Social factors modulate the effects of hormones on the sexual and aggressive behavior of macaques

We previously reviewed the effects of gonadal hormones on the sexual and aggressive behavior of macaques as observed in field, outdoor colony, and laboratory studies. There were consistent similarities between findings from different observational settings, but there were also noteworthy differences which suggested the importance of social and environmental factors in modulating the effects of hormones. We now examine the role of these factors further and consider the extent to which partner preferences, familiarity between individuals, and also dominance rank can affect the behavior of male-female pairs and thereby modify the influences of hormones. The evidence suggests that all these factors are important. Hormone-dependent short-term partner preferences appear to be critical for the formation of consort bonds and to facilitate mating between unfamiliar partners. Socially based partner preferences tend to dampen hormonal influences and may lead to long-term familiarity. Long-term familiarity decreases sexual interactions and may be a proximate mechanism underlying incest avoidance and periodic male troop transfers. Both males and females exhibit mate competition under certain conditions, and their dominance rank can modify sexual and aggressive behavior by either optimizing or reducing hormone-dependent changes. These interaction effects between social and hormonal variables also have relevance for the design and interpretation of laboratory experiments. © 1996 Wiley-Liss, Inc.     

Perceived environmental threats as a factor in reproductive behavior: an examination of American youth

This study presents a test of general life history theory by estimating the association between perceived environmental threat (PET) and reproductive outcomes among American youth. Data for the study came from the National Longitudinal Survey of Youth 1997–2009, which consists of a nationally representative sample of youth. Analyses were based on a subsample of N= 4748 respondents who were aged 12–14 years in 1997; reported having no biological children in 1997; and, for females, were not pregnant at the time of the 1997 interview. PET was measured using 11 questionnaire items that asked respondents about experiences with violent assaults from peers, witnessing violent assaults, and nonviolent crime victimization. First childbirth occurred earlier among respondents who reported higher PET in 1997. Average fertility during the study period was also higher among respondents with higher PET. Male and female respondents' reproductive behaviors were similarly associated with PET. However, only among female respondents was the association between PET and fertility moderated by the quality of the household environment.     

Oxytocin in the medial preoptic area facilitates male sexual behavior in the rat

Oxytocin (OT) is a versatile neuropeptide that is involved in a variety of mammalian behaviors, and its role in reproductive function and behavior has been well established. The majority of pharmacological studies of the effects of OT on male sexual behavior have focused on the paraventricular nucleus (PVN), ventral tegmental area (VTA), hippocampus, and amygdala. Less attention has been given to the medial preoptic area (MPOA), a major integrative site for male sexual behavior. The present study investigated the effects of intra-MPOA administration of OT and (d(CH2)51, Tyr(Me)2, Thr4, Orn8, Tyr-NH29)-vasotocin, an OT antagonist (OTA), on copulation in the male rat. The relationship between OT receptor (OTR) binding levels in the MPOA and sexual efficiency was also explored. Microinjection of OT into the MPOA facilitated copulation in sexually experienced male rats, whereas similar injections of an OTA inhibited certain aspects of copulation but had no significant effect on locomotor activity in an open field. Contrary to expectation, sexually efficient males had lower levels of OTR binding in the rostral MPOA compared to inefficient animals. The present data suggest that OT activity in the MPOA is not necessary for the expression of male sexual behavior but is sufficient to facilitate copulatory behaviors and improve sexual efficiency in sexually experienced male rats. These data also suggest that OTR activity in the MPOA stimulates anogenital investigation, facilitates the initiation of copulation, and plays a role in the sensitization effect of the first ejaculation on subsequent ejaculations.     

The influence of androgenic and estrogenic hormones on sexual behavior in castrated adult male pigs

The objectives of these studies were to evaluate the influence of testosterone propionate (TP), estradiol cypionate (EC), dihydrotestosterone propionate (DHTP), EC + TP, EC + DHTP, and TP + DHTP on traits of masculine sexual behavior in castrated adult male pigs of different breeds. Masculine sexual behavior was restored and maintained by TP, whereas EC initially activated sexual behavior, including copulation and ejaculation, but was unable to sustain copulatory behavior for the 8- to 18-week periods that were evaluated. Treatment with DHTP was ineffective for stimulation of sexual behavior; thus, it is suggested that testosterone promotes some aspects of masculine sexual behavior in male pigs via aromatization to estrogen, but both androgen and estrogen are required for maintenance of the full complement of masculine sexual behavior traits.     

Social influence on sexual maturation and breeding in the female Mongolian gerbil (Meriones unguiculatus)

Social factors influencing reproductive activity in laboratory groups of gerbils were investigated using the ventral scent-gland as an index of reproductive condition. Sexual maturation and breeding were suppressed in female offspring remaining with their parents. In family groups living in enclosures, daughters rarely bred in the presence of their mother but breeding activity increased after death. Intra-female aggression resulted in the re-establishment of a single breeding female in groups where more than one started to breed. In a controlled social situation in which females were caged with their mothers, sexual maturation was suppressed in the presence of their mother and the continuing presence of her second litter, but not in the presence of a non-pregnant mother or a mother whose second litter had been removed.     

Role of septum and preoptic area in regulating masculine and feminine sexual behavior in male rats

The effects of septal or preoptic lesions on both masculine and feminine sexual behaviors were examined in castrated adult male rats. Three weeks after brain surgery, animals were implanted with Silastic tubes containing testosterone (T) and observations of masculine sexual behavior were carried out four times every 5 days. T tubes were removed immediately after the end of the masculine behavioral tests. Two weeks later, animals implanted with Silastic tubes containing estradiol-17 beta(E2) were subjected to three feminine sexual behavioral tests at 5-day intervals. The bilateral lateral septal lesion (LSL) and the medial preoptic lesion (MPOL) effectively suppressed the performance of mounts, intromissions, and ejaculations, whereas the medial septal lesion (MSL), the dorsolateral preoptic lesion (DPOL), and the sham operation did not show any significant suppression of these behaviors. In the feminine sexual behavioral tests, intact and sham-operated control males showed only a low lordotic activity. However, the performance of the lordosis reflex was markedly facilitated by LSL or DPOL, while the lordotic activity of MSL and MPOL males was not significantly different from that of control males. These results suggest that the lateral septum exerts not only a facilitatory influence on masculine sexual behavior but also an inhibitory influence on feminine sexual behavior in male rats. On the other hand, the medial preoptic area may play a critical role in regulating masculine sexual behavior in male rats.     

The influence of evolution and plasticity on the behavior of an invasive crayfish

Invasion success can be enhanced by evolution and behavioral plasticity, but the importance of these processes for most invasions is not well understood. Previous research suggests there is a genetic basis for differences in growth rate between native and invaded range rusty crayfish (Orconectes rusticus). We hypothesized that invaded range O. rusticus achieve faster growth by allocating more time to foraging and less to defense. We conducted a laboratory experiment to test the effects of range (native or invaded) and plasticity (as induced by exposure to predators) on crayfish behavior. We collected O. rusticus adults and eggs from both ranges, hatched eggs in the lab, and reared juveniles in common conditions either with or without predatory fish. We then quantified adult and juvenile crayfish activity in an experiment with and without predatory fish. In support of our hypothesis, invaded range adults displayed reduced antipredator behavior compared to native range adults. Further, invaded range juveniles were more active than native range juveniles without predators, but all juveniles were inactive with predators. In addition, invaded range juveniles had greater plasticity in behavior than native range juveniles. These results suggest that activity level in the absence of predators has diverged in the invaded range. Because active crayfish consume more prey, this change in behavior may be responsible for rapid growth in the invaded range of O. rusticus, a trait that contributes to the strong ecological impacts of this invasive crayfish.     

Sexual deprivation and its influence on testosterone levels and sexual behavior of old and middle-aged rhesus males

After approximately 6 mo without access to a receptive female, eight old (19 to 25 yr) and eight middle-aged (9 to 15 yr) males were given nine daily 10-min tests of sexual behavior with receptive females. Three ovariectomized, estrogen-primed females served as partners. Blood samples were taken from the males at 0900 and 2100 h on 2 consecutive days before and after the series of nine behavioral tests. Serum levels of testosterone (T) were measured by means of radioimmunoassay. There were no significant differences between serum T levels after 6 mo of sexual deprivation and after the nine tests of sexual behavior, nor did serum T levels differ between middle-aged and old males. Serum T levels were significantly higher in the 2100-h samples than in the 0900-h samples for both groups. The nocturnal increases in serum T, both absolute amounts and percentages of increase, did not differ between middle-aged and old males. Repeated daily testing had little effect on the major components of male sexual behavior. Middle-aged males outperformed old males; middle-aged males had higher rates of contracting the female, mounting and intromitting. They ejaculated earlier and had a greater percentage of tests with ejaculations than did old males.     

大学生性知识和性行为调查分析

目的:了解大学生性知识、性行为情况,以提高大学生性教育的针对性和质量.方法:对600名18-24岁的大学生志愿者进行关于性传播疾病(STD)、性知识和性行为的问卷调查,通过调查结果探讨大学生性教育存在的问题和解决方案.结果:所有大学生对性传播疾病的名称比较熟悉,但对性传播疾病的症状和传播方式了解不多或有误解,性知识水平较低.大部分大学生没有接受过正规的性教育,对未婚同居和婚前性行为持开放态度,性知识主要来源于书籍和网络.大学生们认为性教育很有必要.结论:大学生性和生殖健康知识贫乏,年轻的大学生应当对他们可能遇到的常见的性传播疾病有所了解.大学生性教育应更加侧重于性传播疾病的传播途径及预防.     

Social cues influence growth and sexual maturation of the male musk shrew (Suncus murinus)

Musk shrews were maintained from weaning (20 days of age) for 20 or 40 days in one of several social conditions. In Exp. 1, young males housed with adult females gained more weight and had heavier sex accessory organs than did young males housed with an adult male or reared alone. In Exp. 2 this same pattern of accelerated growth and sexual maturation was found when males were reared directly with an adult female or in a split cage where a wire barrier served to separate the male and his adult female cagemate. In Exp. 3, males were reared in cages containing clean or soiled bedding: soiled bedding was taken once every 5 days from the cage of an adult male, or a female. Under these conditions differences in the weights of reproductive tissues showed minimal variation with housing condition after 20 days of treatment. At that time males reared in soiled bedding taken from the cage of an adult female had accelerated development compared with control males. In Exp. 4, males were housed alone or in a split cage with an adult female which was separated by a wire mesh or a solid, opaque barrier. Males separated by a solid barrier from their female cagemates for 40 days had reproductive tissue weights equivalent to those measured in males reared alone. Taken together these results suggest that the presence of an adult female has dramatic effects on body growth and development of reproductive target tissues in young male musk shrews. Male-female social interactions could play an important role in the timing of puberty in this opportunistically breeding tropical mammal.     

Testosterone metabolism and sexual behavior in the chick

A series of experiments was performed to study the behavioral and physiological activity of testosterone (T) metabolites which are produced by neural tissues of male chicks, i.e., mainly 5α- and 5β-dihydrotestosterone (5α-, 5β-DHT), 5α- and 5β-androstan-3α, 17β-diol (5α-,5β-diol), and 4-androstene-3,17-dione (Δ4). It was found that 5β-reduced androgens alone or in combination with estradiol stimulate juvenile copulation in the chick while they have no detectable effect on all somatic variables which are recorded (testicular weight, plasma LH) with the exception of comb size. On the contrary, comb size was increased by T, Δ4, 5α-DHT, and 5α-diol while testis growth was prevented by T and Δ4 only. There is a good correlation between the anatomical localization of the enzymatic activities which metabolize T and the hormonal dependence of the biological responses: The comb converts T into 5α-reduced compounds which affect comb growth. 5β-Reduction is high in the hypothalamus, a fact which can be related to the sensitivity of sexual behavior to 5β-reduced androgens. This suggests that T metabolism is a very important step in the expression of this hormone's physiological effects.     

Impotence and abnormal sexual behavior in the stallion

Clinical observations have been made on stallions exhibiting impotence and other abnormal forms of sexual behavior. Procedures for diagnosing and retraining consisted of presenting the patient to one or more estrcus mares and observing his sexual behavior. Following sufficient observations, patients were classified into one or more of the following categories: (a) failure to obtain or maintain an erection; (b) incomplete intromission, or lack of pelvic thrusts after intromission; (c) dismounting at onset of ejaculation; (d) failure to ejaculate despite a complete, prolonged erection and repeated intromissions; and (e) ejaculate normally for several ejaculates, then cannot ejaculate without sexual rest, although libido remains high.To successfully diagnose and treat patients with abnormal sexual behavior the following are needed: (a) a variety of mares in estrus; (b) other stallions to provide a competitive environment; (c) a phantom; (d) an artificial vagina and laboratory equipment for seminal evaluation; and (e) extreme patience.Selected clinical cases are presented, including history, diagnosis and treatment with recommendations in relation to reproductive management. Some of the more important observations were: (a) impotence was often diagnosed as aspermatogenesis, due to failure of the impotent stallion to ejaculate; (b) erection was not always essential for ejaculation; (c) pain from injury or disease was often the etiology of abnormal sexual behavior; (d) in excess of 125 ml of semen were collected from a stallion without the occurrence of complete ejaculation; (e) the presence of gelatinous material (gel) in the semen did not necessarily mean complete ejaculation occurred; (f) occasionally seminal emissions from some stallions contained spermatozoa, usually nonmotile, with a large proportion of morphologically abnormal forms, without complete ejaculation.It was concluded that the most common cause of abnormal sexual behavior was mismanagement, such as excessive use, abusive training procedures, injuries during breeding, etc. The majority of the stallions responded well to retraining and recovery was essentially complete without the use of drugs.     

Social competition among gynes in halictine bees: The influence of bee size and pheromones on behavior

Solitary gynes of two species of social bees, Lasioglossum (Evylaeus) malachurumand L. (E.) pauxillum(Hymenoptera: Halictidae), were observed in the field and in the laboratory during the solitary (spring) phase of their life cycles. Fighting over nests among gynes of the former species is common when nests are being provisioned and can result in serious injury or even death to one or both interactants. The payoff is occasional acquisition of a nest. In contrast, fighting was never observed in the field among gynes of L. pauxillum.Several factors determine the outcome of such fights in L. malachuram,these include relative sizes of the two opponents as well as nest ownership. Dyadic interactions in the laboratory reveal that size influences the behavioral strategies of the gynes of both species, with the larger of two individuals in a dyadic interaction being on average more aggressive. Furthermore, in a second experimental series with L. malachurum,application to the smaller gyne of synthetically derived macrocyclic lactones found in the species' Dufour's gland pheromone mixture significantly decreased the aggressive tendencies of the larger such that its behavior was no longer significantly different from that for the smaller gyne. Therefore, among gynes, aggressive pheromonal signaling, coupled with other possible signal modalities, is probably an integral part in the communication system.     

Hypertension in Brattleboro rats and the injurious influence of salt in youth

The effect of long-term intake of 0.6% NaCl solution on survival of Brattleboro rats, both homozygous for diabetes insipidus (DI) and heterozygous (non-DI), was investigated. Studies included whether the survival of animals could be influenced a) by the age at which the high salt intake started (either from prepuberty, i.e. from the 4th week, or after sexual maturation, i.e. from the 12th week of age); b) by uninephrectomy (UNX) which elicited hypertension in DI rats drinking saline from youth. All non-DI and those DI rats that drank saline only from adulthood, survived for the whole duration of the experimental, i.e. 14 weeks. Only 43% of animals survived in the group of DI rats drinking saline from youth. This high mortality was reduced by UNX carried out either simultaneously or 8 weeks after the onset of saline drinking. DI rats consumed several times more saline than non-DI rats. Nevertheless, the consumption was greater in the low-mortality than in the high-mortality group. Salt intake was moderately lowered by UNX. Plasma Na+ concentration was higher in rats of the high-mortality group and it was not affected by UNX. In DI rats plasma volume was greater than in non-DI rats and its values in the low-mortality group exceeded those ones of the high-mortality group. It was decreased by UNX in the low-mortality group but this was not true for the high-mortality group. It is concluded that high mortality in DI rats consuming saline from prepuberty is abolished by the intervention producing hypertension. The role of hypertension in a protection against the toxic effects of salt is discussed.     

Social signals influence hormones independently of calling behavior in the treefrog (Hyla cinerea)

Social signals play an important role in regulating hormone-behavior relationships. In anurans (frogs and toads), acoustic signals are an essential aspect of reproductive behavior; however, the physiological consequences of receiving social signals has remained largely undescribed. Each night for 5, 10, or 20 days, we presented acoustically isolated male treefrogs with a conspecific mating chorus, an array of tones, or no sound. We recorded calling rate of individuals throughout the experiment and collected blood before and after treatment. Days of stimulus exposure had no effect on any dependent measure. Acoustic treatment influenced steroid levels; testosterone, dihydrotestosterone, and corticosterone increased only in the group exposed to the chorus. Chorus-exposed males also showed an increase in stimulus-evoked calling. We found no correlation between androgens and calling within each treatment group. In addition, noncallers in the chorus group had higher levels of androgens than males in the tone or no sound groups. Further, chorus-exposed males with zero, low, or high rate of calling had similar levels of androgens. These data indicate that social signals increase circulating androgens independently of calling behavior. Elevated corticosterone associated with chorus reception did not inhibit calling behavior, and corticosterone showed no correlation with androgen levels.