Effect of progestins on serum hormones,semen production,and agonistic behavior in the gerenuk (Litocranius walleri walleri)

The use of progestins to suppress endogenous testosterone production to reduce agonistic behavior and prevent semen production was studied in gerenuk. Five male gerenuk (20 months to 3 years of age), housed as a bachelor group, were treated with 3 monthly injections of medroxyprogesterone acetate (MPA; 2.5–20 mg/kg), followed by a melengestrol acetate implant (MGA; 0.3 g/kg) for 2 months. Blood samples collected monthly were assayed for serum testosterone and cortisol using enzyme‐linked immunoassays. Quantitative behavioral data were collected for 30 min 3/week starting 1 month before treatment. Body weight, testes volume, and semen traits were measured before treatment, after MPA treatment, and after MGA treatment. Results showed lower (P<0.05) mean serum testosterone concentrations after MPA (4.34 pg/ml) and MGA (5.02 pg/ml) treatment compared to pre‐treatment values (65.9 pg/ml) in four of five gerenuk. The remaining sub‐adult gerenuk had low testosterone initially (4.9 pg/ml) that did not decrease further with treatment (1.4 and 7.8 pg/ml for MPA and MGA, respectively). Mean serum cortisol concentrations decreased markedly after treatment with MPA (6.0±3.7 ng/ml) and MGA (0.8±0.3 ng/ml). Cortisol concentrations were regained rapidly post‐treatment (42.8±4.8 ng/ml) and were not significantly different from the pre‐treatment value (60.6±12.6 ng/ml; P>0.05). The mean incidence of combined aggressive/dominant behaviors (horning, sparring, supplanting, threat) was not different before and after treatment. Body weight, total numbers of spermatozoa produced per ejaculate, percent motility, and percent normal spermatozoa declined maximally 8 months after treatment. Mean testes volume decreased (P<0.05) after MGA treatment (10.53 cm³vs. 11.96 cm³ pre‐treatment). Elevated hepatic enzymes and bile acids were seen in three of five animals after progestin treatment and anorexia was noted in two males after MGA implant removal, however two of three males had elevated liver enzymes before progestin treatment began. Results show that reducing serum testosterone concentration does not seem to modify agonistic behavior in bachelor gerenuk groups. Zoo Biol 26:245–257, 2007. © 2007 Wiley‐Liss, Inc.     

Neighbor effects in marmosets: social contagion of agonism and affiliation in captive Callithrix jacchus

Researchers have demonstrated the neighbor effect for affiliative and agonistic neighbor vocalizations in captive chimpanzees. We extend the investigation of the neighbor effect to New World monkeys, Callithrix jacchus. We collected data on vocalizations and behaviors of 31 focal individuals and concurrent neighbor vocalization within three behavioral categories: intragroup and intergroup aggression and intragroup affiliation. We investigated whether there was an influence of neighbor vocalizations on focal behavior within the same behavioral category. For data analysis we used approximate randomization of paired‐sample t‐tests. We found that marmosets performed intergroup aggressive behavior (bristle, anogenital present for neighbor loud shrill only) for significantly longer, and emitted significantly more intergroup agonistic vocalizations (twitter, loud shrill), at a high frequency of intergroup agonistic neighbor vocalizations (twitter, loud shrill) than at low. The marmosets were also significantly more likely to engage in bristle behavior immediately after hearing a neighbor intergroup aggressive call (twitter, loud shrill) than directly beforehand. High neighbor intragroup agonistic calls (chatter) were associated with significantly longer spent in related behavior (composite of: attack, chase, steal food). Affiliative behaviors (share food, grooming invite) were engaged in by marmosets for significantly longer at higher frequencies of affiliative neighbor chirp calls than at low. Marmosets were also significantly more likely to perform food sharing and active affiliative contact immediately after rather than before hearing a neighbor chirp call. Our findings suggest that neighbor vocalizations influence marmoset behavior through social contagion and indicate that the neighbor effect for affiliation and aggression generalizes to the marmoset. Am. J. Primatol. 72:549–558, 2010. © 2010 Wiley‐Liss, Inc.     

Neurobiological correlates premeditated (learned) aggression: seeking new experimental approaches]

Theoretical possibility of experimental modeling of learned (premediated) aggression developing in human after experience of aggression is considered. The sensory contact technique increases aggressiveness in male mice and allows aggressive type of behavior to be formed as a result of repeated experience of victories in daily agonistic confrontations. Some behavioral domains confirm the development of learned aggression in males similar to those in humans. The features are: repeated experience of aggression reinforced by victories; elements of learned behavior after period of confrontations; intent, measured by increase of the aggressive motivation prior agonistic confrontation; decreased emotionality estimated by parameters of open field behavior. Relevant stimuli provoke demonstration of aggression. This review summarized data on the influence of positive fighting experience in daily intermale confrontations on the behavior, neurochemistry and physiology of aggressive mice (winners). This sort of experience changes many characteristics in individual and social behaviors, these having been estimated in different tests and in varied situations. Some physiological parameters are also changed in the winners. Neurochemical data confirm the activation of brain dopaminergic systems and functional inhibition of serotonergic system in winners under influence of repeated experience of aggression. The expression of the neurochemical and behavioral changes observed in winners has been found dependent on the mouse strain and on the duration of their agonistic confrontations. Similarities in mechanisms of learned aggression in humans and mice are considered.     

Effect of spatial crowding on aggressive behavior in a bonobo colony

According to a previously proposed coping model (De Waal [1989] Zoo Biol. 1(suppl):141–148), gregarious primates will react to crowding by adjusting their behavior in order to limit the amount of aggression displayed. Depending on the duration of the crowding, this can be achieved by the use of different strategies. Chimpanzees (Pan troglodytes) react to a medium‐term duration of spatial crowding by an active tension‐reduction mechanism whereby allogrooming markedly increases while aggression rises only slightly. Under comparable circumstances, a similar increase in grooming is found in bonobos (Pan paniscus). However, to test the coping model for bonobos, data on aggressive behavior during crowding are indispensable. This study provides such information by comparing the aggressive repertoire of a well‐established bonobo colony during a crowded period in winter with those that occurred during an uncrowded control period in summer. Given that during winter the aggression rate differed between food and nonfood contexts, we accounted for a potential effect of food context on aggression. During the crowded period, a significantly higher total frequency of aggression was found than during the control period. However, this increase was small in relation to the reduction in space when compared to similar experiments in other species. Together with observations of increased grooming under crowded conditions, our data confirm the hypothesis that bonobos cope with the increase in tension created by crowding (medium‐term duration) by applying a tension‐reduction strategy. Our data further show that although not all aggressive behaviors appear to be influenced by a high‐density condition, bonobos do not specifically limit their aggressive behaviors to mild, nonprovocative aggressions in a crowded environment. Zoo Biol 23:383–395, 2004. © 2004 Wiley‐Liss, Inc.     

Seasonal dynamics of agonistic behavior and hormones in an ex situ all‐male colony of large flying foxes

Large flying foxes (Pteropus vampyrus) are a socially complex species. In situ colonies typically comprise thousands of individuals in small harems of one male to many females. In ex situ environments, all‐male colonies are becoming more common due to a surplus of males in the population. There is limited information describing the hormonal and behavioral patterns of all‐male colonies during the breeding season. We assessed seasonal changes in hormones and behavior in an all‐male colony of 12 large flying foxes at Disney's Animal Kingdom^®. We validated hormone assays using morning urine and fecal samples to assess seasonal changes in excreted immunoreactive testosterone and glucocorticoid metabolites. We collected behavior data using an all‐occurrence method, recording agonistic behaviors related to territorial defense (hooking, biting, wing flexing, vocalizing, and wrestling), and sexual behavior (mounting and frontal grabbing). Results indicated that (i) we could reliably measure testosterone and glucocorticoid metabolites concentrations from fecal and urine samples collected from individual bats; (ii) there were distinct relationships between changes in levels of agonism and hormone concentrations throughout the year; and (iii) three agonistic behaviors (chasing, wrestling, and open‐mouth threat) peaked prior to the increase in testosterone and glucocorticoid hormones measured during the breeding season. These three behaviors could potentially be used as early indicators to signal the onset of the breeding season and allow time to implement ex situ management changes to reduce the incidence of agonism between individuals.     

Social interactions and aggression among male Madagascar hissing cockroaches (Gromphadorhina portentosa) in groups (Dictyoptera: Blaberidae)

We studied agonistic interactions among male Madagascar hissing cockroaches,Gromphadorhina portentosa, in groups of five (low-density) or 10 (high-density) males. Consistent with previous studies of male pairs, we observed aggression (Abdomen Flick, Abdomen Push, Butt, Lunge), submission (Crouch, Retreat), and noncontact behavior (Abdominal Extension, Abdomen Thrash, Agonistic Hiss, Stilt). Males at both densities performed all acts. However, males in the high-density group performed Abdomen Push significantly more often than males at a low density. The rate of each remaining act was unaffected by density. Regardless of density, males within social groups varied in aggression. More aggressive males utilized frontal assaults (Butt and Lunge) during interactions, while males displaying lower levels of aggression preferentially used the abdomen during interactions. More aggressive males performed Abdomen Flick more frequently, while males displaying lower levels of aggression performed Abdomen Push. We also investigated the relationship between male aggression and the four noncontact behaviors. We found that Abdominal Extension, Abdomen Thrash, and Agonistic Hiss were positively correlated with our aggregate measure of male aggression suggesting these are aggressive displays. Stilt was positively correlated with measures of both aggression and submission, leaving its function unclear. None of the behavioral acts examined in this study were highly correlated with male weight. Our results are discussed in light of possible hypotheses addressing the function of specific behavior during male-male competition.     

Interactions between behavior and plasma steroids within the scramble mating system of the promiscuous green turtle, Chelonia mydas.

We measured plasma androgen (combined testosterone and 5alpha-dihydrotestosterone) (A) and corticosterone (B) in the promiscuous green turtle (Chelonia mydas) during courtship in the southern Great Barrier Reef. This study examined if reproductive behaviors and intermale aggression induced behavioral androgen and adrenocortical responses in reproductively active male and female green turtles. Associations between reproductive behavior and plasma steroids were investigated in green turtles across the population and within individuals. Levels across a range of both asocial and social behaviors were compared including (a) free swimming behavior; (b) initial courtship interactions; (c) mounted behavior (male and female turtles involved in copulatory activities); (d) intermale aggression (rival males that physically competed with another male turtle or mounted males recipient to these aggressive interactions); and (e) extensive courtship damage (male turtles that had accumulated excessive courtship damage from rival males). Behavioral androgen responses were detected in male turtles, in that plasma A was observed to increase with both attendant and mounted behavior. Male turtles who had been subjected to intermale aggression or who had accumulated severe courtship damage exhibited significantly lower plasma A than their respective controls. No pronounced adrenocortical response was observed after either intermale aggression or accumulation of extensive courtship damage. Female turtles exhibited a significant increase in plasma B during swimming versus mounted behavior, but no change in plasma A. We discuss our results in terms of how scramble polygamy might influence behavioral androgen interactions differently from more typical combative and territorial forms of male polygamy.     

Fine‐ and Broad‐Scale Approaches to Understanding the Evolution of Aggression in Crickets

Male field crickets frequently engage in agonistic contests to establish dominance in social interactions and gain access to mate attraction territories. Crickets (Orthoptera: Gryllidae) are often used as a model taxon to study aggression, but limited documentation of aggression in some cricket species hinders our understanding of its evolutionary costs and benefits. Our study investigated cricket aggression at two scales: the within‐species scale for two cricket species, Gryllus assimilis and G. veletis, whose aggression had not been adequately documented and the among‐species scale to detect evolutionary patterns in species’ levels of aggression. In both G. veletis and G. assimilis, winners spent more time being aggressive than losers, but they were not larger or heavier. Collectively, our results reveal that G. veletis males are more aggressive than G. assimilis. Male G. veletis had higher aggression scores that male G. assimilis. The majority of G. veletis contests escalated to grappling (a highly aggressive behavior), while less than one quarter of G. assimilis contests escalated to grappling. Further, G. veletis males transitioned between two of the most aggressive behaviors most often while G. assimilis transitioned between two of the least aggressive behaviors most often. We integrate this new information on aggression for G. assimilis and G. veletis with previously documented aggression data for many cricket species to investigate aggression in a broader evolutionary context than previously possible. Within a phylogenetic context, we test the hypothesis that species whose males use burrows from which to call and attract females are more aggressive than species with non‐burrowing males. We found evidence consistent with this hypothesis; species with burrowing males tended to be more aggressive than species with non‐burrowing males. Together, our study provides fine‐scale understanding of aggression in two cricket species and broad‐scale evolutionary context for aggression across cricket species.     

Raphe serotonin neuron‐specific oxytocin receptor knockout reduces aggression without affecting anxiety‐like behavior in male mice only

Serotonin and oxytocin influence aggressive and anxiety‐like behaviors, though it is unclear how the two may interact. That the oxytocin receptor is expressed in the serotonergic raphe nuclei suggests a mechanism by which the two neurotransmitters may cooperatively influence behavior. We hypothesized that oxytocin acts on raphe neurons to influence serotonergically mediated anxiety‐like, aggressive and parental care behaviors. We eliminated expression of the oxytocin receptor in raphe neurons by crossing mice expressing Cre recombinase under control of the serotonin transporter promoter (Slc6a4) with our conditional oxytocin receptor knockout line. The knockout mice generated by this cross are normal across a range of behavioral measures: there are no effects for either sex on locomotion in an open‐field, olfactory habituation/dishabituation or, surprisingly, anxiety‐like behaviors in the elevated O and plus mazes. There was a profound deficit in male aggression: only one of 11 raphe oxytocin receptor knockouts showed any aggressive behavior, compared to 8 of 11 wildtypes. In contrast, female knockouts displayed no deficits in maternal behavior or aggression. Our results show that oxytocin, via its effects on raphe neurons, is a key regulator of resident‐intruder aggression in males but not maternal aggression. Furthermore, this reduction in male aggression is quite different from the effects reported previously after forebrain or total elimination of oxytocin receptors. Finally, we conclude that when constitutively eliminated, oxytocin receptors expressed by serotonin cells do not contribute to baseline anxiety‐like behaviors or maternal care.     

The effect of DAGO,selective milli-opioid receptor agonist,on hostile and anxious behaviors in male mice with different experience of aggression

Effects of mu-opioid receptor agonist DAGO (2.0 mg/kg, s.c.) on anxioUs, hostile, and aggressive behaviors of male mice with repeated 3- and 20-day experience of aggression accompanied by victories (T3 and T20 winners, respectively) were stUdied. T20 winners showed lower aggression (attacking and biting) and hostile behavior and were more anxioUs (estimated by plUs-maze test) than T3 winners. In the plUs-maze test DAGO prodUced anxiogenic effects in intact males and was ineffective in T3 and T20 winners testifying to a decrease in mu-receptor sensitivity Under the inflUence of repeated aggression. In agonistic confrontation test, DAGO increased aggressive grooming in T20 winners, decreased hostile behavior (digging and throwing partner's litter) in T3 winners, and did not inflUence attacks in both groUps. It is sUggested that mu-opioid receptors are involved into forming the aggressive behavioral type in mice, and DAGO effects may be conditioned by emotional backgroUnd of these behavioral forms.     

Androgen‐metabolizing enzymes show region‐specific changes across the breeding season in the brain of a wild songbird

The Lapland longspur (Calcarius lapponicus) is an arctic‐breeding songbird that shows rapid behavioral changes during a short breeding season. Changes in plasma testosterone (T) in the spring are correlated with singing but not territorial aggression in males. Also, T treatment increases song but not aggression in this species. In contrast, in temperate‐zone breeders, song and aggression are highly correlated, and both increase after T treatment. We asked whether regional or temporal differences in androgen‐metabolizing enzymes in the longspur brain explain hormone‐behavior patterns in this species. We measured the activities of aromatase, 5α‐reductase and 5β‐reductase in free‐living longspur males. Aromatase and 5α‐reductase convert T into the active steroids 17β‐estradiol (E₂) and 5α‐dihydrotestosterone (5α‐DHT), respectively. 5β‐Reductase deactivates T via conversion to 5β‐DHT, an inactive steroid. We examined seven brain regions at three stages in the breeding season. Overall, aromatase activity was high in the hypothalamus, hippocampus, and ventromedial telencephalon (containing nucleus taeniae, the avian homologue to the amygdala). 5β‐Reductase activity was high throughout the telencephalon. Activities of all three enzymes changed over time in a region‐specific manner. In particular, aromatase activity in the rostral hypothalamus was decreased late in the breeding season, which may explain why T treatment at this time does not increase aggression. Changes in 5β‐reductase do not explain the effects of plasma T on aggressive behavior. © 1999 John Wiley & Sons, Inc. J Neurobiol 41: 176–188, 1999     

Serotonin and octopamine elicit stereotypical agonistic behaviors in the squat lobster Munida quadrispina (Anomura, Galatheidae)

Serotonin and octopamine have been implicated as modulators of posture and behavior in several crustaceans. Here we characterize the agonistic behaviors of normally interacting squat lobsters Munida quadrispina (Anomura, Galatheidae) and their responses to serotonin and octopamine injected into the ventral hemolymph sinus, in order to evaluate the potential roles of these amines in modulating agonistic behaviors. Normally interacting M. quadrispina do not develop lasting dominance hierarchies, although transient aggressive and submissive displays do occur. Injected serotonin elicits postures and behaviors in isolated individuals similar to those typical of aggressive, normally interacting animals. Injected octopamine can produce postures and behaviors typical of submissive animals, and elicits behaviors which imply a modulatory role for octopamine in tailflipping. The effects of both amines are reversible and dose dependent, and the dose-response curves parallel the normal progression of agonistic interactions. The social behaviors and reactions to injected serotonin and octopamine of M. quadrispina differ from those of lobsters and crayfish, indicating that interspecific differences in neuromodulation of behavior and motor output exist. Such differences have implications for the understanding of aminergic modulation of aggression and the evolution of aminergic modulation in crustaceans. Accepted: 22 June 1997     

The effects of castration and Silastic implants of testosterone on intermale aggression in the mouse

Castration and testosterone (T) replacement were used to study developmental changes in aggressive behavioral responsiveness to androgenic stimulation. Male mice castrated at birth were less sensitive to circulating T than were prepubertal or adult castrates, but fighting was induced in neonatal castrates with a dose of androgen that produced hypertrophy of the accessory organ system in adult castrates. Gonadectomy shortly prior to pubertal increases in serum T concentration also reduced behavioral responsiveness to androgen administration. Intermale aggression was induced in prepubertal castrates only with T treatment that maintained accessory organ growth in adult castrates. The aggressive behavior of males castrated after the pubertal surge in serum T was supported with circulating levels of androgen that failed to stimulate the accessory organ system above that of oil-treated castrates. It was concluded that T stimulation during neonatal or pubertal life is not totally crucial for organization of neural substrates that mediate the ultimate expression of intermale aggression, but exposure to androgen from birth throughout pubertal development is normally required to produce maximal aggressive behavioral responsiveness to circulating T encountered in adulthood.     

Case studies in antelope aggression control using a GnRH agonist

Maintaining surplus captive male antelope in bachelor groups can result in aggression in some species, leading to injury or death. Suppressing endogenous testosterone using gonadotropin‐releasing hormone (GnRH) analogs has been used in primates to control aggressive behavior, but little information is available on the use of GnRH analogs in nondomestic ruminant species. The aim of this study was to investigate the effect of a slow‐release GnRH agonist (deslorelin) on circulating hormone concentrations, semen and sperm characteristics and behavior in male gerenuk, dorcas gazelle, and scimitar horned oryx. Body weight, testicular volume, circulating hormone concentrations, ejaculate traits, and behavior were recorded before and during deslorelin treatment. A GnRH challenge (with serial blood sampling) was administered to gerenuk and dorcas gazelles before and during GnRH analog treatment. Quantitative behavioral data were collected for gerenuk and dorcas gazelles for 30 min three times a week, starting 1 month before deslorelin treatment, and the mean incidence of combined aggressive behaviors (supplanting, foreleg kicking, sparring, marking, and mounting) was compared before and during deslorelin treatment. No statistical difference (P>0.05) in body weight, semen volume, sperm concentration, percent sperm motility, percent sperm plasma membrane integrity, or percent normal sperm morphology was found before or during deslorelin treatment. The characteristic rise in luteinizing hormone (LH), occurring ～10 min following administration of a GnRH challenge in untreated males, was not evident during deslorelin treatment, although tonic LH concentrations were maintained. No differences (P>0.05) in the mean incidence of any aggressive behavioral traits in gerenuk or dorcas gazelle were detected before and during deslorelin. The absence of a GnRH‐induced increase in serum LH in treated males indicated that deslorelin suppressed pituitary responsiveness to endogenous GnRH, but that the continued tonic production of LH was sufficient to maintain testosterone production, aggressive behavior, and subsequent semen production. Zoo Biol 21:435–448, 2002. © 2002 Wiley‐Liss, Inc.     

Importance of cooperation and affiliation in the evolution of primate sociality

The idea that competition and aggression are central to an understanding of the origins of group‐living and sociality among human and nonhuman primates is the dominant theory in primatology today. Using this paradigm, researchers have focused their attention on competitive and aggressive behaviors, and have tended to overlook the importance of cooperative and affiliative behaviors. However, cooperative and affiliative behaviors are considerably more common than agonistic behaviors in all primate species. The current paradigm often fails to explain the context, function, and social tactics underlying affiliative and agonistic behavior. Here, we present data on a basic question of primate sociality: how much time do diurnal, group‐living primates spend in social behavior, and how much of this time is affiliative and agonistic? These data are derived from a survey of 81 studies, including 28 genera and 60 species. We find that group‐living prosimians, New World monkeys, Old World monkeys, and apes usually devote less than 10% of their activity budget to active social interactions. Further, rates of agonistic behaviors are extremely low, normally less than 1% of the activity budget. If the cost to the actors of affiliative behavior is low even if the rewards are low or extremely variable, we should expect affiliation and cooperation to be frequent. This is especially true under conditions in which individuals benefit from the collective environment of living in stable social groups. Am J Phys Anthropol 128:84–97, 2005. © 2005 Wiley‐Liss, Inc.     

Affiliative and Aggressive Behavior in a Group of Female Somali Wild Ass (Equus africanus somalicus)

We observed a group of three young female Somali wild asses to develop an ethogram of social behavior in the first phase of a longer term study of social, sexual, and maternal/infant behavior. The most unexpected finding was the frequency and extent of aggressive interactions, which included Charge, Drive, Neck Wrestle, Head Butt, and Body Slam, behaviors previously reported only for males of other equid species. The overall frequency of aggressive behavior was higher than that of affiliative behavior (84±16.5 vs. 32±5.5, P=0.03), yet no injuries occurred. The dyadic directionality of aggressive behavior suggested a dominance hierarchy, a feature not previously reported for either wild ass or domestic donkeys. The aggression observed may be an accurate representation of the behavior of this species, or their relatively young ages, or their recent transfer from their natal group through quarantine and into a new enclosure may have heightened agonistic tendencies. Further studies will determine whether with time their aggressive behavior becomes more intense or dissipates with maturity. Zoo Biol 31:87;–97, 2012. © 2011 Wiley Periodicals, Inc.     

Extensive Reorganization of Behavior Accompanies Ontogeny of Aggression in Male Flesh Flies

Aggression, costly in both time and energy, is often expressed by male animals in defense of valuable resources such as food or potential mates. Here we present a new insect model system for the study of aggression, the male flesh fly Sarcophaga crassipalpis, and ask whether there is an ontogeny of aggression that coincides with reproductive maturity. After establishing that reproductive maturity occurs by day 3 of age (post-eclosion), we examined the behavior of socially isolated males from different age cohorts (days 1, 2, 3, 4, and 6) upon introduction, in a test arena, with another male of the same age. The results show a pronounced development of aggression with age. The change from relative indifference to heightened aggression involves a profound increase in the frequency of high-intensity aggressive behaviors between days 1 and 3. Also noteworthy is an abrupt increase in the number of statistically significant transitions involving these full-contact agonistic behaviors on day 2. This elevated activity is trimmed back somewhat by day 3 and appears to maintain a stable plateau thereafter. No convincing evidence was found for escalation of aggression nor the establishment of a dominance relationship over the duration of the encounters. Despite the fact that aggressive interactions are brief, lasting only a few seconds, a major reorganization in the relative proportions of four major non-aggressive behaviors (accounting for at least 96% of the total observation time for each age cohort) accompanies the switch from low to high aggression. A series of control experiments, with single flies in the test arenas, indicates that these changes occur in the absence of the performance of aggressive behaviors. This parallel ontogeny of aggressive and non-aggressive behaviors has implications for understanding how the entire behavioral repertoire may be organized and reorganized to accommodate the needs of the organism.     

Neurological effects of aromatase deficiency in the mouse

In the brain, the conversion from androgen into estrogen is an important process for the differentiation of the brain function in male rodents. The aromatase is expressed in some nucleus of the brain. To assess the functional significance of the aromatase gene in development and activation of sex-specific behavior, we analyzed behavioral phenotypes of the aromatase knockout (ArKO) male mice. ArKO males obviously decreased their fertility and showed deficits in male sexual behavior including mount, intromission and ejaculation. Noncontact penile erection was not significantly affected by defect of the aromatase gene. A reduction of aggressive behavior against male intruders was also observed in ArKO males, while they tend to exhibit aggression toward estrous females during male copulatory tests. Moreover, the infanticide toward the pups was observed in the ArKO males, whereas characteristic parental behavior, but not infanticide was observed in wild-type males. These results indicate that aromatase gene expression is a critical step not only for motivational and consummatory aspects of male sexual behavior, but also for aggressive and parental behaviors in male mice.     

Increased aggression and activity level in 3- to 11-year-old girls with congenital adrenal hyperplasia (CAH)

Experimental research in a wide range of mammals has documented powerful influences of androgen during early development on brain systems and behaviors that show sex differences. Clinical research in humans suggests similar influences of early androgen concentrations on some behaviors, including childhood play behavior and adult sexual orientation. However, findings have been inconsistent for some other behaviors that show sex differences, including aggression and activity level in children. This inconsistency may reflect small sample sizes and assessment limitations. In the present study, we assessed aggression and activity level in 3- to 11-year-old children with CAH (38 girls, 29 boys) and in their unaffected siblings (25 girls, 21 boys) using a questionnaire that mothers completed to indicate current aggressive behavior and activity level in their children. Data supported the hypotheses that: (1) unaffected boys are more aggressive and active than unaffected girls; (2) girls with CAH are more aggressive and active than their unaffected sisters; and (3) boys with and without CAH are similar to one another in aggression and activity level. These data suggest that early androgens have a masculinizing effect on both aggressive behavior and activity level in girls.     

Social parameters and urinary testosterone level in male chimpanzees (Pan troglodytes)

Studies investigating relationships between social parameters (such as dominance rank, rates of aggressive and sexual behaviors) and androgen (particularly, testosterone) levels in male primates have yielded inconsistent results. In the present study, we address the relationship between androgens, male dominance rank and rank-associated behaviors in two groups of captive chimpanzees, a species characterized by a pronounced dominance hierarchy between adult males. By combining behavioral observations with urinary testosterone (T) measurements, we found that the differences in T concentrations between males were small and not obviously related to their dominance rank. T levels were not related to the rates of initiated aggression and copulatory behavior, but a significant negative relationship between male T level and the rates of strong aggression received was apparent. Our findings, combined with those of others, suggest that any relationship between dominance rank and T depends upon the extent to which individual rank-associated behaviors (e.g. aggressive/sexual) are themselves related to T.