occurred during the early luteal phase and 13 during the follicular phase. The interactions that occurred during the follicular phase were used for comparisons among groups. The interval between mounting and the next ovulation, diameter of the two largest follicles, and the number of follicles larger and smaller than 20 mm were not different significantly among the mounting, standing, and control groups. Testosterone concentrations were higher (P<0.01) in the mounting group (17.7+/-2.3 pg/ml) than in standing group (10.9+/-0.5 pg/ml), and the difference between the mounting group and the control group (12.8+/-0.6 pg/ml) approached significance (P<0.08). Concentrations of androstenedione, estradiol, estrone, and progesterone did not differ significantly among groups. Results indicated that mounting behavior between mares is rare, usually occurs during the follicular phase, and is related to high circulating concentrations of testosterone.

Disruption of sexual function, FSH secretion, and spermiogenesis in rabbits following developmental exposure to vinclozolin, a fungicide

We studied sequelae of prenatal plus infantile exposure of male rabbits to vinclozolin, because it is ingested by women and children. Female Dutch-Belted rabbits (7–10/group) were treated daily per orum from gestation day 15 through post-natal week 4 to provide 0, 7.2, or 72 mg vinclozolin/kg dam’s body weight/day. Vinclozolin had no effect on maintenance of pregnancy, growth of pups, age at testicular descent or weight of organs. Concentrations of serum LH or testosterone at 6, 12, or 24 weeks of age were unaffected. However, FSH was lower (P< 0.05) in both vinclozolin groups at all three ages. Following injection of GnRH at 12 or 24 weeks, the increase in FSH was less (P< 0.05) in both vinclozolin groups, as was testosterone at 12 weeks of age. After full sexual maturity, 2 of 7 low dose rabbits were uninterested in female or male teasers and never achieved erection or ejaculation. Overall, rates of ejaculation failure were: control 0% (0/48), low dose 29% (12/42), and high dose 5% (3/60). Daily sperm production per gram of testis and total number of sperm per ejaculate in both vinclozolin groups were similar (P> 0.1) to controls. However, semen from vinclozolin rabbits contained over two times more (P< 0.05) morphologically abnormal spermatozoa, mostly nuclear and acrosomal defects, than semen from controls. Seminiferous tubules with degenerative changes were more frequent (P< 0.05) in vinclozolin rabbits than in controls. Lesions included syncytia of spherical spermatids and desquamation of germ cells. Hence, developmental exposure to vinclozolin caused presumably permanent changes in copulatory ability, secretion of FSH, and spermiogenesis.

Androgen excess fetal programming of female reproduction: a developmental aetiology for polycystic ovary syndrome?

The aetiology of polycystic ovary syndrome (PCOS) remains unknown. This familial syndrome is prevalent among reproductive-aged women and its inheritance indicates a dominant regulatory gene with incomplete penetrance. However, promising candidate genes have proven unreliable as markers for the PCOS phenotype. This lack of genetic linkage may represent both extreme heterogeneity of PCOS and difficulty in establishing a universally accepted PCOS diagnosis. Nevertheless, hyperandrogenism is one of the most consistently expressed PCOS traits. Animal models that mimic fetal androgen excess may thus provide unique insight into the origins of the PCOS syndrome. Many female mammals exposed to androgen excess in utero or during early post-natal life typically show masculinized and defeminized behaviour, ovulatory dysfunction and virilized genitalia, although behavioural and ovulatory dysfunction can coexist without virilized genitalia based upon the timing of androgen excess. One animal model shows particular relevance to PCOS: the prenatally androgenized female rhesus monkey. Females exposed to androgen excess early in gestation exhibit hyperandrogenism, oligomenorrhoea and enlarged, polyfollicular ovaries, in addition to LH hypersecretion, impaired embryo development, insulin resistance accompanying abdominal obesity, impaired insulin response to glucose and hyperlipidaemia. Female monkeys exposed to androgen excess late in gestation mimic these programmed changes, except for LH and insulin secretion defects. In utero androgen excess may thus variably perturb multiple organ system programming and thereby provide a single, fetal origin for a heterogeneous adult syndrome.

Two Cases of Spontaneous Pseudohermaphroditism in Cynomolgus Monkeys (Macaca fascicularis)

Disorders of genital development occur in all mammals. Hermaphroditism is a condition where the subject has genital organs of both sexes. True hermaphrodites have both ovarian and testicular tissue. Pseudohermaphrodites have only one type of gonadal tissue according to which they are classified as male or female pseudohermaphrodites. Two cases of spontaneously occurring pseudohermaphroditism in Cynomolgus monkeys (Macaca fascicularis) were seen here during 1999-2001. Both animals had female external genitalia, but each was found to have testicular tissue.

Sex differences in sexual partner acquisition, retention, and harassment during female homosexual consortships in Japanese macaques

Female Japanese macaques (Macaca fuscata) in certain populations are unusual in that they exhibit male-typical patterns of mounting behavior and sexual-partner preference. The goal of this study was to determine whether female Japanese macaques, from one such population, employ male-typical behavioral tactics to disrupt existing homosexual consortships, as well as to acquire and retain same-sex sexual partners. "Harassment" of homosexual consortships occurred when a sexually motivated, third-party male or female interrupted a consorting female couple by displacing or aggressing them. Sexual harassment was a male-typical strategy for disrupting existing homosexual consortships, but was rarely performed by females. "Intrusions" occurred when a male or female competitor attempted to acquire exclusive access to a female engaged in a homosexual consortship by targeting that female as the focus of competition and her partner as his/her competitor. "Sexual coercion" occurred when one individual alternately sexually solicited and aggressed another individual as part of the same behavioral sequence during an intrusion. Males employed consortship intrusions and sexual coercion when they attempted to acquire female sexual partners that were already engaged in homosexual consortships, but females rarely did so. However, females did employ male-typical patterns of aggressive competition and sexual coercion to retain same-sex sexual partners when confronted with male competitors' attempts to usurp those partners. These results indicate that female sexual activity during homosexual consortships is not uniformly "masculine" in expression, but rather is a mixture of male- and female-typical behaviors.

Sexual differentiation of sexual behaviour and preovulatory LH surge in ewes

Adult ewes were studied after prenatal treatment with androgen. Although seven of the eight androgenized ewes (ANDR) when intact presented signs of cyclic ovarian activity at least once, none of them showed cyclic female receptivity when intact or after ovariectomy and progesterone (P) + estradiol (E2) treatments, whereas all ten control (CONT) ewes did. Receptivity also was induced in CONT, but not in ANDR, ewes by long term E2 or testosterone (T) treatments. Increases in LH levels, with latency and duration similar to the LH surges of the CONT ewes, were observed in six (P + low E2 cycle) and five (P + high E2 cycle) of the eight ANDR ewes. The maximum LH level was lower in the ANDR than in the CONT ewes after high E2 treatment (p less than 0.002). Progesterone had a clear inhibitory effect on the induction of the LH surge by E2 only in the CONT ewes. Male-type mounting and nudging were observed more often in the ANDR than in the CONT ewes when intact (p less than 0.05). However, there was no facilitation of male sexual behaviour induced by long term E2 or T treatment in the ANDR compared to the CONT ewes. Progesterone inhibited male behaviour induced by T in the CONT but not in the ANDR ewes. This study shows that prenatal androgens defeminize LH secretion and sexual behaviour of ewes in a dissociated manner. It also suggests that prenatal androgen does not really masculinize the females but decreases their sensitivity to the inhibitory effect of P, and thus extends the "juvenile state" in which male-like patterns appear independently of the hormone milieu.

Copulatory behavior of adult tamarins (Saguinus fuscicollis) castrated as neonates or juveniles: effect of testosterone treatment

The sexual interactions of Saguinus fuscicollis males castrated as neonates, at 37 days of age, or prepubertally with adult intact females were studied. Prepubertally castrated males were observed while receiving testosterone, and while being treated with saline. Males castrated neonatally or at 37 days of age were observed while receiving testosterone. Neonatal castrates had previously been studied without hormone treatment and therefore no control condition was included for these animals. Prepubertally castrated males showed Mounts, Mounts with Thrusts, and Sexual Tongue Flicking when treated with saline only. In three of the four males, all measures of sexual behavior increased with testosterone treatment. Neonatally castrated males had failed to display any mounting or thrusting without testosterone treatment during a previous study. During the present study, three of the four males did not respond to testosterone treatment with sexual behavior. The fourth male and one male castrated at 37 days of age displayed some sexual behavior. These results suggest that most neonatally castrated males are not able to respond to testosterone with the activation of copulatory behavior. The findings are consistent with the hypothesis that in callitrichids the sensitive period for behavioral differentiation is shifted into neonatal life. However, some neonatally castrated males show a weak response to testosterone. This may reflect an extended and perhaps partially prenatal period of sensitivity.

Androgenic influences on body size and composition of adult rhesus monkeys

The effects of daily treatment with testosterone propionate (TP, 2 mg/kg) and dihydrotestosterone propionate (DHTP, 2 mg/kg) were examined in rhesus monkeys in three experiments. In experiments 1 and 2, males and females gonadectomized in infancy, and female pseudohermaphrodites produced by prenatal exposure to TP or DHTP and gonadectomized postpubertally, were studied in conjunction with intact males (IM). The IM group was heavier in adulthood than the three gonadectomized groups, which did not differ in body weight from each other. Genetic males had greater crown-rump length than genetic females. Treatment of the gonadectomized groups with TP produced large increases in body mass (averaging approximately 50%) that were attributable to accretion of lean tissue. This effect did not differ significantly between males and females. In experiment 3, additional groups of males that had been castrated as infants were given daily injections with DHTP or oil. The DHTP treatment resulted in increases in body size that were not different from those seen following TP treatment. When TP and DHPT treatments were discontinued, body weights and dimensions reverted to base-line values. Increased body size induced by TP and DHTP was accomplished without reliable increases in food intake. Because testosterone (T) is metabolized to dihydrotestosterone (DHT), while DHT cannot be converted to T, these results show that both T and DHT are effective anabolic hormones in rhesus.

Analysis of sex and regional differences in androgen receptors in fetal rhesus monkey brain

Cytosolic androgen receptor levels were measured in different brain regions of fetal male and female rhesus monkeys (day 135 post-conception). The hypothalamus-preoptic area, amygdala and cerebellum exhibited higher receptor concentration in comparison to the cerebral cortex (parietal, temporal frontal, and occipital lobes), hippocampus and cingulate gyrus (P less than 0.001). No sexual difference in receptor concentrations was found except in the amygdala where fetal males exhibited slightly higher levels than females. The similarity in androgen receptor levels suggests that the developing brain of both sexes could be influenced by circulating androgens under normal or pathological conditions.

Expression of male-typical behavior in adult female pseudohermaphroditic rhesus: comparisons with normal males and neonatally gonadectomized males and females

Two types of pseudohermaphroditic female rhesus produced by exposure to either testosterone propionate (TP) or dihydrotestosterone propionate (DHTP) prior to birth were ovariectomized postpuberally and evaluated for the display of male-typical sexual behavior in response to exogenous TP in adulthood (2 mg/kg/day for 12 weeks). Their performance in standardized tests with estrogenized female partners was compared to that of neonatally gonadectomized males and females identically tested and treated with exogenous TP as adults. In addition intact adult males not given exogenous TP were tested with the same estrogenized female partners. There were no reliable differences between the two types of pseudohermaphrodites on any measure of behavior shown during the tests. Accordingly results were combined. Reliable behavioral changes induced by the TP given in adulthood were limited to increases in purse-lip responses, the induced increases were similar in pseudohermaphrodites and castrated males, and increases were reliably greater in these two groups of subjects than in females. Pseudohermaphrodites and castrated males did not differ reliably from intact males in performance of purse-lip gestures during TP treatment. In the performance of mounting, however, pseudohermaphrodites and castrated males remained consistently below the standard of the intact males. The estrogenized female partners displayed proceptive responses most frequently to the intact males and least frequently to the females. Their proceptive responses with castrated males resembled their performance with intact males, but with pseudohermaphrodites their proceptive responses more closely resembled their performance with females. Receptive behavior of the female partners was displayed most frequently to intact males, at intermediate levels to castrated males, and least often to pseudohermaphrodites. Results are completely consistent with the notion that androgens in high concentrations before birth alter mechanisms related to the later display of masculine behavior. These alterations in behavioral mechanisms are of such a nature that the display of male-typical behavior induced by androgens in adulthood is more pronounced and more frequent than it would have been otherwise. The alterations in masculine behavior observed in pseudohermaphroditic rhesus are not different in kind or scope than those reported extensively for lower mammals.(ABSTRACT TRUNCATED AT 400 WORDS)

Female-typical sexual behavior of rhesus and defeminization by androgens given prenatally

Adult rhesus monkeys were observed in standardized tests for female-typical sexual and related social responses. In the first experiment reported, 7 castrated males and 5 spayed females were paired with each of 4 intact males on two occasions following intramuscular injection with estradiol benzoate (EB) (6 micrograms/kg X 14 days) and on two other occasions without such treatment. In tests without EB, males and females did not behave differently toward the intact male partners, and all responses were displayed at low frequencies. In tests with EB, females showed reliably higher frequencies than males of approaching, sitting close to, grooming, and soliciting, and they presented to a higher proportion of the male partner's sexual contacts. EB reliably increased the frequency of display of all of these same five responses in females but not in castrated males. The intact male partners displayed reliably fewer approaches, sexual contacts, mounts, intromissions, and ejaculations to castrated males than to spayed females regardless of estrogenization. In a second experiment 10 intact adult pseudohermaphroditic females and 6 intact control females were tested following EB injections with each of the same 4 intact males. Pseudohermaphrodites were experimentally produced by injecting pregnant females with either testosterone propionate (TP) or dihydrotestosterone propionate (DHTP). Pseudohermaphrodites, regardless of type of androgen used in their production, showed reliably fewer solicits than controls to male partners. Moreover, they displayed most of the other responses at lower average frequencies than controls. Frequencies of intromission and ejaculation by intact male partners were reliably lower with pseudohermaphrodites than with control females, but frequencies of approach, sexual contact, and mount were not reliably different. We conclude that in this testing and measurement situation male and female rhesus monkeys differ markedly in the degree of expression of female-typical sexual behaviors, and genotypic males are behaviorally less responsive to estrogens than females. Exposing genotypic females to androgens during fetal life decreases the expression of female-typical, estrogen-influenced responses, and the effect is most pronounced on those soliciting responses that subserve proceptivity.