Subordinate Males Research Articles

The context of sexual coercion in orang-utans: when do male and female mating interests collide?

Sexual coercion is widespread in the animal kingdom. Its direct forms, including harassment and forced copulation, have largely been investigated as an expression of (alternative) male reproductive strategies, rather than the result of a sexual conflict between the sexes. Likewise, the frequent occurrence of forced copulations in orang-utans (Pongo spp.) has been attributed to male strategies and more recently also to concealed female fecundity. So far, however, the immediate contextual variables leading to forced copulations have rarely been examined. We compared two orang-utan populations, Suaq (Pongo abelii, Sumatra) and Tuanan (Pongo pygmaeus, Borneo), both characterized by an individual-based fission–fusion lifestyle, whereas their socioecology differs. We assessed how the occurrence of female-resisted and voluntary copulations was affected by female reproductive state, male morph (unflanged or flanged), measures of male–male competition, male–female relationship and ecological factors. Besides female reproductive state and male morph, predictors of female resistance were related to male–male competition. First, female resistance was more likely towards subordinate males who were displaced from proximity to the female by another male during that association. Second, the presence of additional flanged males increased the probability of female resistance. Third, the latency to both the arrival of another male and to the end of the association after sexual interactions was shorter if there was female resistance. We conclude that sexual coercion in orang-utans is highly dependent on the vicinity of more dominant males and can only be understood in the light of sexual conflict: While males force copulations when at risk of losing access to a female and thus follow a ‘now-or-never’ strategy, female resistance follows a ‘not-you-now’ pattern, which is ultimately consistent with an infanticide avoidance strategy.

Gene expression pattern of Kisspeptin and RFamide-related peptide (Rfrp) in the male Damaraland mole-rat hypothalamus

Damaraland mole-rats (Fukomys damarensis) are cooperatively breeding, subterranean mammals, which exhibit high reproductive skew. Reproduction is monopolized by the dominant female of the group, while subordinates are anovulatory. Similarly, male subordinates within the colony show no sexual behaviour although they have functional gonads and do not differ from reproductive males in circulating levels of pituitary hormones and testosterone. However, reproductive status affects the neuroendocrine phenotype of males with breeders possessing increased mRNA expression of androgen and progesterone receptors compared to non-breeders in several forebrain regions implicated in the regulation of reproductive behaviour. The RFamide peptides kisspeptin and RFRP-3, encoded by the Kiss1 and Rfrp gene, are considered potent regulators of gonadotropin release. In females, reproductive inhibition is associated with reduced Kiss1 expression within the arcuate nucleus (ARC) and increased Rfrp expression in the anterior hypothalamus. To assess whether differential gene expression of Kiss1 and Rfrp underlies the difference in reproductive behaviour of males, we studied the expression of both genes by means of in situ hybridisation in wild-caught male Damaraland mole-rats with different reproductive status. The distribution of Kiss1 and Rfrp within the hypothalamus was found to be similar to females. Quantification of the Kiss1 hybridisation signal revealed no significant differences in relation to reproductive status. However, there was a significant positive correlation between testis mass and the number of Kiss1-expressing cells in the ARC and the mRNA content per cell, respectively. Analysis of the Rfrp hybridisation signal along the rostro-caudal extent of the hypothalamus revealed that non-reproductive males possessed an increased number of Rfrp-expressing cells at the level of the dorsomedial hypothalamic nucleus (DMH) than reproductive males. These data suggest the Kiss1 expression within the ARC is not associated with reproductive quiescence in subordinate males but instead, inhibitory effects may be mediated by Rfrp-expressing cells in the DMH.

Social instability influences rank-specific patterns of oxidative stress in a cichlid fish.

In many animal societies, dominant individuals have priority access to resources. However, defending high rank can be costly, especially in unstable social hierarchies where there is more intense competition. Oxidative stress has been proposed as a potential cost of social dominance, but few studies have examined this cost in relation to social stability. We studied the cost of social dominance in the cichlid fish Astatotilapia burtoni by manipulating social stability among males in replicate naturalistic communities for 22 weeks. We found that our social stability treatment influenced status-specific patterns in 3 out of 6 measurements of oxidative stress. Specifically, dominant males experienced increased plasma oxidative damage (measured as reactive oxygen metabolites, ROMs) compared with subordinate males in stable hierarchies only. Subordinate males in unstable hierarchies had higher ROMs than their stable community counterparts, but we found no effect of social stability treatment for dominant males. However, dominant males tended to have reduced total antioxidant capacity (TAC) in the liver when compared with subordinate males in unstable hierarchies, suggesting that the cost of social dominance is higher in unstable hierarchies. There were no effects of status and treatment on gonad TAC, muscle TAC or oxidative DNA damage. We conclude that the stability of the social environment influences the relative cost of social dominance in a tissue- and marker-specific manner.

Social dominance does not increase oxidative stress in a female dominance hierarchy of an African cichlid fish

AbstractIn many group living animal species, individuals use aggression to gain and maintain social dominance to secure access to ecological resources and potential mates. While social dominance has many fitness benefits, there are also potential costs associated with frequent agonistic interactions and status display. One potential cost of social dominance is oxidative stress, the imbalance of reactive oxygen species and antioxidant capacity. In the cichlid species Astatotilapia burtoni, dominant males are aggressive, hold a breeding territory, and have an activated reproductive system resulting in larger gonads. Subordinate males are submissive, school with females, and are nonreproductive. Females are submissive under natural conditions, but in a female‐only group, a dominance hierarchy will form with dominant females taking on male‐typical behaviours including aggression, territory defence, and increased androgen levels. However, in contrast to males, social dominance is not linked to increased activation of the reproductive system in females, allowing us to test whether social dominance alone exposes individuals to increased oxidative stress. We compared dominant and subordinate females in female‐only groups in five markers of oxidative stress. Dominant females did not have higher levels of oxidative damage compared to same‐sex subordinates. This result contrasted to the trend in males in which dominant males had higher oxidative damage than their subordinate counterparts. Our findings suggest that the oxidative cost of social dominance is limited and support the notion that previously reported associations between high rank and increased oxidative stress is most likely driven by increased investment in reproduction.

Female choice and male aggression in the polymorphic lizard Sceloporus minor

AbstractIn comparison with some other vertebrate groups, female choice in lizards is relatively poorly understood. In contrast, aggressive behavior in lizards has been better studied; nevertheless, there are many genera and even whole families for which little or no information on aggressive behavior has been described. Therefore, the objective of this study was to experimentally evaluate the importance of morphometric traits, body coloration, and behavioral attributes of male Sceloporus minor from a population in central Mexico in order to (1) determine whether female choice exists in this species, and if so, identify which features of males females are using to do so, and (2) identify the phenotypic features of males that predict dominance status in contests between dominant and subordinate males. We found that females of S. minor indeed show a preference for males on the basis of ventral patch color; specifically, females chose males with ventral patches of Spectrum Blue or True Blue over males with ventral patches of other blue hues, but found no evidence of choice based on other morphological characters examined. Results also showed that winner (i.e., dominant) males exhibited more aggressive behaviors and were larger in body size than subordinate (i.e., loser) males. Notably, we found no support for a role of male polymorphic dorsal coloration on either female choice or male contest outcome. The results of this study showed evidence of female choice and male‐male competition, suggesting that in this population, males exhibit intrasexual interactions to compete for resources such as territories and produce displays that serve in part to attract females.

The Female Beehive: How Queen Bee Behavior Affects Female Subordinates’ Career-Related Outcomes

Past work has found that female leaders in male-dominated environments often experience threats to their identities that they manage by engaging in individual mobility strategies (i.e., disassociating themselves from their gender identity; the Queen Bee phenomenon). This research explores the impact of this behavior on subordinates. We argue that Queen Bee behaviors cause female subordinates to feel uncertain about whether they belong in their organizations, which in turn, causes them to differentiate themselves from female leaders, reduce leadership aspirations, and increase turnover intentions. We develop our predictions through an inductive study of interviews with female employees and then test these predictions through two experimental studies (i.e., Cyberball, vignettes). We find support for our predictions for female subordinates whereas we find that irrespective of whether female leader engages in Queen Bee behavior or not, male subordinates’ sense of belonging, differentiation, leadership aspirations, and turnover intentions do not differ.

Social bonds provide multiple pathways to reproductive success in wild male chimpanzees

SummaryIn most male mammals, fitness is strongly shaped by competitive access to mates, a non-shareable resource. How, then, did selection favor the evolution of cooperative social bonds? We used behavioral and genetic data on wild chimpanzees (Pan troglodytes schweinfurthii) in Gombe National Park, Tanzania, to study the mechanisms by which male-male social bonds increase reproductive success. Social bonds increased fitness in several ways: first, subordinate males that formed strong bonds with the alpha male had higher siring success. Independently, males with larger networks of strong bonds had higher siring success. In the short term, bonds predicted coalition formation and centrality in the coalition network, suggesting that males benefit from being potential allies to numerous male rivals. In the long term, male ties influenced fitness via improved dominance rank for males that attain alpha status. Together, these results suggest that male bonds evolved in chimpanzees by affording both short- and long-term pathways to reproductive success.

Dominant males exploit the courtship effort of subordinate males in an Amazonian fish

Reproductive behaviour is often targeted by behavioural parasitism due to its high energy costs and direct relationship with fitness. Courtship behaviour represents a substantial amount of the investment in reproduction, as it usually requires conspicuous movements that are energetically demanding and increase predation risk. Here, we present an alternative reproductive tactic in which dominant male sailfin tetra, Crenuchus spilurus Günther 1863, parasitize the courtship behaviour of subordinate males. By conducting field observations and controlled experiments in laboratory, we show that, under low availability of nesting sites, dominant males favour a close-range defence of nesting sites, while subordinate males invest more in courtship activities. However, subordinate males often directed courtship movements towards a nesting site dominated by a concealed dominant male, who subsequently took over the female and resumed courtship. Our laboratory experiment also showed that only dominant males obtained spawning success regardless of the amount of effort allocated to courtship behaviour, circumventing the initial female preference for the subordinate male. Subordinate males were more likely to initiate contests and ceased courtship upon losing aggressive contests. In such instances, the courtship effort of dominant males was higher, suggesting that dominant males modulate their courtship effort according to the effort of subordinate males. We refer to this tactic as courtship piracy. For being dependent on resource defence, the effectiveness of courtship piracy is contingent on the defendability of nesting sites. In a follow-up experiment, we show that dominant males invest more in nesting site defence only when nesting sites are scarce. Since rainfall controls the amount of nesting sites in the natural habitat, we suggest that seasonality modulates the relative contribution of courtship piracy and female mate choice to reproductive success. • Dominant males defend nesting sites, while subordinate males engage in courtship. • Only dominant males obtained spawning success, regardless of effort in courtship. • Dominant males parasitize the courtship behaviour of subordinate males. • Effectiveness of courtship piracy depends on the defendability of nesting sites. • Seasonality may control the contribution of courtship piracy to reproductive success.

Tactical deception in sociosexual behaviour of stump-tailed macaques (Macaca arctoides): an exploratory study

Abstract Tactical deception (TD) is a social strategy in which a subject performs an action to its own benefit causing disadvantage for a competitor. In primates, the cognitive mechanisms involved in TD have been described at different levels. Sneaky mating is a common context within which to study TD because in many primate groups, dominant males monopolize access to females and subordinate males must find a way to copulate with females avoiding the alpha’s presence. The objective of this study was to explore which of the TD behavioural strategies are involved in the male sociosexual behaviour of a group of stump-tailed macaques (Macaca arctoides). We found that the subordinate males participated in more interactions when they were in a section of the enclosure where the alpha male was not present. The alpha male had more copulation interactions, but the beta male’s interactions lasted longer on average. Our data offer evidence in support of the hypothesis that stump-tailed macaques may use TD strategies that are related to operant conditioning.

Third-party assessment of contestants during fallow deer fights increases with resource abundance and dominance rank

The decision to engage in escalated fighting involves an interplay between the individual's estimate of the value of the resource under dispute and the ability of the combatants to invest sufficient time and energy in the contest. Although fallow deer, Dama dama , contests usually take place between pairs of individuals, they are sometimes terminated by the intervention of dominant third-party individuals. Theory argues that these interventions prevent subordinates from gaining a competitive boost via a winner effect; thus, interveners benefit by removing this threat to their status. Prior to intervention, third-party individuals often approach and closely follow the competing dyad before either abandoning their interest in the contest, or physically targeting one of the contestants. This study investigated the possibility that third-party following is an assessment process whereby individuals monitor the quality of fighting rivals during the annual rut. We tested three hypotheses: (1) that third-party followers are socially dominant individuals, that (2) follow contests to assess the current quality of high-ranking rivals (3) when resource abundance (i.e. the number of oestrous females) is high. Our results show that socially dominant individuals are most likely to follow contests; however, contrary to expectation, third-party males tended to follow dyads consisting of low-ranking rivals. We also show that as resource abundance increased in the population there was an increased tendency for males to follow contests, and a reduction in the probability of engaging in a third-party intervention of the contest. As expected by theory, dominance and resource abundance were important correlates of third-party following. Our results support the idea that socially dominant males monitor subordinate males that possess sufficient resources to expend in fighting, and that thus may be a threat to their status. • Dyadic contests are frequently followed by third-party males. • Following increases as the number of oestrous females increases. • Third-party individuals tend to follow dyads with low-ranking rivals. • Following contests facilitates assessment of rivals when resources are available.

Social network dynamics predict hormone levels and behavior in a highly social cichlid fish

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.

Transcriptome of Distinct LH and FSH Cells Reveals Different Regulation Unique to Each Cell Type

From mammals to fish, gametogenesis and sexual maturation are driven by LH and FSH, the two gonadotropic hormones temporally secreted from the pituitary. Teleost fish are an excellent model for addressing the unique regulation and function of each gonadotropin hormone since, unlike mammals; they synthesize and secrete LH and FSH from distinct cells. By performing cell specific transcriptome analysis of double-labelled transgenic Nile tilapia (Oreochromis niloticus) expressing GFP and RFP in LH or FSH cells, respectively, we identified genes specifically enriched in each cell type. Though GnRH is considered the main neuropeptide regulating LH and FSH, we found that each LH and FSH cell express unique GPCR signature that reveals the direct regulation of additional metabolic and homeostatic hormones (like cholecystokinin, somatostatin and glutamate). Moreover, some of those GPCRs were conserved also in gonadotrophs of mammals (like PACAP receptor, Adropin receptor and GABBA receptor). Next, we had exploited the unique behavior of Nile tilapia where a behavioral hierarchy is created between males, to compare the gene expression in the pituitary and brain of dominant (reproducing) males to a subordinate (non-reproducing) males. By combining the two transcriptome sets we had identified novel players in the hypothalamic regulation of the HPG axis, and revealed how brain aromatase (cyp19a1b), that is enriched specifically in LH cells, is the key factor in regulating the activity of LH and FSH cells in dominant reproducing fish. Thereby, unraveling novel mechanisms in the differential regulation of LH and FSH. The research was funded by the Israel Science Foundation (ISF) no. 1540/17.

Social Rank, Behavioral Phenotypes and Kappa Opioid Receptor: PET Imaging Studies of Socially Housed Female and Male Monkey Models of Cocaine Use Disorder

In the US, cocaine use is increasing, alongside cocaine overdose deaths, which doubled from 2014 to 2016 (Nolan et al., J Urban Health 2019; John and Wu, Drug Alcohol Depend 2017). While dopamine (DA) has been implicated in the positive reinforcing effects of drugs, the kappa opioid receptor (KOR) system and its endogenous ligand, dynorphin, are implicated in the neurobiological regulation of aversive states, including stress associated with substance abuse. Both chronic stress and cocaine exposure increase dynorphin/KOR system function and sensitivity to stress-induced relapse (Tejeda and Bonci, Brain Research 2019). A recent positron emission tomography (PET) study with KOR agonist tracer [11C]EKAP, in humans, reported an inverse correlation between social status and KOR availability in “anti-reward”/stress brain regions (Matuskey et al. Neuropsychopharmacology 2019). Differences in KOR availability have also been shown to correlate with cocaine choice in subjects with CUD (Martinez et al. Neuropsychopharmacology 2019). The aim of this study is to extend the investigation of the dynorphin/KOR system using a homologous nonhuman primate model of CUD involving cocaine self-administration, primate social behavior, and PET imaging. The ongoing study utilizes cocaine-naïve male and female monkeys (N=8/sex) living in same-sex social groups of 4/pen. The first aim was to investigate the KOR system, combining [11C]EKAP PET imaging and primate social behavior to assess the relationship between social rank and KOR availability. The second aim was to extend our research to include measures of impulsivity using a delayed discounting procedure. Monkeys were trained under a 1- vs. 3-food pellets delay discounting choice procedure. The primary dependent variable was indifference point (IP), or the delay that results in 50% choice for both reinforcers. In PET studies, the lowest binding potentials (BPs) across all regions of interest were observed in dominant (Dom) females and subordinate (Sub) males; the two most vulnerable phenotypes to cocaine reinforcement (Morgan et al., Nature Neurosci 2002; Nader et al., Biol Psych 2012). We hypothesize this was due to increased basal dynorphin levels, indicative of chronic social stress. Studies are currently underway to assess cocaine acquisition. We hypothesis Dom females and Sub males, those with lower KOR BPs will acquire cocaine reinforcement at lower doses compared to Dom males and Sub females. In delay discounting studies, the IP values ranged from 23-107 seconds (Mdn = 38). Preliminary data indicates no sex or social rank differences in IP values. However, redetermining the delay discounting curve resulted in significantly higher IP values, which were correlated with BP in several brain regions in males but not females. The redetermined IP values may provide an index of adaptability; we speculate that this may be a behavioral phenotype that supports epidemiological data that women are more vulnerable than men in developing CUDs.

Relationship between cognitive performance and social rank in male and female cynomolgus macaques: Implications for the role of cognition in vulnerability to cocaine use disorder

Cocaine use disorder (CUD) currently has no FDA-approved pharmacological treatment. One of the most promising behavioral interventions is cognitive behavioral therapy. Still, there is a continuing need to understanding what makes an individual susceptible to CUD. A major goal of this study is to determine if cognitive performance can serve as a behavioral biomarker related to vulnerability to cocaine abuse. Previous studies have shown sex differences in vulnerability to cocaine based on social rank (Morgan et al., 2002; Nader et al., 2012). The goal of the present study is to evaluate cognitive performance as a potential biomarker for vulnerability to cocaine abuse, in socially housed cocaine-naïve female and male monkeys. In an earlier study involving newly formed social groups of female monkeys, performance on one cognitive domain, working memory using a delayed-match-to-sample task, showed social rank differences only during establishment of the social hierarchy; once the hierarchies were stable, there were no differences in working memory across social ranks (Kromrey et al., 2016). The present study differs from our earlier work by studying several cognitive domains in well-established, same-sex, male and female social groups (N=8/sex). Monkeys were trained to complete a battery of cognitive tasks which evaluated learning and memory (stimulus discrimination; SD and compound discrimination; CD), executive function (reversal learning; SDR) and behavioral flexibility (interdimensional shifting; ID, extradimensional shifting; and reversal, ED, EDR). The test battery consisted of monkeys performing all tasks (SD/SDR, CD, ID, ED/EDR) in 1-3 sessions; criteria for moving to the next task was 12/15 trials correct. All studies were performed in accordance with the FASEB Statement of Principles for the Use of Vertebrate Animals in Research and Education and Wake Forest's IACUC. We hypothesized that because earlier work had shown subordinate males and dominant females were more vulnerable to cocaine reinforcement, that they would show poorer cognitive performance relative to dominant males and subordinate females. In preliminary findings, dominant male and female monkeys made fewer total errors and required less trials to complete the battery compared with subordinate animals, in contrast to our hypothesis. Next, acquisition of cocaine reinforcement will be examined in an effort to replicate earlier findings and then the test battery will be repeated at various timepoints in order to evaluate the effects of cocaine on cognitive performance as a function of sex and social rank.

The bullies are the leaders of the next generation: Inherited aminergic neurotransmitter system changes in socially dominant zebrafish, Danio rerio

We studied the social hierarchy in zebrafish and assessed differences in neurotransmitters and behavior in the F1 generation offspring of dominant and subordinate zebrafish (Danio rerio). We used behavioral assays to study locomotion, ability to complete cognitive tasks, social interaction and aggression. To study the neurochemical changes, we applied quantitative polymerase chain reaction, high pressure liquid chromatography and immunohistochemistry. Social hierarchies were formed both by males and females when animals were kept in same sex pairs in the dyadic dominant-subordinate hierarchy test. The offspring of dominant animals were the leaders in social interactions, however aggression in the mirror-test was not altered in any group. Serotonin and noradrenaline levels were lower in the F1 generation subordinate animals when compared with dominant animals, but not compared with animals that were naïve to social hierarchy. The mRNA level of the rate-limiting enzyme in histamine synthesis, histidine decarboxylase, was significantly lower in dominant and subordinate larval zebrafish when compared with control animals. In the dominant adult zebrafish tyrosine hydroxylase 1 mRNA level was lower compared with control animals, whereas tyrosine hydroxylase 2 mRNA was not different. The result was verified with immunohistochemistry. There were gender specific differences between the dominant and subordinate animals, where the dominant females performed better in cognitive tasks such as the T-maze than subordinate females. This was not observed in males, as the behavior of the dominant and subordinate males did not differ. These results add to the understanding of the plastic nature of the central nervous system and show that neurochemical features in aminergic neurotransmitter systems are associated with social leadership and dominance.

The influence of male dominance in female Anastrepha curvicauda mate selection

Males of the papaya fruit fly, Anastrepha curvicauda Gerstaecker (former Toxotrypana curvicauda), defend a papaya fruit from rivals and males release their sex pheromone to attract and mate with females and offer them an oviposition site. While some aspects of the biology of A. curvicauda are known, such as its reproductive biology, its sex pheromone, and host selection, there is currently no information on the species mate selection process. This paper describes the precopulatory mating behavior of A. curvicauda and elucidates how intrasexual selection affects the mate selection process. We studied the precopulatory mating behavior of dominant and subordinate males and ethograms were devised. The effect of hierarchy was studied in non-choice and choice experiments. Male’s repertoire includes 15 behavioral elements, 12 precopulatory, one mating, and two postcopulatory (tandem and encounter). In non-choice experiments, dominant and subordinate males were accepted by females, but when females had the opportunity to choose among males, dominant males were significantly preferred over subordinate ones. The presence of a rival male modified the courting behavior of males and agonistic behavior among males was observed before and during mating.

Sexual Interference Behaviors in Male Adult and Subadult Tibetan Macaques (Macaca thibetana).

Simple SummarySexual interference behaviors (interruption/harassment) by male nonhuman primates can lead copulating individuals to separate and is hypothetically a form of male–male competition for access to sexually receptive females. Tibetan macaques (Macaca thibetana) provide an example of male sexual interference that can be used to discuss the sexual competition hypothesis. We found male sexual interference in this species showed significant seasonal variation. Age did not affect the proportion or type of interference behaviors that a male performed, but his social status did. Dominant males more often interrupted copulations. Subordinate males more often directed harassment behaviors toward dominant males, which reduced copulation duration, especially the post-ejaculatory phase of copulation. Our results suggest that sexual interference (interruption or harassment) may be a tactic to reduce the mating success of other males by either preventing ejaculation or reducing the duration of the post-ejaculatory phase, which is critical for sperm transport and, thus, reproductive success. Male nonhuman primate sexual interference, which includes copulation interruption and copulation harassment, has been related to reproductive success, but its significance has been challenging to test. Copulation interruption results in the termination of a copulation before ejaculation, whereas copulation harassment does not. We conducted this study using the all-occurrence behavior sampling method on sexual interference behaviors of seven adult and four subadult male Tibetan macaques (Macaca thibetana) in mating and non-mating seasons at Mt. Huangshan, China, from August 2016 to May 2017. Our results showed that males’ individual proportion of copulation interruption and harassment was higher during the mating season than during the non-mating season. In addition, dominant males more often performed interruption, whereas subordinate males more often performed harassment. We found no difference in the individual proportion of copulation interruption or harassment between adult and subadult males. Adult and subadult males both directed copulation interruption and harassment more often toward the mating male than toward the mating female. Lastly, the post-ejaculation phase of copulation was shorter when copulation harassment occurred than when it did not. Our results suggest that sexual interference may be an important mating tactic that adult and subadult males use in male–male sexual competition.

Women Managers’ Impact on Use of Family-friendly Measures among Their Subordinates in Japanese Firms

Using data from the Survey on Support for Work–Life Balance conducted in Japan, this study investigates the role of female managers in enhancing their male and female subordinates’ access to family-friendly measures in the workplace. Research on organisational gender inequality has proposed two contrasting perspectives regarding the impact of female managers on gender inequality, describing female managers as either ‘change agents’ or ‘cogs in the machine’. However, previous research has rarely investigated whether female managers address men’s limited access to family-friendly measures, which is often the hidden side of the coin of gender imbalance in male-dominated organisations. Results indicate that female managers were more likely to have subordinates who take parental leave and to exhibit stronger support for male subordinates’ family-related requests than male managers, although, like male managers, they reported feeling that managing their sections during these absences is a challenge. The implications of the findings are discussed.

Radical change: temporal patterns of oxidative stress during social ascent in a dominance hierarchy

Dominant individuals have priority access to mates and resources. However, high rank can be costly too, especially when it is maintained by intense agonistic behavior. Oxidative stress has been proposed as a potential cost of social dominance. However, social dominance hierarchies can be dynamic, and few studies have examined the cost of social dominance when males are changing status. We studied temporal changes in markers of oxidative stress during social ascent in the East African cichlid fish Astatotilapia burtoni. After removing the dominant male, males ascended from subordinate to dominant status. On the first day of social ascent, immediately after the dominant male removal, the newly dominant male showed lower levels of plasma total antioxidant capacity (TAC). However, we found that liver TAC and liver superoxide dismutase (SOD), an enzymatic antioxidant, were significantly upregulated on day 1 and 2 of social ascent, respectively. No temporal variation in nicotinamide adenine dinucleotide phosphate-oxidase (NADPH-oxidase) activity, blood DNA damage, and liver DNA damage was observed. By day 14, all markers of oxidative stress were similar to those observed in stable dominant males, which had higher levels of reactive oxygen metabolites (ROM) compared to subordinate males. We conclude that markers of oxidative stress vary dramatically during social ascent in a time- and tissue-dependent manner. Our study provides a more nuanced look at the oxidative cost of social dominance and highlights the importance of considering temporal changes in markers of oxidative stress during important life-history events. High social status gives priority access to resources but also entails costs. Since dominant individuals tend to have higher metabolic rates, oxidative stress could be a potential cost of high social status. Oxidative stress can occur when reactive oxygen species, produced during metabolic activities, cannot be effectively neutralized by antioxidants, leading to oxidative cellular damage. Social hierarchies can be dynamic, yet how the cost of rank varies when males are changing social status is unknown. We allowed subordinate males to ascend to dominant status in the cichlid fish Astatotilapia burtoni. At the beginning of social ascent when males suddenly increase aggressive behavior, the total antioxidant defense was lower in blood plasma, as expected, when males suddenly increase their metabolism during aggressive interactions. However, antioxidant defense was increased in the liver suggesting that males can compensate for the potential cost of becoming dominant. Circulating reactive oxygen metabolites gradually increased over time reaching levels similar to stable dominant males, possibly due to males upregulating their reproductive axis. Our results highlight that markers of oxidative stress can vary dramatically over time during important events in life.

Trade-offs between fighting and breeding: a social network analysis of bison male interactions.

In most polygynous species, males compete for access to females using agonistic interactions to establish dominance hierarchies. Typically, larger and stronger males become more dominant and thus gain higher mating and reproductive success over subordinate males. However, there is an inherent trade-off between time and energy invested in dominance interactions versus courtship and mating activities. Individuals may overcome this trade-off by selectively engaging in more effective mating tactics. North American bison (Bison bison) are a species of conservation concern that exhibit female-defense polygyny with two predominant mating tactics: (1) tending individual females; or (2) challenging tending males as a satellite and then mating opportunistically. Here, we use social network analysis to examine the relationship between position in the agonistic interaction network of bison males and their mating, reproductive success, and reproductive tactics and effort. To assess the potential for social network analysis to generate new insights, we compare male (node) centrality in the interaction network with traditional David’s score and Elo-rating dominance rankings. Local and global node centrality and dominance rankings were positively associated with prime-aged, heavy males with the most mating success and offspring sired. These males invested more effort in the “tending” tactic versus the “satellite” tactic, and they tended more females for longer periods during peak rut, when most females were receptive. By engaging in the most effective mating tactic, dominant males may mitigate the trade-off between allocating time and energy to agonistic interactions that establish dominance, versus courtship and mating. While less dominant males participated more in the alternative mating tactic, network analysis demonstrated that they were still important to the interaction network on both a local and global scale.