Alpha Males Research Articles

SEXUAL DIMORPHISM, DISPERSAL PATTERNS, AND BREEDING BIOLOGY OF THE TAIWAN YUHINA: A JOINT-NESTING PASSERINE

Abstract We studied the breeding ecology of Taiwan Yuhinas (Yuhina brunneiceps) at the Highlands Experiment Farm at Meifeng, National Taiwan University, in 1995 and from 1997–2002. The Taiwan Yuhina is a joint-nesting, cooperatively breeding species endemic to Taiwan. Males had significantly longer wing chords and tail lengths than females, probably due to sexual selection. Males also had a longer residence time at Meifeng than their female mates, which could be explained by philopatry being greater in males. Alpha males had a significantly longer residence time at Meifeng than beta males, but this was not the case for females, because females did not remain in the same group as males did after their mates disappeared. The breeding season was approximately 6 months long and multiple brooding was common. Nest building took 3 days, egg laying occurred over 3–4 days, the average incubation period was 14 days, and the nestling period was 12 days. Breeding success did not decrease later in the breeding season....

Mechanisms of sexual selection: Sexual swellings and estrogen concentrations as fertility indicators and cues for male consort decisions in wild baboons

Male mate-guarding episodes (‘consortships’), are taxonomically widespread, yet costly to individual males. Consequently, males should bias consortships toward females with whom the probability of conception is high. We combined data on consortships with visual scoring of sexual swellings and assays of fecal estrogen concentrations (fE) in a wild population of baboons ( Papio cynocephalus) to test the hypotheses that sexual swellings are reliable indicators of (1) within-cycle timing of ovulation, (2) differences in conception probability among females that differ in maturational stage, and (3) conceptive versus non-conceptive cycles of parous females. We also evaluated whether adult males might rely on swellings or other estrogen-dependent signals (e.g., fE) for mate-guarding decisions. We found that sexual swellings reflected conception probability within and among cycles. Adult males limited their consortships to the turgescent phase of cycles, and consorted more with adult females than with newly cycling adolescents. The highest ranking (alpha) males discriminated more than did males of other ranks; they (1) limited their consortships to the 5-day peri-ovulatory period, (2) consorted more with adult than with adolescent females, and (3) consorted more with adult females on conceptive cycles than on non-conceptive cycles, all to a greater extent than did males of other ranks. Male mate choice based on sexual swellings and other estrogenic cues of fertility may result in sexual selection on these female traits and enhance dominance-based reproductive skew in males. Alpha males are the least constrained in their mating behavior and can best take advantage of these cues to mate selectively.

Violent coalitionary attack by female mandrills against an injured alpha male

Female contact aggression against males is relatively rare in species in which the adult males are larger than the females, but it has the potential to influence group structure, male group membership, tenure, and dominance rank. We report an incident in which female mandrills living in a semi-free-ranging group in Franceville, Gabon, attacked a male that was apparently incapacitated after a fight with another male and was unable to escape. The attack involved the alpha male and did not occur in a sexual or infanticidal context. Other adult and adolescent males observed the attack, but when one adult male attempted to participate he was chased away by the females. This observation adds to reports of female coalitions excluding unwanted males from primate groups, or even killing them. The fact that this can also occur in mandrills suggests that females have a degree of control over male group membership, despite the large degree of sexual dimorphism in this species, and highlights the importance of coalitions in primate social organization.

Determinants of male reproductive success in wild long-tailed macaques (Macaca fascicularis)—male monopolisation, female mate choice or post-copulatory mechanisms?

One of the basic principles of sexual selection is that male reproductive success should be skewed towards strong males in species with anisogamous sex. Studies on primate multi-male groups, however, suggest that other factors than male fighting ability might also affect male reproductive success. The proximate mechanisms leading to paternity in multi-male primate groups still remain largely unknown since in most primate studies mating rather than reproductive success is measured. Furthermore, little research focuses on a female’s fertile phase. The aim of this study was to investigate the relative importance of male monopolisation and female direct mate choice for paternity determination. We also investigated the extent to which paternity was decided post-copulatory, i.e. within the female reproductive tract. We used a combined approach of behavioural observations with faecal hormone and genetic analysis for assessment of female cycle stage and paternity, respectively. The study was carried out on a group of wild long-tailed macaques living around the Ketambe Research Station, Gunung Leuser National Park, Indonesia. Our results suggest that both male monopolisation and post-copulatory mechanisms are the main determinants of male reproductive success, whereas female direct mate choice and alternative male reproductive strategies appear to be of little importance in this respect. Female cooperation may, however, have facilitated male monopolisation. Since paternity was restricted to alpha and beta males even when females mated with several males during the fertile phase, it seems that not only male monopolisation but also post-copulatory mechanisms may operate in favour of high-ranking males in long-tailed macaques, thus reinforcing the reproductive skew in this species.

Life history in male mandrills (Mandrillus sphinx): Physical development, dominance rank, and group association

We assess life history from birth to death in male mandrills (Mandrillus sphinx) living in a semifree-ranging colony in Gabon, using data collected for 82 males that attained at least the age of puberty, including 33 that reached adulthood and 25 that died, yielding data for their entire lifespan. We describe patterns of mortality and injuries, dominance rank, group association, growth and stature, and secondary sexual character expression across the male lifespan. We examine relationships among these variables and investigate potential influences on male life history, including differences in the social environment (maternal rank and group demography) and early development, with the aim of identifying characteristics of successful males. Sons of higher-ranking females were more likely to survive to adulthood than sons of low-ranking females. Adolescent males varied consistently in the rate at which they developed, and this variation was related to a male's own dominance rank. Males with fewer peers and sons of higher-ranking and heavier mothers also matured faster. However, maternal variables were not significantly related to dominance rank during adolescence, the age at which males attained adult dominance rank, or whether a male became alpha male. Among adult males, behavior and morphological development were related to a male's own dominance rank, and sons of high-ranking females were larger than sons of low-ranking females. Alpha males were always the most social, and the most brightly colored males, but were not necessarily the largest males present. Finally, alpha male tenure was related to group demography, with larger numbers of rival adult males and maturing adolescent males reducing the time a male spent as alpha male. Tenure did not appear to be related to characteristics of the alpha male himself.

Experimental test of female black howler monkey (Alouatta Pigra) responses to loud calls from potentially infanticidal males: Effects of numeric odds, vulnerable offspring, and companion behavior

During group defense, the contribution of female black howler monkeys (Alouatta pigra) may help deter male intruders; however, their involvement during natural intergroup encounters is facultative. Experimental playback trials simulating potentially infanticidal males were used to examine whether a female's reproductive investment and/or her group's relative fighting ability would influence her participation in loud call displays. Female howlers never responded to recordings without alpha male accompaniment, but their response patterns did not simply mimic his. For example, unlike alpha males, females with small, vulnerable offspring were no more likely than females without infants to participate in howling displays during playback trials. Further, although females without any small infants in their group got closer to speakers than females living in groups with small infants, males did not respond in the same way. To artificially simulate different "numeric odds" scenarios, recordings of one or three howling males (simulated intruders) were broadcast to females living in groups with 1-3 resident males. Responses were consistent with the hypothesis that females assessed intergroup fighting ability. As in alpha males, the weakest female responses occurred when the numeric odds were against their group. However, whereas alpha males participated most when numeric odds were in their favor, females had the most intense approach responses when the number of defending and intruding males was equal. Females appeared to use a cost-effective strategy, reserving their assistance for when their participation could have the greatest impact.

Mate Choice in Male Mandrills (Mandrillus sphinx)

AbstractMale primates that attempt to monopolize access to receptive females by mate‐guarding expend time and energy and risk injury, making reproduction costly. Males should therefore show mate choice and preferentially allocate mating effort to females that are likely to be fertile and those that will produce high‐quality offspring. Specifically, males should preferentially mate‐guard high‐ranking females rather than low‐ranking females, as such females are more likely to be fertile and are able to invest more in offspring. Males should also prefer parous females to nullipares, for similar reasons. Finally, males should avoid mating with close relatives, to avoid the deleterious effects of inbreeding. We investigated 13 group‐years of mate‐guarding observations for two semi‐free‐ranging groups of mandrills to examine the influence of these factors on male investment in mate‐guarding. We found that males mate‐guarded higher‐ranking females more than lower‐ranking females, and parous females more than nullipares. Female age, true relatedness and maternal kinship did not influence male mate‐guarding. Our results suggest that male mandrills do exercise mate choice for higher‐quality females, in the form of higher‐ranking and parous females. As alpha males are responsible for the great majority of mate‐guarding, this can lead to assortative mating, where high‐ranking males reproduce with high‐ranking females, and has important implications for social relationships and kin selection.

Male competition and paternity in wild chimpanzees of the Taï forest

In social animals, competition among males for mates affects individual reproductive success. The priority-of-access model attempts to account for the influence of demographic conditions within groups upon male reproductive success, but empirical data for testing this model are scarce. Our long-term study of chimpanzees in the Taï National Park, Côte d'Ivoire, encompasses a period of steady decrease in community size and fluctuating numbers of competing males and sexually receptive females. These demographic changes, in combination with genetic assessment of paternity for 48 offspring from three communities, allowed us to quantify the effects of varying levels of competition upon male reproductive success. On average, the highest-ranking male sired 50% of all analyzed offspring during a 14-year period from 1987-2000. Competition among males strongly decreased the relative reproductive success of the alpha male, such that the alpha male's rate of success decreased from 67% with few competitors to only 38% with four or more competitors. The increasing number of synchronously receptive females in large groups also reduced the proportion of paternities by the alpha male. Thus, patterns of paternity in Taï chimpanzees fit well the predictions of the priority-of-access model. We also found that despite the inability of dominants to monopolize reproduction, they achieved a higher reproductive rate in large multimale groups, because these have more females and a higher infant survival rate. Varied levels of male competition within communities seem to explain differences in the reproductive success of alpha males observed in different chimpanzee populations, and in other primate species.

Genetic diversity and reproductive success in mandrills (Mandrillus sphinx).

Recent studies of wild animal populations have shown that estimators of neutral genetic diversity, such as mean heterozygosity, are often correlated with various fitness traits, such as survival, disease susceptibility, or reproductive success. We used two estimators of genetic diversity to explore the relationship between heterozygosity and reproductive success in male and female mandrills (Mandrillus sphinx) living in a semifree ranging setting in Gabon. Because social rank is known to influence reproductive success in both sexes, we also examined the correlation between genetic diversity and social rank in females, and acquisition of alpha status in males, as well as length of alpha male tenure. We found that heterozygous individuals showed greater reproductive success, with both females and males producing more offspring. However, heterozygosity influenced reproductive success only in dominant males, not in subordinates. Neither the acquisition of alpha status in males, nor social rank in females, was significantly correlated with heterozygosity, although more heterozygous alpha males showed longer tenure than homozygous ones. We also tested whether the benefits of greater genetic diversity were due mainly to a genome-wide effect of inbreeding depression or to heterosis at one or a few loci. Multilocus effects best explained the correlation between heterozygosity and reproductive success and tenure, indicating the occurrence of inbreeding depression in this mandrill colony.

Male mating strategies and reproductive constraints in a group of wild tufted capuchin monkeys (Cebus apella nigritus)

Tufted capuchin monkeys (Cebus apella) provide an extreme example of active female sexual solicitation of males. In spite of being targeted by females for sex, males may delay copulation for hours or days. Data were collected on the sexual interactions in one wild capuchin group at the Estação Biológica de Caratinga in Brazil from September 1996 to August 1997. All successful conceptions during this year occurred in the dry season, yet sexual behavior was observed during 9 months of the year. This study tested whether male sexual response to female proceptivity was seasonally-mediated. Male consortship participation, solicitation of females, latency to copulation, and copulation frequency were compared between fertile and nonconceptive females. Seasonal patterns in copulation interference, mating style, and alternative mating strategies were also examined. Thirty-two copulations were observed. The alpha male was solicited for significantly more consortship days per female, but his mating success, in terms of copulation frequency, did not differ from that of two other adult males in the group. In the dry season, when the females were fertile, the males showed increased contest competition for mates, a higher frequency of alternative mating strategies against copulation interference, and increased monitoring of the females' condition. However, contrary to expectations, the alpha male's latency to copulation was significantly longer in the fertile season than in the nonconceptive months, and no males were observed to mate more than one time per day, even at the conceptive peak. Male mating strategies were affected by both season and rank, and there was evidence for reproductive constraints on males throughout the year. Limited male ejaculatory capacity and male choice in the timing of copulations within female proceptive phases may both be important factors in driving the sexual dynamics of this species.

Mate guarding and paternity in mandrills: factors influencing alpha male monopoly

We used long-term data on mate guarding and paternity in mandrills, Mandrillus sphinx, (1) to examine cycle day and cycle selection by males; (2) to examine associations between male rank, periovulatory mate guarding and paternity outcome; (3) to test the predictions of the priority-of-access model; and (4) to investigate factors influencing the ability of alpha males to monopolize females. Males mate-guarded on periovulatory days more than on other receptive days, and during conceptive cycles more than during nonconceptive cycles. Both periovulatory mate guarding and paternity outcome correlated significantly with male rank. Alpha males accounted for 94% of periovulatory mate guarding and 69% of paternity, confirming the existence of extremely high reproductive skew in this highly sexually dimorphic species. The fit of the observed distributions of mate guarding and paternity to predictions from the priority-of-access model was good, but in both cases the alpha males accounted for a greater proportion of reproduction than predicted. Mate guarding was a good predictor of paternity, but consistently overestimated the reproductive success of the alpha male. Splitting data into group-years revealed that the percentage of mate guarding by the alpha male decreased with increasing numbers of adult males, and the percentage of paternity decreased with increasing numbers of reproductive males (all postpubertal males). Furthermore, mate guarding became less effective as the number of reproductive males increased. We attribute this to the fact that only males aged 8 years or more mate-guarded, but that all males aged at least 3.8 years may sneak copulations, reducing the effectiveness of mate guarding and therefore reducing paternity concentration in the alpha male.

Reproductive partitioning among polyandrous alpha and beta pale chanting-goshawk males

This study investigates the reproductive and parental roles of polyandrous male pale chanting-goshawks, Melierax canorus, and speculatively reviews the fitness outcomes of different skew and relatedness scenarios. The study was conducted over five years in the Little Karoo, South Africa. Although, polyandrous males participated equally in building nests, provisioning prey and incubating, in the fertility window the dominant alpha males copulated 31–5 days before the females laid, whereas subordinate beta males only copulated 5–3 days before laying. If this copulation timing by alpha males was indicative of a high reproductive skew, alpha males breeding as full sibs could skew paternity in their favour (ratio 68:32) and produce 0.69 offspring equivalents. Under this scenario, they compensated beta males with indirect fitness benefits by allowing them to produce 0.54 offspring equivalents, equal to monogamous males. Alternatively, if beta males controlled reproduction while breeding with non-relatives under a high skew scenario, they would have to restrain themselves to avoid eviction and produce 0.28 offspring equivalents to allow the fitness of alpha males at least to equal that of monogamous males. I suggest that alpha males and their females altered their reproductive roles to accommodate beta males, thereby increasing their inclusive fitness, whereas beta males tolerated subordination to acquire reproductive skills that non-breeder males do not have access to.

Plumage and Internal Morphology of the "Prairie Grouse", <em>Tympanuchus cupido</em> × <em>phasianellus</em>, of Manitoulin Island, Ontario

I made comparisons among populations of Greater Prairie-Chickens, Sharp-tailed Grouse and their hybrids on Manitoulin Island of pinnae length, breast, flank and tail feather patterns, tail graduations, wing chord, and skeletal characteristics. Estimates of the proportion of hybrids from these individual characters ranged from 32% to 60%. Lek behaviour of hybrids was a mixture of the patterns of the parent species. The colour of the booming sacks varied and displayed the range between the parent species. There was a tendency with time for the characters of Prairie Chickens to decline coincident with an increase in Sharptailed Grouse characters. Both Prairie Chickens and Sharp-tailed Grouse are lek species in which an alpha male may consummate most of the the matings. The speed with which morphological change took place in Manitoulin Island is to be expected where a non-random mating system of this kind prevails.

GROUP-SIZE EFFECTS AND PARENTAL INVESTMENT STRATEGIES DURING INCUBATION IN JOINT-NESTING TAIWAN YUHINAS (YUHINA BRUNNEICEPS)

Abstract We investigated the effect of group size on incubation effort in Taiwan Yuhinas (Yuhina brunneiceps) at the Highlands Experimental Farm of National Taiwan University at Meifeng, Nantou County, central Taiwan, during 2000 and 2001. The Taiwan Yuhina is a joint-nesting, cooperatively breeding species endemic to Taiwan. We compared differences in parental investment among individuals of different sexes and status, explored the effect of group size on group incubation effort, and investigated whether individuals show compensatory reductions in care with respect to the number of females laying. Constancy of incubation increased as group size increased. Alpha females exhibited a significantly greater incubation effort than other individuals, but effort was similar among other group members. Both alpha males and females decreased their relative and absolute incubation effort as group size increased (i.e., there was a compensatory reduction in parental effort). However, beta pairs maintained a consistent...

'STONE AGE SOCIOLOGY'- OR SOCIOLOGY OF EARLY LANGUAGE-USING SOCIETY?

Runciman's puzzle in his subtle and provocative article, 'Stone Age sociology' (2005), is in effect 'how did our Stone Age ancestors come to solve the problem of order while living in groups lacking leaders or any formal jural or political institutions?' In this the Stone Age hunter-gatherer groups differ sharply from both the ape bands which preceded them and the more complex societies which followed domestication of plants and animals. 'Why was it that would-be [human] alpha males became unable to acquire and hold positions of power in a way their [ape] ancestors had done before them, and their descendants were to do again?' (2005: 131). For in the more complex societies which later appeared, differentiation of wealth and power lead to rank and hierar? chy, big men and chiefs, patronage, kings and armies. In his article on 'Violence and social? ity in human evolution' (1991), Bruce Knauft describes this shift for primates from ape dominance roles, to egalitarianism, and back to elaborated dominance roles as 'U-shaped'. And he points out that such a reversal is unusual to fmd in evolution. Here Runciman

Consequences of a One-male Harem Reproductive System and Inbreeding in a Captive Group of Cercopithecus solatus

In closed captive populations, where dispersal is not possible, kin recognition and behavioral avoidance are the only mechanisms by which closely related individuals can avoid inbreeding. In the absence of avoidance, a loss of genetic diversity is inevitable in successive generations. In the 1980s, the CIRMF in Gabon established a small breeding group of sun-tailed monkeys (Cercopithecus solatus) with 4 individuals, and subsequently 17 births have been registered. We aimed to describe via microsatellite genotyping the reproductive system in the colony of Cercopithecus solatus, to evaluate the loss of genetic diversity with succeeding generations, and to evaluate consequences of inbreeding depression on a measure of the lifespan reproductive success of females giving birth to inbred vs. noninbred offspring. During the 11-yr period for which data are available, only alpha males sired offspring, confirming a one-male social organization. They reproduced only during their period of tenure. Two of the 3 alpha males were responsible for all the infants born. Genetic diversity decreased and inbreeding coefficients increased with successive generations. Interbirth interval was increased following the birth of an inbred infant, indicating possible increased maternal costs of rearing inbred infants. Loss of genetic variability in this captive group of sun-tailed monkeys has led to significant inbreeding depression and demonstrates the importance of male-mediated gene flow in restricted one-male harem breeding groups.

The effect of new alpha males on female stress in free-ranging baboons

In chacma baboons, Papio hamadryas ursinus, young adult males often rise to the top of the dominance hierarchy shortly after immigrating to a new group. Such events are potentially disruptive for pregnant and lactating females because high-ranking immigrant males often commit infanticide. In this preliminary study, we assessed the effects of upheavals in the male hierarchy on the physiology of 18 females in a baboon group living in the Moremi Game Reserve, Botswana. We collected behavioural and hormonal data to examine the effects of two separate events, a natal male take-over and an immigrant male take-over, on female faecal glucocorticoids (fGC). While few females had elevated fGC concentrations in response to the natal male take-over, following the immigrant male take-over there was a significant rise in fGCs, but only among lactating and pregnant females. Analysis of behavioural data indicated that elevated fGC concentrations were unrelated to male aggression towards females, female–female aggression, or rates of female–female grooming. Furthermore, lactating females with a male ‘friend’ during the immigrant male take-over period had a less marked increase in fGCs and lower fGC concentrations overall than females without a male friend. Taken together, these results suggest that male social instability itself does not necessarily elicit a stress response from females. Rather, it is the specific male that rises to the alpha position that prompts a stress response, and only from the females at risk for infanticide. Finally, females with a male friend may perceive themselves to be at a reduced risk of infanticide.

Nepotistic mobbing behaviour in the Siberian jay, Perisoreus infaustus

Antipredator theory has rarely been invoked to explain why birds associate in kin groups. Instead, it has been argued that offspring delay dispersal in response to poor dispersal opportunities and changes in the social environment as a consequence of dispersal decisions have been overlooked. To test whether parents provide their offspring with nepotistic antipredator protection, we conducted a field experiment to investigate predator mobbing in the Siberian jay. We used models of a mounted hawk and owl, which represent the two main predators as confirmed by recoveries of killed radiotagged individuals. Kin groups mobbed the predator models for longer and uttered both more calls in total and more predator-specific calls than nonkin groups. However, not all categories of individual called equally. In particular, alpha males gave most calls, especially in the presence of their retained offspring. Unrelated immigrants behaved least cautiously and approached the models closer and for longer than any other individual category. Furthermore, jays mobbed the hawk model, their most dangerous predator, for longer and took fewer risks than they did when mobbing the owl model. Our experiments show that effort and risk taking while mobbing in the Siberian jay not only depend on the danger posed by the predator, but are also influenced by the social environment. Parents invest more in the presence of their offspring. We suggested that such nepotistic antipredator behaviour gives offspring an incentive to delay dispersal and that nepotism could therefore have a pivotal role for the evolution of kin group living in animals.

Amphibious communication with sound in hippos, Hippopotamus amphibius

The difference in acoustic impedance between air and water makes it difficult to communicate efficiently with sound in both media. Sounds made in either air or water, for example, are almost completely reflected at the boundary. Several species, however, may use amphibious communication. Here I report that hippos make sounds both in air and underwater, and, with their heads in an amphibious position (eyes and nostrils above water but mouth and throat submerged), are able to transmit sounds to both media simultaneously. Hippos on the surface respond to both natural production and playback of the surface component of a simultaneous amphibious sound (SAS) by calling in the amphibious position (territorial alpha males usually call first). Hippos underwater consistently surface immediately following an SAS, or the playback of the underwater component of an SAS, and usually call in a chorus that can spread in air from one territory to the next for long distances. I also found that hippos in the amphibious position respond to playback of underwater hippo screams that are inaudible in air, and also to natural underwater calls, suggesting that they can hear in air and water simultaneously. I discuss behaviour associated with amphibious communication and probable mechanisms for producing and receiving these sounds.

Wolves: Behavior, Ecology, and Conservation

L. D. Mech, L. Boitani (eds.). 2003. Wolves: Behavior, Ecology, and Conservation. The University of Chicago Press, Chicago, Illinois, and London, United Kingdom, 448 pp. ISBN ISBN 0-226-51696-2, price (hardbound), $49.00. One of the references most cited by wolf biologists has been Mech's (1970) seminal work, The Wolf: The Ecology and Behavior of an Endangered Species . It is one of the few work-related books that adorn my living room shelves. On 1 June, 1978, Dr. Mech autographed it for me as we sat at a 3-person table in a converted tool shed that served as the bunkhouse on the Kenai National Moose Range in Alaska. At the time, he was already the alpha male of North American wolf biologists, and I drove the refuge's garbage truck. As we talked, I felt inspired about the insights science was providing about this mythical creature, the wolf. Dave and Luigi Boitani are still the alpha wolves of the new and old worlds, respectively, and I still basically clean up after people, but we are fortunate to have lived during a time when public interest in and research about wolves flourished. Wolves don't always make people's lives better, but wolves always make people's lives more interesting. Dave's and Luigi's work has fledged a host of outstanding biologists since the 1970s, and, to our great fortune, they were able to twist enough arms and call in enough old favors to …