Alpha Males Research Articles

Non-linear ascension in a reproductive hierarchy of the Blue Manakin (Chiroxiphia caudata)

Blue Manakin Chiroxiphia caudata (Pipridae) has a lek mating system in which males cooperate in teams of two or more individuals for courtship displays to females. Males ascend through a dominance hierarchy to assume the rank of alpha male. Only alpha males copulate with females. In this study, we describe the ascension of a male to the alpha rank following the disappearance of the previous alpha male. The study was conducted in the seasonal Atlantic Forest of Southern Brazil. We observed nine banded males at two adjacent leks. The gamma male at the more successful lek also acted as an alpha male at a less successful lek 314 m away. Upon the disappearance of the alpha male at the more successful lek, the gamma gave up his alpha rank at the less successful lek and ascended to the alpha rank at the more successful lek, bypassing the beta male. Although a previous study suggests a strictly linear dominance hierarchy in C. caudata, with beta male ascending to alpha status, our results suggest that the rising to become the alpha male may be a more flexible and dynamic process than previously reported.

Movement initiation in groups of feral horses

Herds of ungulates, flocks of birds, swarms of insects and schools of fish move in coordinated groups. Computer models show that only one or very few animals are needed to initiate and direct movement. To investigate initiation mechanisms further, we studied two ways in which movement can be initiated in feral horses: herding, and departure from the group. We examined traits affecting the likelihood of a horse initiating movement i.e. social rank, affiliative relationships, spatial position, and social network. We also investigated whether group members join a movement in dominance rank order. Our results show that whereas herding is exclusive to alpha males, any group member may initiate movement by departure. Social bonds, the number of animals interacted with, and the spatial position were not significantly associated with movement initiation. We did not find movement initiation by departure to be exclusive to any type of individual. Instead we find evidence for a limited form of distributed leadership, with higher ranking animals being followed more often.

Hormonal correlates of male life history stages in wild white-faced capuchin monkeys (Cebus capucinus)

Much attention has been paid to hormonal variation in relation to male dominance status and reproductive seasonality, but we know relatively little about how hormones vary across life history stages. Here we examine fecal testosterone (fT), dihydrotestosterone (fDHT), and glucocorticoid (fGC) profiles across male life history stages in wild white-faced capuchins (Cebus capucinus). Study subjects included 37 males residing in three habituated social groups in the Área de Conservacíon Guanacaste, Costa Rica. Male life history stages included infant (0 to <12months; N=3), early juvenile (1 to <3years; N=10), late juvenile (3 to <6years; N=9), subadult (6 to <10years; N=8), subordinate adult (⩾10years; N=3), and alpha adult (⩾10years; N=4, including one recently deposed alpha). Life history stage was a significant predictor of fT; levels were low throughout the infant and juvenile phases, doubled in subadult and subordinate adults, and were highest for alpha males. Life history stage was not a significant predictor of fDHT, fDHT:fT, or fGC levels. Puberty in white-faced capuchins appears to begin in earnest during the subadult male phase, indicated by the first significant rise in fT. Given their high fT levels and exaggerated secondary sexual characteristics, we argue that alpha adult males represent a distinctive life history stage not experienced by all male capuchins. This study is the first to physiologically validate observable male life history stages using patterns of hormone excretion in wild Neotropical primates, with evidence for a strong association between fT levels and life history stage.

Interactions between social structure, demography, and transmission determine disease persistence in primates.

Catastrophic declines in African great ape populations due to disease outbreaks have been reported in recent years, yet we rarely hear of similar disease impacts for the more solitary Asian great apes, or for smaller primates. We used an age-structured model of different primate social systems to illustrate that interactions between social structure and demography create ‘dynamic constraints’ on the pathogens that can establish and persist in primate host species with different social systems. We showed that this varies by disease transmission mode. Sexually transmitted infections (STIs) require high rates of transmissibility to persist within a primate population. In particular, for a unimale social system, STIs require extremely high rates of transmissibility for persistence, and remain at extremely low prevalence in small primates, but this is less constrained in longer-lived, larger-bodied primates. In contrast, aerosol transmitted infections (ATIs) spread and persist at high prevalence in medium and large primates with moderate transmissibility;, establishment and persistence in small-bodied primates require higher relative rates of transmissibility. Intragroup contact structure – the social network - creates different constraints for different transmission modes, and our model underscores the importance of intragroup contacts on infection prior to intergroup movement in a structured population. When alpha males dominate sexual encounters, the resulting disease transmission dynamics differ from when social interactions are dominated by mother-infant grooming events, for example. This has important repercussions for pathogen spread across populations. Our framework reveals essential social and demographic characteristics of primates that predispose them to different disease risks that will be important for disease management and conservation planning for protected primate populations.

Tourism and Infant-Directed Aggression in Tibetan Macaques (Macaca thibetana) at Mt. Huangshan, China

ABSTRACTPrevious studies of habituated Tibetan macaques (Macaca thibetana) at Mt. Huangshan, China demonstrated the negative impact that some tourism management strategies had on monkeys' annual infant mortality, but data on precise causes and perpetrators of infant injuries were not available. We worked at the same site and recorded rates of aggression that older monkeys directed toward group infants as a function of tourist numbers and proximity. We found a negative correlation between the number of people on the viewing platform and the frequency of monkeys' aggression toward the group's infants, but the effect is slight. We noted that infant-directed aggression (IDA) was more likely to occur in the provisioning zone where tourists bounded the monkeys on two sides, despite the fact that infants spent very little time in that location. The alpha and beta males engaged in more IDA than expected, while the other three adult males, adult females, and juveniles exhibited less IDA than expected. Males' IDA included biting, chasing, grabbing, and pushing. Adult females bit and grabbed mostly their own infants in the contexts of punishment and weaning. Juveniles' IDA was uncommon and consisted mostly of open-mouth threats. To minimize the severity and frequency of male-toinfant IDA, we recommend that sections of the tourist viewing platform be closed off so that tourists do not surround the monkeys, particularly when infants are near the viewing platforms and tourist numbers are few. The rule against tourists feeding monkeys should also be strictly enforced, so that altercations between the highest-ranked males and other group members, particularly infants, are less likely to occur.

Hooligans: nice guys or the last alpha males? A study of football supporters’ self-image

There are several problems with using the terms hooligan and hooliganism, as these are not emotionally neutral. The media as well as other parties use these terms uncritically to indicate a number of different phenomena. I will argue about the importance of understanding the complexity of the various aspects of supportership. This includes an understanding of the many facets of supportership as well as the numerous different contexts in which the people involved are acting in. The article clarify how Swedish football supporters – labelled hooligans by the media, sports clubs and the general public – describe themselves, their background, how they regard hooliganism, violence and why they engage in it. The study is based on interviews, and the informants’ self-image and opinions about hooligans and hooliganism will be analysed using the concept of identity as well as masculinity theory.

Perseverance and food sharing among closely affiliated female chimpanzees

Chimpanzees (Pan troglodytes) have been frequently observed to share food with one another, with numerous hypotheses proposed to explain why. These often focus on reciprocity exchanges for social benefits (e.g., food for grooming, food for sex, affiliation, kinship, and dominance rank) as well as sharing based on begging and deterring harassment. Although previous studies have shown that each of these hypotheses has a viable basis, they have only examined situations in which males have preferential access to food whereby females are required to obtain the food from males. For example, studies on male chimpanzee food sharing take advantage of successful crop-raids and/or acquisitions of meat from hunting, situations that only leave females access to food controlled by male food possessors. This begs the question how and with whom might a female chimpanzee in sole possession of a high-quality food item choose to share? In two large captive groups of chimpanzees, we examined each of the hypotheses with female food possessors of a high-quality food item and compared these data to a previous study examining food transfers from male chimpanzees. Our results show that alpha females shared significantly more with closely affiliated females displaying perseverance, while kinship and dominance rank had no effect. This positive interaction between long-term affiliation and perseverance shows that individuals with whom the female possessor was significantly affiliated received more food while persevering more than those with neutral or avoidant relationships towards her. Furthermore, females with avoidant relationships persevered far less than others, suggesting that this strategy is not equally available to all individuals. In comparison to the mixed-sex trials, females chose to co-feed with other females more than was observed when the alpha male was sharing food. This research indicates that male and female chimpanzees (as possessors of a desired food item) share food in ways influenced by different factors and strategies.

Death of the Alpha: Within‐Community Lethal Violence Among Chimpanzees of the Mahale Mountains National Park

Chimpanzees (Pan troglodytes) are capable of extreme violence. They engage in inter-group, sometimes lethal, aggression that provides the winners with an opportunity to enlarge their territory, increase their food supply and, potentially, attract more mates. Lethal violence between adult males also occurs within groups but this is rare; to date, only four cases (three observed and one inferred) have been recorded despite decades of observation. In consequence, the reasons for within-group lethal violence in chimpanzees remain unclear. Such aggression may be rare due to the importance of coalitions between males during inter-group encounters; cooperation between males is also thought to be key in the defense or advancement of social rank within the group. Previous accounts of within-group lethal violence concern victims who were low-ranking males; here we provide the first account of the killing of an incumbent alpha male by a coalition of adult males from the same community. We found no clear evidence that the alpha male's position was under threat during the months before the lethal attack: the male dominance hierarchy was highly stable, with low rates of male-male aggression, and there were no significant changes in social interactions (i.e. grooming and aggression) between the alpha male and the other adult males. Two of the four attackers were former alpha males and were the individuals with whom the victim appeared, in the period preceding his death, to be most strongly affiliated: his most frequent grooming partners and those with whom he spent most time in proximity. The lethal attack triggered a period of instability in the male hierarchy and was likely an opportunistic attempt to seize alpha status by the third-ranking male.

Mating Systems and Multiple Paternity in the Estuarine Crocodile (Crocodylus porosus)

Microsatellite markers were used to investigate the mating system of the Estuarine Crocodile (Crocodylus porosus). Three-hundred and eighty-six hatchlings from 13 clutches from a wild Northern Territory population, and 364 hatchlings from 21 clutches from a captive North Queensland population, were sampled. All samples were genotyped across five microsatellite loci. Multiple paternity was found in 69% of clutches in the wild population compared to 38% of clutches in the captive population. Up to three possible fathers were indicated in some clutches. Shared paternity was suggested by the presence of a common paternal genotype within two clutches in the wild population and among up to three clutches from a large shared pen in the captive population. The probability of detecting multiple paternity at all loci was high; 95% in the wild population and 98% in the captive population. There was no evidence of increased hatching success in the clutches that indicated multiple paternity compared to single paternity clutches in either population (P = 0.43 to P = 0.67). It is unknown whether the occurrence of multiple paternity in C. porosus is a result of multiple mating within the same breeding season or of sperm stored from matings in a previous season. These results suggest the genetic mating system for C. porosus is not polygynous but more likely promiscuous, and there is no evidence of dominant alpha males who control paternity in large areas.

Does cooperation increase helpers' later success as breeders? A test of the skills hypothesis in the cooperatively displaying lance‐tailed manakin

Experience improves individual performance in many tasks. Pre-breeding cooperation may provide important experience that improves later success as a breeder, offering one compelling explanation for why some individuals delay reproduction to help others breed (the 'skills hypothesis'). However, confounding effects of age, quality and alternative selective benefits have complicated rigorous tests of this hypothesis. Male lance-tailed manakins perform cooperative courtship displays involving partnerships between unrelated alpha and beta males, and alphas monopolize resulting copulations. Beta males therefore do not receive immediate direct or indirect fitness benefits, but may gain skills during cooperation that increase their later success as an alpha. To date, however, the effect of cooperative experience on later success as a breeder has never been tested in any cooperatively displaying taxon. The effects of prior cooperative experience on reproductive success of alpha lance-tailed manakins were analysed in a mixed model framework using 12 years of information on cooperative experience and annual and lifetime genetic reproductive success for 57 alpha males. Models included previously identified effects of age and alpha tenure. Individual-level random effects controlled for quality differences to test for an independent influence of beta experience on success. Males accumulated up to 5 years of beta experience before becoming alphas, but 42·1% of alphas had no prior beta experience. Betas became alphas later in life, and experienced significantly lower reproductive success in their final year as alpha than males that were never beta, but did not have higher lifetime success or longer alpha tenures. Differences in patterns of annual siring success were best explained by age-dependent patterns of reproductive improvement and senescence among alphas, not beta experience. Cooperative experience does not increase relative breeding success for male lance-tailed manakins. Importantly, beta cooperation seems to be an alternative reproductive tactic that yields fitness payoffs equivalent to a non-cooperative route to alpha status, if population growth rate is stable.

A New Color Morph of the Southern Purple-faced Langur (Semnopithecus vetulus vetulus) from the Rainforests of Southwestern Sri Lanka

The southern purple-faced langur (Semnopithecus vetulus vetulus) is endemic to Sri Lanka and is listed as Endangered on the IUCN Red List. Following several decades of widespread deforestation in the country, viable habitat has been severely reduced for these arboreal, folivorous primates. Living close to densely populated human settlements has lead to further conservation difficulties. They have adapted to exploiting cultivated fruits in home gardens resulting in human-primate conflict, besides confronting electrocution hazards when crossing roads using power lines. The opening of the Colombo-Matara Expressway has also posed a threat, with the possibility of troops from either side becoming genetically isolated. Twenty-six troops were studied from 2007 to 2011 in the southwestern districts of Galle and Matara; of these, 14 contained one or more individuals with an atypical pelage coloration, which we call here a white color morph Two white alpha males were documented, along with adults, juveniles, and young of both sexes, totaling 30 individuals. The troops around Deniyaya and Getabarawa villages contained members that showed a distinct pelage, and all of the members of these troops had dissimilar cranial features and body size compared to other S. v. vetulus. Molecular analysis is now required to discover the genetic basis for this variation and any possible competitive advantages associated with its spread, with the possibility that this may originate a new subspecies. The discovery of a new color morph may provide an additional opportunity to promote primate conservation; greater national support is urgently needed considering the perilous future facing S. vetulus. Further research prospects and conservation recommendations are discussed in this paper.

Established populations of Paracerceis sculpta (Isopoda) in the Northern Gulf of Mexico

A population of the isopod Paracerceis sculpta Holmes, 1904 was found in Port Aransas, Texas in Northern Gulf of Mexico in 2009, the first report of the species in the Gulf of Mexico. The last large isopod survey in the area was conducted in 1981 implying that P. sculpta invaded some time in the last 28 years. Here, we show size frequency distributions of 858 individuals, alpha males (mean length = 5.48 mm ± 0.09 SE), pre-alpha males (3.94 mm ± 0.15), females (2.76 mm ± 0.03) and juveniles (1.24 mm ± 0.02). Beta and gamma males are absent in Texas, a major contrasting difference between the invasive and native populations.

Urine-washing in white-faced capuchins: a new look at an old puzzle

Some primates regularly wash their hands and feet with urine. This behaviour is outwardly similar to scent marking in other mammals, but it differs in that the urine is applied to the bare skin of the hands and feet rather than rubbed into the fur or applied directly onto an object in the environment. Empirical evidence for the functional significance of urine-washing remains inconsistent. We used rigorous statistical methods to examine environmental and social influences on urine-washing behaviour, using 4380 observation hours on five groups of wild white-faced capuchins (Cebus capucinus) in Costa Rica. Urine-washing frequencies were most strongly affected by environmental dryness, both within and between seasons, with markedly less urine-washing during humid conditions. Increased individual activity levels also promoted urine-washing. Among females, urine-washing was less frequent during lactation than during pregnancy and other reproductive states. Among males, urine-washing frequencies were greater in alpha males, who also exhibited a ‘vigorous’ form of urine-washing that may be functionally distinct. During the dry season, 3/5 groups exhibited more urine-washing than expected near fruit trees, but across groups there were no consistent spatial patterns for urine-washing with respect to water resources, home range overlap zones, core areas, inter-group encounter zones, and the home-range periphery. Urinewashing appears to differ fundamentally from common forms of mammalian scent marking. We suggest that its function is primarily mechanical, perhaps to apply a sticky residue to the hands and feet to improve grip on dry, arboreal substrates. Lesser signalling functions may include sexual signalling and resource labelling.

The association of intergroup encounters, dominance status, and fecal androgen and glucocorticoid profiles in wild male white-faced capuchins (Cebus capucinus).

Androgens play a role in male reproductive competition, frequently via aggression, while glucocorticoids are associated with the stress response. However, the relationships of these hormones with different sources of competition (intra- vs. intergroup) and dominance status are highly variable. Here, we consider the fecal androgen (fA) and glucocorticoid (fGC) profiles of alpha and subordinate male Cebus capucinus in the context of intergroup competition during a rare period of low intragroup competition (i.e. all females were either pregnant or lactating). Intergroup encounters (IGEs) are a long-term reproductive strategy in male white-faced capuchins, enabling them to assess the composition of neighboring groups. IGEs pose a threat to resident males as these can result in injury or death, loss of dominance rank, group eviction, and group takeovers that are frequently associated with infanticide. From February to July 2007, fecal samples were collected from eight males in three groups of white-faced capuchins in the Santa Rosa Sector of the Área de Conservación Guanacaste, Costa Rica. IGE rate was positively associated with both fA and fGC levels, indicating that IGEs are perceived as reproductive challenges by resident males, and may be associated with elevated metabolic costs. Alpha males sire the majority of group offspring and, accordingly, the threat of IGEs to both future (via rank loss or eviction) and current (via infanticide) reproductive success is greater than for subordinate males. Consistent with this observation, alpha males had higher fA and fGC levels than subordinate males. Given that all females were either pregnant or lactating and pronounced overt intragroup competition was absent, we interpret the difference in hormone profiles of alpha and subordinate males as being primarily associated with variation in the perceived threats of IGEs according to dominance status. Future studies should focus on the interaction of intra- and intergroup competition by examining hormone levels in the presence of periovulatory females.

Strong gender differences in reproductive success variance, and the times to the most recent common ancestors

The Time to the Most Recent Common Ancestor (TMRCA) based on human mitochondrial DNA (mtDNA) is estimated to be twice that based on the non-recombining part of the Y chromosome (NRY). These TMRCAs have special demographic implications because mtDNA is transmitted only from mother to child, while NRY is passed along from father to son. Therefore, the former locus reflects female history, and the latter, male history. To investigate what caused the two-to-one female–male TMRCA ratio rF/M=TF/TM in humans, we develop a forward-looking agent-based model (ABM) with overlapping generations. Our ABM simulates agents with individual life cycles, including life events such as reaching maturity or menopause. We implemented two main mating systems: polygynandry and polygyny with different degrees in between. In each mating system, the male population can be either homogeneous or heterogeneous. In the latter case, some males are ‘alphas’ and others are ‘betas’, which reflects the extent to which they are favored by female mates. A heterogeneous male population implies a competition among males with the purpose of signaling as alpha males. The introduction of a heterogeneous male population is found to reduce by a factor 2 the probability of finding equal female and male TMRCAs and shifts the distribution of rF/M to higher values. In order to account for the empirical observation of the factor 2, a high level of heterogeneity in the male population is needed: less than half the males can be alphas and betas can have at most half the fitness of alphas for the TMRCA ratio to depart significantly from 1. In addition, we find that, in the modes that maximize the probability of having 1.5<rF/M<2.5, the present generation has 1.4 times as many female as male ancestors. We also tested the effect of sex-biased migration and sex-specific death rates and found that these are unlikely to explain alone the sex-biased TMRCA ratio observed in humans. Our results support the view that we are descended from males who were successful in a highly competitive context, while females were facing a much smaller female–female competition.

Rise to Power: A Case Study of Male Fecal Androgen and Cortisol Levels before and after a Non-Aggressive Rank Change in a Group of Wild White-Faced Capuchins (Cebus capucinus)

We examined fecal androgen and cortisol levels in three adult male white-faced capuchin monkeys (Cebus capucinus) before and after a non-aggressive rank increase in one habituated group residing in the Santa Rosa Sector of the Área de Conservación Guanacaste, Costa Rica. Fecal samples (n = 116) were collected opportunistically between July 2006 and July 2007. Alpha males had higher mean androgen levels than subordinates, and acquisition of the alpha position was linked to an immediate increase in mean androgens. Cortisol levels also increased in the alpha male after acquisition of his new rank, though this increase was delayed relative to the change in rank. These results indicate that, during a non-aggressive rank change, androgen and cortisol levels in male white-faced capuchins are physiological responses to dominance rank, rather than precursors that facilitate rank acquisition.

Impartial third-party interventions in captive chimpanzees: a reflection of community concern.

Because conflicts among social group members are inevitable, their management is crucial for group stability. The rarest and most interesting form of conflict management is policing, i.e., impartial interventions by bystanders, which is of considerable interest due to its potentially moral nature. Here, we provide descriptive and quantitative data on policing in captive chimpanzees. First, we report on a high rate of policing in one captive group characterized by recently introduced females and a rank reversal between two males. We explored the influence of various factors on the occurrence of policing. The results show that only the alpha and beta males acted as arbitrators using manifold tactics to control conflicts, and that their interventions strongly depended on conflict complexity. Secondly, we compared the policing patterns in three other captive chimpanzee groups. We found that although rare, policing was more prevalent at times of increased social instability, both high-ranking males and females performed policing, and conflicts of all sex-dyad combinations were policed. These results suggest that the primary function of policing is to increase group stability. It may thus reflect prosocial behaviour based upon “community concern.” However, policing remains a rare behaviour and more data are needed to test the generality of this hypothesis.

Sneaky Monkeys: An Audience Effect of Male Rhesus Macaques (Macaca mulatta) on Sexual Behavior

Males and females have different sexual interests and subsequently may show conflicting sexual strategies. While dominant males try to monopolize females, promiscuity benefits females and subordinate males. One way to escape monopolization by dominant males is to copulate in their absence. We tested this inhibitory effect of males on the sexual behavior of their group members in captive group-living Rhesus macaques. Copulations between females and nonalpha males almost exclusively took place when the alpha male was out of sight. Furthermore, the inhibiting effect was not unique for the alpha male. An upcoming nonalpha male also inhibited copulations of its group members, and three other nonalpha males inhibited female copulation solicitations. Females adjusted their behavior to the presence of bystander males, as they initiated and accepted initiations more often in absence than in presence of bystander males. Although not significant, in males, a similar pattern was found. The observed reduction in mating behavior in presence of bystander males is in accordance with an "audience effect," in which the behavior is modulated in relation to the presence or absence of third parties. This audience effect may serve as an important mechanism to reduce (aggressive) interruptions of subordinate male copulations.

Impact of Body Reserves on Energy Expenditure, Water Flux, and Mating Success in Breeding Male Northern Elephant Seals

In capital breeders, individual differences in body size and condition can impact mating effort and success. In addition to the collateral advantages of large body size in competition, large nutrient reserves may offer advantages in endurance rivalry and enable the high rates of energy expenditure associated with mating success. We examined the impacts of body reserves and dominance rank on energy expenditure, water flux, mating success, and breeding tenure in the adult male northern elephant seal, a polygynous, capital breeder. Adult males expended energy at a rate of 159 ± 49 MJ d (-1), which is equivalent to 3.1 times the standard metabolic rate predicted by Kleiber's equation. Despite high rates of energy expenditure and a long fasting duration, males spared lean tissue effectively, deriving a mean of 7% of their metabolism from protein catabolism. Body composition had a strong impact on the ability to spare lean tissue during breeding. When controlling for body size, energy expenditure, depletion of blubber reserves, and water efflux were significantly greater in alpha males than in subordinate males. Large body size was associated with increased reproductive effort, tenure on shore, dominance rank, and reproductive success. Terrestrial locomotion and topography appeared to strongly influence energy expenditure. Comparisons with conspecific females suggest greater total seasonal reproductive effort in male northern elephant seals when controlling for the effects of body mass. In polygynous capital breeding systems, male effort may be strongly influenced by physiological state and exceed that of females.

Evolution of ape and human mating systems

Humans ( Homo sapiens) generally form multiple-male–multiple-female groups that include multiple family units. This social structure is maintained because dominant males do not monopolize females and, thus, allow subordinate males to mate, and human females are not generally promiscuous. Although apes show great variation in mating systems, the human-type mating system is unique among primates. The mating systems of apes and humans have evolved in response to their adaptation to different ecological conditions. We created and analyzed a mathematical model to investigate the conditions for each type of mating system to evolve. We focused on the mating strategy of alpha males and the mating and grouping strategies of females. We defined the human-type mating system as one with multiple-male–multiple-female groups in which alpha males do not monopolize females and females are not promiscuous. We demonstrated that the human-type mating system could evolve when a large group is advantageous and the cost of female promiscuity is great. Moreover, the human- and Pan-type mating systems can be bistable. Our results shed light on the origin of the human family.