Effect of ovariectomy at two periods of the year on LH and FSH basal concentrations and pituitary response to LHRH in the brown hare (Lepus europaeus)

In the brown hare, fertile mating takes place from the beginning of December to September. Seasonal variations of basal concentrations of LH and FSH, and pituitary response to a monthly i.v. injection of LHRH were studied in intact control females and in females ovariectomized during the seasonal anoestrus (OVX1) or during the breeding season (OVX2). In intact females, both basal and LHRH-stimulated LH levels showed an annual variation, with minimal values during anoestrus. During the breeding season, the LH response to LHRH exhibited a biphasic pattern. In contrast, there was no clear seasonal variation in basal and LHRH-stimulated FSH concentrations. After ovariectomy during anoestrus, basal LH remained low for 2 months and began to increase in December. After ovariectomy during the breeding season, LH basal concentrations increased within a few days after the operation. Thereafter, LH values remained high in both groups of females until September, and decreased significantly as in intact females. The pattern of LH release after LHRH remained monophasic in the two groups of ovariectomized females. In OVX1 females, the LH response increased as early as October, was maximum from December to April and decreased progressively until October. IN OVX2 females, the LH response decreased regularly after ovariectomy to a minimum in October. In the 2 groups of ovariectomized females, basal FSH concentrations and pituitary response to LHRH rose rapidly after ovariectomy and did not vary significantly thereafter. These results showed a direct central effect of season on the regulation of basal concentrations of LH, modulated by a negative feed-back of ovarian secretions during the breeding season. In intact hares, the enhanced LH response after LHRH during the breeding season was related to an acute positive effect of ovarian secretions. The regulation of FSH was less dependent on season and remained under a negative control of the ovary throughout the year.     

Members of opposite sex mutually regulate gonadal recrudescence in the lizard Calotes versicolor Agamidae)

Adult males and females of the seasonally breeding lizardCalotes versicolor were subjected to various social situations under semi-natural conditions to explain the role of socio-sexual factors in gonadal recrudescence. They were grouped as: (i) males and females, (ii) males and females separated by a wire mesh, (iii) same sex groups of males or females, (iv) castrated males with intact females and (v) ovariectomized (OvX) females with intact males from postbreeding to breeding phase. Specimens collected from the wild during breeding season served as the control group. Plasma sex steroid levels (testosterone in male and 17β-estradiol in female), spermatogenetic activity and vitellogenesis were the criteria to judge gonadal recrudescence. In intact males and females that were kept together, gonadal recrudescence and plasma sex steroids levels were comparable to those in wild-caught individuals. Gonadal recrudescence was at its least in all male and all female groups, and plasma sex steroids were at basal levels. Association with OvX females initiated testicular recrudescence but spermatogenetic activity progressed only up to the spermatid stage while males separated from females by wire mesh showed spermatogenetic activity for a shorter period. Females grouped with castrated males and those separated from males by wire mesh produced vitellogenic follicles. However, the total number and diameter of vitellogenic follicles, and plasma estradiol levels were lower than in the females grouped with intact males. The findings indicate that association with members of the opposite sex with progressively rising titers of sex steroids is crucial in both initiating and sustaining gonadal recrudescence in the lizard. Thus, members of the opposite sex mutually regulate gonadal recrudescence in theC. versicolor.     

Resumption of seasonal breeding patterns in male and female rhesus monkeys transferred from an indoor to an outdoor environment

Seasonal aspects of social behavior and sex steroid levels were observed in two groups of rhesus monkeys from March through December. One group (3 males, 7 females) had lived outdoors for several years. The other group (6 males, 5 females), transferred outdoors in late February, had lived indoors for several years. In March-April, the long-term outdoor residents displayed the expected seasonal pattern of sexual behavior, characterized by absence of complete sequences of copulatory behavior. At this time the indoor-adapted group displayed high levels of copulatory behavior. Thereafter, frequencies of sexual behavior of the two groups were similar. Testosterone in the males was positively correlated with frequency of sexual behavior in each group. Females in the indoor-adapted group displaced menstrual cycles in March and April and 3 of 5 became pregnant at this time. The two remaining indoor-adapted females continued to display ovulatory cycles, but little sexual behavior, throughout the summer. Interestingly, two females in the outdoor-adapted group also displayed summer ovulatory cycles; without concomitant sexual activity. These data show that the disruption of seasonal breeding patterns produced by lengthy indoor housing remains briefly apparent following transfer outdoors, but is substantially overcome within a few months.     

Behavioural and hormonal responses of male rhesus monkeys introduced to females in the breeding and non-breeding seasons.

Six adult male rhesus monkeys were introduced individually to an all-female group for 10 days during the mating season. The initial aggressive responses of the females were rapidly replaced by positive social behaviour, and each male achieved alpha status and had access to social and sexual partners. A repetition of this paradigm in the non-breeding season produced significantly more female aggression, and no male attained high rank or engaged in sexual or other social behaviour. Male testosterone levels rose following introduction to the females in both seasons, but were significantly higher during the breeding season. Hormonal levels following removal from the females suggest a complex interplay between social, sexual and seasonal variables and recent social experiences. The differences in female social behaviour with newly introduced males, as a function of season, suggest an explanation for the seasonal limitation of male troop transfers.     

Tactile contact is required for early estrogen treatment to alter the sexual partner preference of female zebra finches

Sex steroid actions during early development appear to play a role in the development of sex differences in sexual partner preference (SPP, preference for males vs. females) in several species of mammals and in the socially monogamous pair bonding zebra finch (Taeniopygia guttata). Female finches treated with estrogen as nestlings exhibit varying degrees of masculinized SPP as adults, but only if they have been housed in all-female groups during the juvenile and young adult period, suggesting that the estrogen effect may involve social experience and possibly sexual imprinting. Because tactile contact is important for consolidation of imprinted preferences in this species, it was predicted that early estrogen treatment would alter preferences of females only if they were allowed to have tactile contact with other females. Subjects were injected with estradiol benzoate or with oil (normal controls) daily for the first 2 weeks post-hatching. At age 45 days, they were housed in a mixed sex aviary (normal controls), in an all-female aviary allowing tactile contact (group EB-TC), or in an all-female aviary with no tactile contact (group EB-NTC). At 100+ days, birds were given two-choice SPP tests followed by aviary tests of SPP. EB-TC females did not show the sex-typical preference for male stimuli, and differed significantly from the controls on several measures. EB-NTC females preferred males and never differed significantly from controls. These results show that tactile contact after age 45 days is essential for an EB effect on SPP, supporting the hypothesis that hormones and sexual imprinting together contribute to SPP.     

Male-female interactions of sika deer (cervus nippon) in nara park through allogrooming during breeding and rutting seasons

The frequency and pattern of interactions between males and females of sika deerCervus nippon were surveyed in 3 sites of Nara Park, central Japan, mainly via observation of allogrooming frequency and aggressive behavior throughout the breeding and rutting seasons. In the breeding season, the Daibutsuden group contained several adult males while Ukimido and Hakuba groups contained only a few. Most allogroomers were adult and subadult females. Females groomed the same sex more than the opposite sex at Daibutsuden, but at the other 2 sites, there was no such difference. In general, male-female interactions through allogrooming frequencies in the breeding season were not significantly fewer than intra-sex interactions. Males that attacked females tended to be groomed by females in the breeding season. In the rutting season, all adult males identified in the breeding season were absent at the usual observation sites, and newly arrived males showed defensive and/or mating behaviors. Females groomed adult males in the rutting season regardless of group status or display of sexual interactions. This suggests that male-female allogrooming in the breeding season does not relate to mating in the following rutting season, but may reduce tension in the group during the current breeding season.     

Adrenal contribution to the induction of sexual behavior in the female musk shrew.

Sexually experienced female musk shrews (Suncus murinus) lack an ovarian, vaginal, and behavioral estrous cycle. Females, once induced by their initial contact with a male, are able to display copulatory behavior whenever a male is present (Rissman, Silveira, and Bronson, 1988). Based on plasma levels of steroids, and on hormone replacement studies conducted after ovariectomy (OVX), we have shown that testosterone (T) plays an essential role in the regulation of female sexual behavior (Rissman and Crews, 1988; Rissman, Clendenon, and Krohmer, 1990a; Rissman, 1991). To date we have only examined the potential contribution of adrenal steroids to female sexual behavior in a preliminary manner. After adrenalectomy, gonadally intact females display significantly lower levels of sexual behavior than controls (Rissman and Bronson, 1987). The following experiments were conducted to examine the role the adrenal steroids (in contrast to the medullary hormones) play in the induction of female sexual behavior in the musk shrew. In the first experiment gonadally intact females were treated with dexamethasone (DEX) to reduce the secretion of adrenal steroids. Significantly fewer females receiving DEX demonstrated sexual behavior as compared with controls. In the second study, OVX females received T-filled Silastic implants. When DEX was administered to OVX + T females at a dose that dropped circulating T levels to those found in ovary and adrenal intact females, no effect on sexual behavior was noted. The data show that the adrenals are a behaviorally important source of T and contribute toward the hormonal control of sexual behavior in these female mammals.     

Seasonal variation in sexual behavior of all-male rhesus troops

Free roaming groups of Rhesus monkeys show a clear annual cycle in the incidence of sexual behavior. One hypothesis explaining the control of this cycle is that seasonal variables act directly on females, altering their endocrine status. Aroused females then communicate their sexual receptivity to male group members. The sexual behavior of 35 male Rhesus was observed during the non-mating and the mating season. All animals were maintained in large outdoor enclosures. One group of males (N = 7) were housed with females and juveniles as part of a breeding group. A second group of males (N = 8) had visual contact with the members of the breeding group, and a third group of males (N = 20) had no contact with either of these groups. During the non-mating season no sexual behavior was observed. At the onset of the mating season, the males with females displayed evidence of hormonal arousal and became sexually active. The males with visual contact with the breeding group also evidenced hormonal arousal and began engaging in male-to-male sexual activity. The males in the third group showed no sign of sexual arousal. These findings support the hypothesis that seasonal influences act only on females; and demonstrate that females can communicate their endocrine status to males, even without direct physical contact.     

Territorial aggression and hormones during the non-breeding season in a tropical bird

The hormonal control of territorial aggression in male and female vertebrates outside the breeding season is still unresolved. Most vertebrates have regressed gonads when not breeding and do not secrete high levels of sex steroids. However, recent studies implicate estrogens in the regulation of non-breeding territoriality in some bird species. One possible source of steroids during the non-breeding season could be the adrenal glands that are known to produce sex steroid precursors such as dehydroepiandrosterone (DHEA). We studied tropical, year-round territorial spotted antbirds (Hylophylax n. naevioides) and asked (1). whether both males and females are aggressive in the non-breeding season and (2). whether DHEA is detectable in the plasma at that time. We conducted simulated territorial intrusions (STIs) with live decoys to male and female free-living spotted antbirds in central Panama. Non-breeding males and females displayed robust aggressive responses to STIs, and responded more intensely to decoys of their own sex. In both sexes, plasma DHEA concentrations were detectable and higher than levels of testosterone (T) and 17beta-estradiol (E(2)). In males, plasma DHEA concentrations were positively correlated with STI duration. Next, we conducted STIs in captive non-breeding birds. Captive males and females displayed robust aggressive behavior. Plasma DHEA concentrations were detectable in both sexes, whereas T was non-detectable (E(2) was not measured). Plasma DHEA concentrations of males were positively correlated with aggressive vocalizations and appeared to increase with longer STI durations. We conclude that male and female spotted antbirds can produce DHEA during the non-breeding season and DHEA may serve as a precursor of sex steroids for the regulation of year-round territorial behavior in both sexes.     

Effect of melatonin on daily LH secretion in intact and ovariectomized ewes during the breeding season.

This study was conducted to find out whether daily LH secretion in ewes may be modulated by melatonin during the breeding season, when the secretion of both hormones is raised. Patterns of plasma LH were determined in luteal-phase ewes infused intracerebroventricularly (icv.) with Ringer-Locke solution (control) and with melatonin (100 microg/100 microl/h). Response in LH secretion to melatonin was also defined in ovariectomized (OVX) ewes without and after estradiol treatment (OVX+E2). Basal LH concentrations by themselves did not differ significantly before, during and after both control and melatonin infusions in intact, luteal-phase ewes. However, single significant (P<0.05) increases in LH concentration were noted during the early dark phase in the control and 1h after start of infusion in melatonin treated ewes. In both OVX and OVX+E2 ewes, melatonin decreased significantly (P<0.01, P<0.05, respectively) mean plasma LH concentrations as compared to the levels noted before the infusions. In OVX+E2 ewes, a single significant (P<0.05) increase in LH occurred 1h after start of melatonin treatment, similarly as in luteal-phase ewes. No significant differences in the frequencies of LH pulses before, during and after melatonin infusion were found in all treatments groups. In conclusion, melatonin may exert a modulatory effect on daily LH secretion in ewes during the breeding season, stimulating the release of this gonadotropin in the presence of estradiol feedback and inhibiting it during steroid deprivation. Thus, estradiol seems to be positively linked with the action of melatonin on reproductive activity in ewes.     

Sex differences in cortisol secretion after administration of an ACTH analogue in sheep during the breeding and non-breeding season

The aim of this study was to compare the response of cortisol in sheep of different sex and gonadal status to adrenal cortex stimulation by an ACTH analogue in the breeding and non-breeding season. Twenty-four adult Corriedale sheep were used in the non-breeding season, and 19 in the breeding season. Three weeks prior to the first trial (non-breeding season), six rams and six ewes were gonadectomised. In each trial, blood was obtained every 15min for 9h and the animals received 0.5mg of ACTH (Tetracosactid, Synacthen Depot i.m., after 1.5h of sampling. Sampling began at 10:00a.m. in the non-breeding season and at 9:00a.m. in the breeding season. Three main effects (sex, gonadal status and season) were evaluated, each with two levels (male and female, intact and gonadectomised, breeding and non-breeding season, respectively). In both seasons, the females showed higher cortisol levels after ACTH than males (P<0.001), though the difference seemed less marked in the non-breeding season. The cortisol response in the ewes was not affected by season. The rams, however, showed a lower response in the breeding season (P<0.03). Gonadectomy reduced the response in the ewes (P<0.001) but had no effect in the rams. Nevertheless, gonadectomy also eliminated the differences between the ewes and the rams, such that the intact rams had lower levels of cortisol compared to the intact females, with those of the gonadectomised animals of both sexes being intermediate between the gonad-intact groups. The results of this study confirm sex differences in ACTH induced cortisol secretion in intact sheep in vivo. Furthermore, by applying exogenous ACTH we have directly stimulated the adrenal cortex, indicating the existence of sex differences also at this level. The circulating gonadal steroids, which are responsible at least in part for the sex differences in the responses to stress, may influence cortisol secretion from the adrenal gland by direct action at the cortex.     

The effect of season on the induction of sexual behavior by estradiol in female rhesus monkeys

Rhesus monkeys housed in an outdoor environment are seasonal breeders, with ovulations and concomitant sexual behavior limited to the fall and winter months. To determine if there is a seasonal difference in the capacity of physiological levels of estradiol (E2) to induce sexual behavior in ovariectomized rhesus monkeys housed outdoors, subjects living in a social group were treated with subcutaneous E2 implants in a counter-balanced design during the nonbreeding season (May-July) and during the breeding season (September-November). Serum E2 levels were monitored by obtaining blood samples twice a week. Three levels of E2 were studied: baseline (less than 30 pg/ml), follicular (100 pg/ml), and periovulatory (200 pg/ml). Two of five adult males in the group were injected with human chorionic gonadotropin (hCG) twice a week to insure that males with high testosterone levels were present during each season. Focal observations of behavior of 15 minutes' duration on each subject were conducted 5 days per week, with frequencies and durations of social, sexual, and solitary behaviors recorded. Concomitant 2-h group scans were made to record all occurrences of mounting behavior. Neither heterosexual serial mounting nor seminal plugs were ever observed in E2-treated females during the summer months. In contrast, copulation and seminal plugs were observed in subjects at both treatment levels during the fall. While E2-treated females engaged in homosexual mounting behavior during both summer and fall, E2 treatment resulted in heterosexual copulation only during the fall. Changes in patterns of social behavior paralleled changes in sexual behavior and were significantly affected by treatment and season, with more male-female interactions during the fall months.(ABSTRACT TRUNCATED AT 250 WORDS)     

Physical provocation of pubertal anabolic androgenic steroid exposed male rats elicits aggression towards females

Human studies suggest that anabolic androgenic steroid (AAS) users are aggressive towards women. This study used a rat model to evaluate whether AAS potentiated aggression towards females and the conditions under which this occurs. Gonadally intact pubertal male rats received one of the following AAS treatments (5 mg/kg s.c. 5 days/week for nine weeks): testosterone (T), stanozolol (S), testosterone + stanozolol (T + S), or vehicle control. Each rat was tested with 3 conspecific stimuli: ovariectomized females (OVX), estrogen only females (E), and estrogen + progesterone females (E + P). The response to physical provocation was tested under three conditions: without physical provocation, provocation of the experimental male, and provocation of the conspecific female. Provocation was a mild tail pinch. Both aggressive and sexual behaviors were measured during each test. In the absence of physical provocation, AAS males were not aggressive towards females. However, provocation significantly increased aggression in males treated with testosterone but only towards OVX females. In the presence of E or E + P females, all animals displayed sex behavior, not aggression. Thus, factors such as the nature of the AAS and the hormonal status of the females are important in determining whether male rats will be aggressive towards females. However, the most salient factor determining aggression towards females is the presence of provocation in combination with high levels of testosterone.     

Induction of sexual receptivity in the female broad-headed skink, Eumeces laticeps, by estradiol-17 beta

Sexual receptivity in the female scincid lizard Eumeces laticeps occurs naturally only during the spring breeding season, which is also when maximal follicular development occurs. The presumption that high estrogen levels are coincidentally present and the need for a reliable method of inducing sexual receptivity for behavioral studies prompted tests of the hypothesis that estrogen induces sexual behavior. A series of experiments established that estradiol-17 beta induces sexual behavior. A series of experiments established that estradiol-17 beta induces sexual receptivity within 4 days when injected every other day at 2.0 micrograms in 20 microliters peanut oil in intact or ovariectomized females. In behavioral tests conducted during August, all control females (intact or ovariectomized injected with vehicle only) rejected courtship whereas all females receiving estrogen copulated. Estrogen injections also induced a statistically significant change from rejection to receptivity within individuals. Initial attempts to implant estradiol-17 beta in Silastic tubes killed all females so treated.     

Endocrine control of sexual behavior in sneaker males of the peacock blenny Salaria pavo: effects of castration, aromatase inhibition, testosterone and estradiol

The effects of castration and sex steroid manipulations on the expression of sexual behavior were investigated in a small fish, the peacock blenny, Salaria pavo. In this species, large males defend nests and attract females while small "sneaker" males reproduce by imitating the female morphology and courtship behavior in order to approach nests during spawning events and parasitically fertilize eggs. Sneakers switch into nest holders in their second breeding season, thus displaying both male and female-like sexual behavior during their lifetime. We tested the effects of castration and of an aromatase inhibitor (Fadrozole, F), testosterone (T) or 17beta-estradiol (E(2)) implants on the expression of male and female-like behavior in sneakers. Sneakers were either sham-operated, castrated or castrated and implanted with vehicle, F, T+F or E(2)+F. Seven days after the treatment, sneakers were placed in a tank with a nesting male, two ripe females and an available nest. Castrated fish had lower levels of circulating T and increased the time spent displaying female typical nuptial coloration. T implants had the opposite effect, inhibiting the expression of female-like behavior and coloration. E(2) implants had no significant effect on the display of sexual behavior but the frequency of aggressive displays decreased. The results agree with previous findings in sneakers of S. pavo that demonstrated an inhibition of female-like behavior by 11-ketotestosterone (11-KT). The reported increase in T and 11-KT production when sneakers change into nest holders may thus contribute to behaviorally defeminize sneakers. Contrarily, both T and E(2) failed to promote male-like behavior, suggesting that behavioral masculization during tactic switching depends on other neuroendocrine mechanisms or that the time length of the experiment was insufficient to induce male-like behavioral changes in sneakers.     

Estradiol increases somatomedin-C concentrations in adolescent rhesus macaques (Macaca mulatta)

Estradiol (E2) may enhance somatomedin-C (Sm-C) secretion during puberty in female rhesus monkeys. The present study evaluated the importance of age and acute changes in E2 on Sm-C secretion. Intact (INT) females at their first ovulation (age 3.5 yr; n = 6) had higher levels of Sm-C across the ovulatory cycle than did intact adults (ADT) (n = 5). Levels of Sm-C were similar for both groups during the follicular and luteal phases despite higher follicular phase levels of E2. Young, ovariectomized, E2-treated (E2OVX) females (age 3.5 yr; n = 5; E2 = 50 pg/ml) had higher basal levels of Sm-C than did either age-matched ovariectomized (OVX) females (n = 3), ovariectomized adults (OXA), or E2-treated ovariectomized adults (E2A) (E2 = 100 pg/ml). When ovariectomized groups were given E2 to induce ovulatory increases, no changes in serum Sm-C occurred. Comparisons among age-mates revealed that basal levels of Sm-C were similar between INT and E2OVX, yet these levels were higher than those for OVX. Sm-C levels were similar among all adult groups. Serum growth hormone (GH) was highest in E2OVX, next highest in INT and OVX, and lowest in all adults. Higher Sm-C levels in young animals are, thus, related to these age differences in GH concentrations and are further enhanced by basal levels of E2 and not by acute changes in this steroid. Low Sm-C secretion in adults is associated with low GH levels. Thus, the facilitory effect of basal E2 on Sm-C release is observed during conditions when basal GH levels are elevated, a situation normally limited to adolescence.     

Aggressive Behavior and Courtship Rejection in Brightly and Plainly Colored Female Keeled Earless Lizards (Holbrookia propinqua)

Relationships between bright secondary sexual coloration and behavior were studied in female Holbrookia propinqua, which develop striking orange and yellow colors during the breeding season. In tethered introduction studies, brightly colored females performed aggressive courtship rejection behaviors toward conspecific males; plainly colored females were not aggressive toward males, but attempted to avoid them. Responses of females of the two color patterns toward conspecific females of both color phases were not detectably different. Experimental introductions of lizards with coloration modified by paint showed that females of both color patterns recognize any other lizard bearing the bright female colors as female, regardless of actual sex. Both the orange and yellow components were shown to contribute to sex recognition. The yellow component alone allowed accurate sex identification, but only half the females responded to males painted with only the orange female component as if they were females. Because females did not behave differently toward other females on the basis of coloration, the hypothesis that bright coloration evolved as an adaptive signal between females is rejected. The dark ventrolateral stripes of male and plainly colored females did not appear to affect intraspecific social responses by females.     

Seasonal and sexual dimorphisms in the green anole forebrain

During the breeding season, male green anole lizards extend a throat fan (dewlap) in courtship. This behavior is facilitated by testosterone (T). Females extend a much smaller dewlap less often, even with the same dose of T. During the nonbreeding season when T is low, dewlap extension is reduced. To determine if parallels exist between structure and function, we investigated neuron soma size and density in the preoptic area (POA) and ventromedial nucleus of the amygdala (AMY), which are involved in the display behavior, in breeding and nonbreeding males and females. Cells from breeding animals were larger than cells from nonbreeding animals, but they were not sexually dimorphic. No significant effects existed in neuron density. This experiment indicates that portions of the anole forebrain important for sexual behavior are plastic and might be influenced by seasonal changes in steroid hormones. To investigate whether T can reverse the seasonal difference in soma size in both sexes, gonadectomized nonbreeding anoles were implanted with an empty or T propionate-filled capsule; animals were also tested for male-typical courtship behavior. Males and females treated with T had higher rates of dewlap extension, but across treatment groups these rates were greater in males. Neuron soma size in the POA and AMY was larger in males than females, but no effects of treatment were detected. Taken together, the results indicate that T can stimulate behavior in the nonbreeding season and suggest that a dissociation exists between the regulation of the courtship display and soma size of relevant brain regions.     

Sexual dimorphisms in a neuromuscular system regulating courtship in the green anole lizard: effects of season and androgen treatment.

During the breeding season, male green anoles (Anolis carolinensis) court females by extending a red throat fan called a dewlap. Motoneurons controlling this sexually dimorphic behavior are located in two portions of the brain stem: (a) the vagal portion of nucleus ambiguus (AmbX), and (b) the region containing the glossopharyngeal portion of nucleus ambiguus and the ventral motor nucleus of the facial nerve (AmbIX/VIImv). These motoneurons project to the ceratohyoideus muscle via the ramus pharyngo-laryngeus IX+X. To investigate the effects of season on and androgen regulation of neural and peripheral structures controlling dewlap extension, two experiments were conducted: (a) During the breeding and nonbreeding seasons, motoneuron number, soma size, and nucleus size were investigated in intact males and females and in castrated males treated with a testosterone propionate (TP) or a blank Silastic capsule. (b) Cross-sectional area of the nerve and muscle fiber size, number, and density were investigated in the four treatment groups during the breeding season only. No significant differences were found in motoneuron number. In the breeding season, subtle male-biased sex differences existed in both AmbX and AmbIX/VIImv soma size. Nerve cross-sectional area and muscle fiber size and number were substantially larger in males than females. Muscle fiber density was higher in females. No consistent effects due to season or androgen treatment were detected, although characteristics of motoneurons were in some cases slightly larger in the nonbreeding season. These results suggest that, while parallels to behavior exist between the sexes, morphological changes in adulthood in the dewlap motoneurons and muscle do not normally regulate courtship behavior in the male green anole.     

Progesterone as a predictor of cyclicity in Bolivian squirrel monkeys during the breeding season

In a squirrel monkey breeding colony, two distinct groups of females were observed during the breeding season, December through March. One had low and the other had high estradiol (E2) and progesterone (P) concentrations. The conception rate in females with high E2 and P values was 74%. However, only 25% of monkeys with low steroid concentrations became pregnant during the breeding season. This study showed that all mature females in a colony may not be cycling concurrently and that two serum P measurements obtained at four-day intervals may be utilized to detect noncycling monkeys during the breeding season.