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Female (black) and male (gray) body mass measurements in kilograms across age categories in Verreaux’s sifaka (Propithecus verreauxi) at Kirindy Mitea National Park. Points indicate individual mass measurements; bars indicate mean body mass in each age category.
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Conflicts between individuals are common among animals, with power dynamics often biased toward a particular sex. However, individuals across species exert power differently depending on the primary source of that power. Dominance-based power depends on fighting ability (e.g., greater body size) whereas leverage-based power depends on resources tha...
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... If inter-sexual outcomes were in terms of dominance, size would be a major factor in who wins contests, but maturity, not size, is determinant (Voyt, Sandel, Ortiz & Lewis, 2019). ...
Dominance hierarchy (DH) is never bi-(inter-)sexual. Rare ostensible female dominance (over males) is not even amenable to modelling, and actually is male non-engagement in dominance terms (deference, not submission). Any female hierarchy is not DH, as it is not contest-based, but from either mutually signalled differential fecundity or maternal rank inheritance. Otherwise, apparent female hierarchy is either non-dominance-based first-among-equals-winner-takes-all-sociality of a female sole reproducer, or a loose artefact of ad hoc resource competition. DH entails neuro-hormonally processing winner/loser effects, for which there is evidence only in males, and requires the Y chromosome's SRY gene. Male-specificity is anticipated from the male root function of genetic filtration / mutational cleansing, necessitating male ranking in terms of genomic integrity.
... In some animal societies, females are more powerful than males. This phenomenon is often called "female dominance, " but both theoretical (Hand, 1986;Smuts, 1987;Lewis, 2002Lewis, , 2018Lewis, , 2020 and empirical (Lewis, 2004;Surbeck and Hohmann, 2013;Young et al., 2017;Voyt et al., 2019) work suggests that female power over males can also be leverage, i.e., where female power over males arises from an asymmetry in intrinsic economic resources rather than an asymmetry in fighting abilities (Hand, 1986;Lewis, 2002Lewis, , 2018Lewis, , 2020. For example, the reproductive cycles, internal gestation, and lactation of female mammals can result in operational sex ratios that are highly male skewed (Emlen and Oring, 1977), i.e., where the number of sexually active males in a population greatly exceeds the number of sexually available females. ...
... Under this situation, having a fertilizable egg can be an important source of economic power (i.e., leverage) for females (Noë et al., 1991;Lewis, 2002Lewis, , 2004Lewis, , 2018Lewis, , 2020. Indeed, fertilization potential (a source of leverage) predicts intersexual status in sifaka, but sexual size dimorphism within a dyad (a source of dominance) does not (Voyt et al., 2019). Similarly, mating opportunities are a source of female leverage in bonobos that results in reduced intersexual aggression by males (Surbeck and Hohmann, 2013). ...
... For example, bonobo males do not exhibit aggression toward females when mating has a high probability of resulting in a conception (Surbeck and Hohmann, 2013), suggesting that the value of a female as a mating partner is discounted at other times. Consistent with the hypothesis that the value of a female's fertilizable egg varies with her experience and success at mothering, male sifaka are more submissive toward successful mothers than nulliparous females or parous females who have not yet successfully reared an infant, indicating that successful mothers have more leverage than other females in their relationships with males (Voyt et al., 2019). In other words, intersexual power can be highly dynamic, contextual, and dependent on the individuals in the dyad (Lewis, 2002). ...
Female mammals employ reproductive strategies (e.g., internal gestation) that result in power asymmetries specific to intersexual dyads. Because the number of eggs available for fertilization at any given time for most mammals is quite limited, having a fertilizable egg is potentially an important source of economic power for females. Control over mating opportunities is a source of intersexual leverage for female Verreaux’s sifaka ( Propithecus verreauxi ). We examined economic factors thought to influence the value of mating opportunities, and, thus, the extent of female leverage: kinship and market effects. Using a longitudinal dataset of agonistic interactions collected during focal animal sampling of all adult individuals in 10 social groups from 2008 to 2019, we tested the effects of relatedness, female parity, reproductive season, and adult sex ratio (population and group) on (1) the direction of submissive signaling and (2) which sex won a contested resource. While 96% of the acts of submission were directed from males toward females, females only won a third of their conflicts with males. Thus, our study has implications for evolutionary explanations of female-biased power. If female power evolved due to their greater need for food and other resources, then intersexual conflicts would be expected to result in males more consistently relinquishing control of resources. As expected, males were more likely to chatter submissively toward successful mothers, during the mating season, and when the sex ratio was male-biased. Although females generally had less power to win a conflict when their fertilizable egg was less valuable (when they were nulliparous or unsuccessful mothers or when interacting with male kin) and with an increasing female-bias in the sex ratio, this ability to win additionally was influenced by which sex initiated the conflict. Our study demonstrates that female leverage can be influenced by the supply and demand for mating opportunities, but evoking submission does not translate into winning a resource. Indeed, intersexual power is dynamic, contextual, and dependent on the individuals in the dyad.
... Females won 91% of intersexual conflicts and could dominate 83% of males (Kappeler et al., 2009). In another study, four groups of Verreaux's sifakas were observed for 4,965 h over a period of 9 years in Kirindy Mitea National Park (Voyt et al., 2019). A total of 483 decided agonistic interactions were observed. ...
... Second, an ontogenetic perspective suggests that the ability of females to win agonistic interactions with males emerges in close temporal proximity with sexual maturity because young females in ringtailed lemurs (Pereira, 1993), Verreaux's sifakas (Voyt et al., 2019) and gray mouse lemurs (Hohenbrink et al., 2015a,b) begin eliciting male submission at that developmental stage. Because these species represent different families, this functional relationship between female dominance and female reproduction is presumably ancestral for lemurs, but additional studies on the ontogeny of female dominance would be welcome. ...
The extant primates of Madagascar (Lemuriformes) represent the endpoints of an adaptive radiation following a single colonization event more than 50 million years ago. They have since evolved a diversity of life history traits, ecological adaptations and social systems that rivals that of all other living primates combined. Their social systems are characterized by a unique combination of traits, including the ability of adult females to dominate adult males. In fact, there is no other group of mammals in which female dominance is so widespread. Yet, recent research has indicated that there is more interspecific variation in lemur intersexual relationships than previously acknowledged. Here, we therefore review and summarize the relevant literature, quantifying the extent of sex-bias in intersexual dominance relations documented in observational and experimental studies in captivity and the wild. Female dominance is often, but not always, implemented by spontaneous male submission in the absence of female aggression and linked to female sexual maturation. We connect the available evidence to the hypotheses that have been proposed to explain the evolution of female dominance among lemurs. The occurrence of female dominance in all lemur families and the interspecific variation in its extent indicate that it has evolved soon after lemurs colonized Madagascar – presumably in response to particular ecological challenges – and that it has since been reduced in magnitude independently in some taxa. Our study contributes important comparative information on sex roles from an independent primate radiation and provides general insights into the conditions, opportunities and obstacles in the evolution of female-biased power.
... Any number of asymmetries beyond the obvious one in fighting ability can result in a power differential, including knowledge, relatedness or dependency. Some bases of power, such as control over mating opportunities and a skewed sex ratio, can be particularly important for understanding intersexual power [18,21,22,24] and some bases may be most relevant in humans. Irrespective of the base of power, individuals can accomplish power by various means, including aggression, noncompliance, a reward or even pheromones. ...
... Lastly, terms such as 'aggressive interaction' or 'agonistic interaction', for example, are preferred over 'dominance interaction' because they describe the encounter and do not preclude the role of leverage. For instance, in sifaka, sexually monomorphic lemurs where females have leverage in intersexual dyads, females often use the means of aggression towards males to get priority access to resources [24]. When conflicts arise over a prized food item (e.g. ...
... Instead, aggression may be more indicative of a power relationship that is uncertain [14,49] than of the presence of power, and may be more common during the formation of a relationship because this phase is a period of uncertainty rather than an association between rank and aggression [49]. When relationships are characterized by high certainty, the more powerful individual (whether due to dominance or leverage) may be able to evoke avoidance, cowering or a flee, for example, without aggression, such as in feral dogs [49], sifaka [24] and macaques [33,59]. The ability to evoke submission without exerting any energy could have fitness advantages over means, such as aggression, that expend energy and have a greater probability of resulting in injury. ...
Thorlief Schjelderup-Ebbe's seminal paper on the ‘pecking’ order of chickens inspired numerous ethologists to research and debate the phenomenon of dominance. The expansion of dominance to the broader concept of power facilitated disentangling aggression, strength, rank and power. Aggression is only one means of coercing other individuals, and can sometimes highlight a lack of power. The fitness advantages of aggression may only outweigh the costs during periods of uncertainty. Effective instruments of power also include incentives and refusals to act. Moreover, the stability of the power relationship might vary with the instruments used if different means of power vary in the number and types of outcomes achieved, as well as the speed of accomplishing those outcomes. In well-established relationships, actions or physiological responses in the subordinate individual may even be the only indicator of a power differential. A focus on strength, aggression and fighting provides an incomplete understanding of the power landscape that individuals actually experience. Multiple methods for constructing hierarchies exist but greater attention to the implications of the types of data used in these constructions is needed. Many shifts in our understanding of power were foreshadowed in Schjelderup-Ebbe's discussion about deviations from the linear hierarchy in chickens.
This article is part of the theme issue ‘The centennial of the pecking order: current state and future prospects for the study of dominance hierarchies’.
... Sex-depended differences in growth rates or body size may impose different energetic requirements on individuals. However, Verreaux's sifakas lack sexual dimorphism and males and females have similar body sizes and growth rates (Kappeler, 1991;Kappeler and Fichtel, 2012;Voyt et al., 2019), indicating that other factors drive the different age-fGCM relationships in females and males. ...
Glucocorticoids have wide-ranging effects on animals' behaviour, but many of these effects remain poorly understood because numerous confounding factors have often been neglected in previous studies. Here, we present data from a 2-year study of 7 groups of wild Verreaux's sifakas (Propithecus verreauxi), in which we examined concentrations of faecal glucocorticoid metabolites (fGCMs, n = 2350 samples) simultaneously in relation to ambient temperatures, food intake, rank, reproduction, adult sex ratios, social interactions, vigilance and self-scratching. Multi-variate analyses revealed that fGCM concentrations were positively correlated with increases in daily temperature fluctuations and tended to decrease with increasing fruit intake. fGCM concentrations increased when males were sexually mature and began to disperse, and dominant males had higher fGCM concentrations than subordinate males. In contrast to males, older females showed a non-significant trend to have lower fGCM levels, potentially reflecting differences in male and female life-history strategies. Reproducing females had the highest fGCM concentrations during late gestation and had higher fGCM levels than non-reproducing females, except during early lactation. Variation in fGCM concentrations was not associated with variation in social interactions, adult sex ratios, vigilance and self-scratching. Altogether, we show that measures of glucocorticoid output constitute appropriate tools for studying energetic burdens of ecological and reproductive challenges. However, they seem to be insufficient indicators for immediate endocrinological responses to social and nonsocial behaviours that are not directly linked to energy metabolism.
... Despite occurring at higher levels, male participation did not predict the outcome of intergroup encounters. Perhaps males were not particularly effective at supplanting other groups because they are 1) the same size or slightly smaller than females (Lewis and Kappeler 2005) and 2) subordinate to all adult females (Lewis 2006;Richard 1978;Richard and Nicoll 1987;Voyt et al. 2019). Instead, male participation may only be effective against extragroup males or as a supplement to female participation when residing in small groups. ...
... Verreaux's sifaka intergroup encounters appear to be long enough to allow individuals to decide whether to participate based on the behavior of others. Males, which are subordinate to females in sifaka societies (Lewis 2006;Richard 1978;Richard and Nicholl 1987;Voyt et al. 2019), participated in nearly all intergroup encounters, whereas females participated in only about half as often as males. Future research should examine the timing of participation in intergroup conflicts in sifaka. ...
Socioecological theory predicts that larger groups are able to gain better access to resources because of their numerical advantage in intergroup contests. Nevertheless, the numerical superiority hypothesis has received mixed support, perhaps due to the collective action problem and sex differences in strategies and payoffs. We tested the numerical superiority and the collective action problem hypotheses using 141 inter-group encounters in a 7-year dataset on 5 groups of Verreaux's sifaka (Propithecus verreauxi) at Ankoatsifaka Research Station in Kirindy Mitea National Park in western Madagascar. Contrary to the numerical superiority hypothesis, larger groups were not more likely to supplant smaller groups, nor was success determined by participation of a larger number of one sex. Consistent with a collective action problem, group size negatively affected participation. Notably, the sexes differed in which factors predicted individual participation. Male participation, which may serve to defend mating opportunities with resident females and signal competitive ability to neighboring groups, was greater than female participation, though we did not detect any strong predictor of male participation. Female participation was more likely during the lactation season, when food resources were scarce, than during the mating season. Contrary to previous studies, which argued that mothers with infants avoid intergroup conflicts because of the risk of infanticide, our study suggests that maternal energetic stress due to lactation and food scarcity increases the benefits of defending resources and instead drives mothers to participate in intergroup encounters. Thus, individual reproductive payoffs provide the private incentives needed to induce collective action.
... Specific patterns of intersexual power have also been attributed to sex ratio [3,9], seasonality [9,11], energetic costs [12], selection for deferential mates [10,11,13,14], intersexual differences in social support [15,16], winner-loser effects [17], and frequent intersexual interactions [18]. Intersexual power can also arise due to female control over reproduction [19,20] and the supply and demand (i.e., market effects [21]) of reproductive opportunities [2,3]. ...
... When factors favor the evolution of larger male body size (e.g., male-male contest competition for mates), the downstream effect is a constraint on the opportunities for female-biased power structures to evolve. When males are not substantially larger than females, female leverage can arise due to market effects [2,21] or asymmetry between the sexes in resource value [20,100,101]. In primates, more variables appear to favor male-biased power than female-biased power ( Figure 4). ...
Dominance and leverage are both possible causes of social inequality. If sexual dimorphism influences patterns of intersexual dominance, we predicted that highly dimorphic species are constrained to exhibit male-biased power (MP), but species with low sexual dimorphism are free to demonstrate a broader range of intersexual power relationships. If market effects influence intersexual leverage, we predicted that females have more power when group composition is more male-biased and estrus is asynchronous. We analyzed data on intersexual power, sexual dimorphism, expected estrous overlap, and sex ratio for 79 extant primate species using phylogenetic logistic regression and ancestral state reconstructions. Although MP is more common, every major primate clade includes non-MP species. MP was associated with greater body mass and canine length dimorphism and with female-biased sex-ratios. Low estrous overlap was associated with non-MP. Although MP was reconstructed as likely ancestral for anthropoids, the last common ancestor of this clade probably did not exhibit high sexual dimorphism. The last common ancestor of catarrhines was probably highly dimorphic, potentially constraining intersexual power relationships. Non-MP probably evolved multiple times in primates and may be less common because multiple traits are linked to MP while fewer traits are associated with female-biased power or equality.
Female dominance is often associated with lemurs. However, consensus does not exist among primatologists on how to define, measure, or explain female dominance. This review explores the utility of applying a broader concept of power to understanding lemur intersexual relationships. In this framework, power is defined as arising from an asymmetry in a dyadic relationship and can be divided into 2 types: dominance and leverage. Intersexual asymmetries based upon females having superior fighting ability are considered female dominance. However, economic power also exists, and females with resource-based power exhibit female leverage. Additionally, power has 4 characteristics (base, means, amount, and scope) that describe the precise nature of observed phenomena. This article utilizes the 4 characteristics outlined in the power framework to review the existing “female dominance” literature for lemurs and highlights the value of adopting both an expanded concept of power and a more precise language. By placing the multiple phenomena currently labeled under the single term “female dominance” within the power framework, much of the confusion disappears. Thus, not only is the debate reframed, facilitating endeavors to find evolutionary explanations, but the uniqueness of female power in lemurs can be determined empirically rather than by definition.
