Search

Research has indicated that men's facial width-to-height ratio (fWHR) is part of an evolved system of social dominance, aggression, and power. fWHR has been linked to antisocial behavior, measured by self-reported aggression, but recent studies have failed to replicate this finding. To overcome these inconsistencies, influencing factors such as social status have to be taken into account in order to explain the relationship between fWHR and aggression. In particular, income has been shown to be an important influencing factor in this relationship. Furthermore, previous findings suggested that testosterone is linked to fWHR and might be associated with fWHR and dominance-related outcomes. Therefore, this study examined the influence of both social status defined by income and salivary testosterone on the association between fWHR and self-reported dominance-related behavioral traits. In particular, links between fWHR and self-report measures of aggression and the Dark Triad (encompassing psychopathy, Machiavellianism, and narcissism) were investigated in N = 109 men aged 40 to 75 years. fWHR was significantly associated with physical aggression and two of the Dark Triad traits (psychopathy and Machiavellianism) in men reporting low income. The relationship between fWHR and narcissism was moderated by testosterone. The findings highlight the importance of considering social status and neuroendocrine parameters such as testosterone when examining associations between fWHR and complex psychological traits and behaviors. [ABSTRACT FROM AUTHOR]

In gregarious animals, social interactions frequently take the form of dominance hierarchies that maintain stable relationships between individuals, and settle disputes without extra costs. Traits that function as signals of status can play an important role in mediating interactions among individuals, both in social and in sexual contexts. Carotenoid ornaments are more generally assumed to be sexually selected and not so relevant to general social contexts. However, it is possible for them to function in social contexts if they signal socially relevant aspects. Here we experimentally analysed social dominance and resource control in male groups of a gregarious species, the European serin, Serinus serinus , in relation to a sexual ornament. We tested whether yellow carotenoid-based plumage coloration, age, body size and testosterone were predictors of social dominance over a nonsexual resource (i.e. feeding context). We showed that dominance hierarchies were steep and were related to testosterone levels and ornamental coloration, particularly the male yellow carotenoid-based crown patch. Our results suggest that carotenoid-based colour and testosterone levels can be reliable predictors of social status in agonistic encounters in groups of male serins. Moreover, together with previous work on the sexual function of male coloration, this study provides evidence that male serin yellow coloration has a dual function in both sexual and nonsexual contexts. These results raise the possibility that this ornament may have evolved and be maintained via social selection over social competition/cooperation for reproductive opportunities and ecological resources. [ABSTRACT FROM AUTHOR]

In social mammals, the position of a male in the group’s hierarchy strongly affects his reproductive success. Since a high social rank is often gained through competition with other males, selection should favour bigger males over smaller ones. We may therefore predict faster growth and/or delayed sexual maturity in dominant males. Likewise, dominants should have higher levels of testosterone, hormone important in many aspects of male dominance. Less obvious is the relationship between dominance and levels of corticosterone but generally higher concentrations are expected in subordinate individuals. We studied body growth, sexual maturation and endocrinal changes in males of two house mouse subspecies, raised in fraternal pairs. Since Mus musculus domesticus is the subspecies which dominates mutual encounters with Mus musculus musculus we predicted higher growth rate, delayed puberty and aggression, and higher testosterone and corticosterone levels in domesticus males compared to musculus . In all comparisons, no differences were found between dominant and subordinate musculus brothers. On the other hand, in M. m. domesticus , dominant males revealed a different growth trajectory and lower corticosterone levels than subordinate males but not delayed puberty and higher testosterone concentrations, thus contradicting our predictions. In inter-subspecific comparisons, musculus males matured earlier but became aggressive at the same time as domesticus males. The musculus testosterone ontogeny suggests that social positions in this subspecies remain unfixed for an extended period and that the increasing levels probably reflect prolonged hierarchy contests. It appears that the ontogeny of behaviour and physiological traits diverge cryptically between the two subspecies. [ABSTRACT FROM AUTHOR]

Highlights: [•] The mechanisms underlying yolk testosterone-mediated maternal effects are unclear. [•] A testosterone implant increased dominance, song activity and song consistency. [•] This effect did not depend on the embryonic exposure to yolk testosterone. [•] Thus elevated yolk testosterone levels did not alter the testosterone sensitivity. [•] Further research is urgently needed to identify the underlying mechanism(s). [Copyright &y& Elsevier]

Dimorphism on dominance and agonistic behaviour in mammals tends to be strongly biased toward males. In this review, we focus on a select few species of mammals in which females are as or more aggressive than males, and/or are dominant to males, and explore the role of androgenic hormones in mediating this important difference. While the data are not as clear-cut as those published on traditional laboratory mammals, our review highlights important endocrine substrates for both organizational and activational influences of steroids on female aggressive behaviour. We highlight areas in which further observations and experiments are crucial, especially the potential facilitative effects of androgens on female aggression. Finally, new and innovative techniques, including molecular genetics and receptor pharmacology, portend important insights into the ways in which androgenic hormones regulate aggressive behaviour in 'atypical' female mammals. [ABSTRACT FROM AUTHOR]

Abstract: Among vertebrates, winning a fight enhances the probability of future victories and vice versa and the role of post-conflict testosterone in mediating this ‘winner effect’ is widely accepted. In a series of staged fights of Japanese quail (Coturnix japonica) we tested both opponents' pre-fight and post-conflict testosterone, behavior and dominance status after returning to their social groups. We found that the presence of a familiar mixed-sex audience during the encounter modulated both the testosterone response and the long‐term success after a fighting experience. ‘Public losers’ but not ‘public winners’ lacked a post-conflict testosterone response, whereas without an audience both winners and losers increased testosterone metabolite levels. Long-lasting winner and loser effects exclusively occurred when the performance information was perceived by a mixed-sex audience. In further experiments we manipulated the testosterone responsiveness of either the loser or the winner. An artificial post-conflict testosterone surge after having lost a fight effectively reversed the loser effect in Japanese quail. In contrast, the ‘winner effect’ was not changed by blocking testosterone after the fight. Overall, male Japanese quails' post-conflict testosterone was connected to the audiences and thus, own or the observers' perception of the challenge rather than to winning or losing a fight. [Copyright &y& Elsevier]

Abstract: Prenatal testosterone exposure has been suggested to influence various personality traits including assertiveness/social dominance, aggressiveness, and impulsive sensation seeking (ImpSS). However, correlational work using 2D:4D digit ratio as an indicator for prenatal testosterone only converged on extremely small effects. Here we show that measuring traits with a high degree of specificity by combining extensive personality assessment, factor analysis with oblique rotation and subsequent partialling reveals an association between ImpSS and low 2D:4D (i.e. presumably high prenatal testosterone) in young healthy males. These findings suggest that prenatal testosterone exposure predicts ImpSS in men, that 2D:4D-personality associations are more specific than generally appreciated and that such associations can be more reliably detected using the approach to trait assessment described here. [Copyright &y& Elsevier]

Hormones seem to play important roles in the regulation of human aggression. Multiple studies have confirmed that testosterone (T) levels exhibit complex relationships with aggression, dominance, and/or risk-taking behavior. Some evidence suggests that cortisol (CORT) interacts with T and may also be associated with aspects of mood and aggression. However, almost no research to date has investigated the possibility that these neuroendocrine factors are associated with variations in political attitudes or with political aggression. During the second intifada, we tested the hypothesis that morning salivary T and/or salivary CORT levels might be associated with self-rated aggression or with support for religio-political aggression (RPA) among 14-year-old Palestinian boys living in Gaza. We obtained and averaged weekly 09:00 hr salivary measures of T and CORT for more than 1 month. Averaged morning T levels did not correlate with self-rated aggression, but were positively associated with agreement with the statement 'religious ends justify any means,' ( r = .355, P = .014) and marginally associated with a composite measure of support for RPA ( r = .247, P = .094). Average CORT levels were inversely correlated with self-rated aggression ( r = −.328, P = .037) and with anger ( r = −.373, P = .016), but CORT levels were not associated with support for RPA or with the statement 'religious ends justify any means.' Acknowledging that a modest sample size and methodological issues necessarily limit confidence in our conclusions, these results may represent the first findings regarding neurobiological correlates of support for political aggression. Aggr. Behav. 37:121-132, 2011. © 2010 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

Handgrip strength (HGS) is highly heritable and a good overall measure of strength and muscle function. Indicative of blood testosterone levels and fat-free body mass, HGS is also highly sexually dimorphic. Recent psychological research shows that HGS is correlated with a number of social variables, but only in males. We conducted three studies to further investigate the relationship between HGS and measures of aggression and social competition among adolescents. Consistent with previous reports, correlations were almost exclusive to males, but this was only visible during late adolescence (i.e., high school). These findings support evolutionary hypotheses regarding grip strength in male-male competition and suggest that similar to measures of testosterone, HGS is a measure that is predictive of social behavior in older adolescent males. [ABSTRACT FROM AUTHOR]

Abstract: Attempts to link testosterone to dominance dispositions using self-report measures of dominance have yielded inconsistent findings. Similarly, attempts to link testosterone changes to a situational outcome like winning or losing a dominance contest have yielded inconsistent findings. However, research has consistently shown that an indirect measure of an individual’s dominance disposition, implicit power motivation, is positively related to baseline testosterone levels and, in interaction with situational outcomes, predicts testosterone changes. We propose a hormonal model of implicit power motivation that describes how testosterone levels change as an interactive function of individuals’ implicit power motivation and dominance situations. We also propose that estradiol, and not testosterone, plays a key role in dominance motivation in women. [Copyright &y& Elsevier]

Aggression is a fundamental behavior displayed universally among animal species, but hyper- or hypo-aggressiveness can be maladaptive with negative consequences for individuals and group members. While the social and ecological significance of aggression is well understood, the specific neurobiological and hormonal mechanisms responsible for mediating aggression have not been fully elucidated. Previous studies have shown a relationship between aggressive acts and circulating gonadal steroids, but whether classical nuclear steroid receptors regulate aggression in animals is still uncertain. We examined whether the nuclear androgen receptor (Ar) and nuclear progestin receptor (Pgr) were necessary for aggressive behaviors and maintenance of a dominance relationship in male zebrafish (Danio rerio). Dyadic social interactions of Ar knockout (ArKO), Pgr knockout (PgrKO) and wildtype (WT) controls were observed for two weeks (2-weeks). ArKO zebrafish were significantly less aggressive and had a less defined dominance relationship, whereas PgrKO dominant zebrafish were significantly and persistently more aggressive with a robust dominance relationship. Our results demonstrate the importance of nuclear steroid hormone receptors in regulating aggression of adult male zebrafish and provide new models for understanding of the mechanisms of aggression. • Androgen receptor (Ar) and progestin receptor (Pgr) inversely regulate aggression. • ArKO were less aggressive and had a less defined dominance relationship. • PgrKO were more aggressive and had a robust dominance relationship. [ABSTRACT FROM AUTHOR]

Group living confers many benefits while simultaneously exposing group members to intense competition. An individual's rise to prominence within a group may conflict with the overall functioning of the group. There is therefore a complex and dynamic relationship between the behavioral displays that directly benefit an individual, the consequences of these actions for the community, and how they feed back on individual-level fitness. We used a network analysis approach to study the link between behavior, social stability, and steroid hormone levels in replicate communities of the cichlid fish, Astatotilapia burtoni, which live in social groups with a dominance hierarchy. We demonstrate that individual behavior can have direct and indirect effects on the behavior of others while also affecting group characteristics. Our results show that A. burtoni males form stable social networks, where dominant individuals act as hubs for social interactions. However, there was variation in the temporal stability in these networks, and this variation in stability impacted hormone levels. Dominant males had higher testosterone levels, however, the differences in testosterone levels between dominant and subordinate males were greatest in stable communities. In sum, our analyses provide novel insights into the processes by which individual and community properties interact. • Group living confers benefits while exposing group members to competition. • Social network analysis is used to study naturalistic communities of a cichlid fish. • Community membership is predictive of both testosterone and cortisol levels. • Variance in testosterone levels depends on group stability. [ABSTRACT FROM AUTHOR]

A novel 'field' study recently published in Aggressive Behavior found that individual differences in baseline testosterone concentrations were positively correlated with endorsement of political aggression and that baseline cortisol concentrations were negatively correlated with self-reported aggression among Palestinian boys living in Gaza. Here, we discuss recent evidence indicating that testosterone and cortisol interact to predict competitive, aggressive, and dominant behaviors and urge researchers collecting both hormones to perform and report analyses that formally test for such interaction effects. Aggr. Behav. 37:489-491, 2011. © 2011 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

The role of androgens in shaping "masculine" traits in males is a core focus in behavioral endocrinology, but relatively little is known about an androgenic role in female aggression and social dominance. In mammalian models of female dominance, including the ring-tailed lemur (Lemur catta), links to androgens in adulthood are variable. We studied the development of ring-tailed lemurs to address the behavioral basis and ontogenetic mechanisms of female dominance. We measured behavior and serum androgen concentrations in 24 lemurs (8 males, 16 females) from infancy to early adulthood, and assessed their 'prenatal' androgen milieu using serum samples obtained from their mothers during gestation. Because logistical constraints limited the frequency of infant blood sampling, we accounted for asynchrony between behavioral and postnatal hormone measurements via imputation procedures. Imputation was unnecessary for prenatal hormone measurements. The typical sex difference in androgen concentrations in young lemurs was consistent with adult conspecifics and most other mammals; however, we found no significant sex differences in rough-and-tumble play. Female (but not male) aggression increased beginning at approximately 15 months, coincident with female puberty. In our analyses relating sexually differentiated behavior to androgens, we found no relationship with activational hormones, but several significant relationships with organizational hormones. Notably, associations of prenatal androstenedione and testosterone with behavior were differentiated, both by offspring sex and by type of behavior within offspring sexes. We discuss the importance of considering (1) missing data in behavioral endocrinology research, and (2) organizational androgens other than testosterone in studies of female dominance. • Androgens may influence female aggression and dominance. • Across species, links between androgens and female dominance are variable. • We collected longitudinal data on juvenile Lemur catta and their mothers. • Despite typical androgenic sex differences, female aggression rises during development. • Maternal androgens predict offspring play and aggression. [ABSTRACT FROM AUTHOR]