Sex and dominance: How to assess and interpret intersexual dominance relationships in mammalian societies

Abstract

The causes and consequences of being in a particular dominance position have been illuminated in various animal species, and new methods to assess dominance relationships and to describe the structure of dominance hierarchies have been developed in recent years. Most research has focused on same-sex relationships, however, so that intersexual dominance relationships and hierarchies including both sexes have remained much less studied. In particular, different methods continue to be employed to rank males and females along a dominance hierarchy, and sex biases in dominance are still widely regarded as simple byproducts of sexual size dimorphism. However, males and females regularly compete over similar resources when living in the same group, and sexual conflict takes a variety of forms across societies. These processes affect the fitness of both sexes, and are mitigated by intersexual hierarchies. In this study, we draw on data from free-ranging populations of nine species of mammals that vary in the degree to which members of one sex dominate members of the other sex to explore the consequences of using different criteria and procedures for describing intra- and intersexual dominance relationships in these societies. Our analyses confirmed a continuum in patterns of intersexual dominance, from strictly male-dominated species to strictly female-dominated species. All indices of the degree of female dominance were well correlated with each other. The rank order among same-sex individuals was highly correlated between the intra- and intersexual hierarchies, and such correlation was not affected by the degree of female dominance. The relative prevalence of aggression and submission was sensitive to variation in the degree of female dominance across species, with more submissive signals and fewer aggressive acts being used in societies where female dominance prevails. Thus, this study provides important insights and key methodological tools to study intersexual dominance relationships in mammals.

Loquens : A characterization of “Hunter-Gatherers of Words”

“…Prevalence of specific dominance patterns in the dispersing group may also have played a role. There is evidence for fewer aggressive acts being used in societies where female dominance prevails (Kappeler et al, 2022;Davidian et al, 2022), as a result of sex differences in reactive aggression (Aubry et al, 2022). This line of thought would fit well with reverse dominance patterns hypothesized by Knight et al (1995); Knight (2010), building on Boesch (2009), to account for the earliest functions of ochre-based symbols in our lineage (Potts et al, 2018(Potts et al, , 2020.…”

How to measure intersexual dominance?

“…In DomWorld, intrasexual dominance hierarchies were more accurate when hierarchies were built using outcomes from conflicts among all adults as opposed to just intrasexual conflicts. In line with this, an empirical study has shown that the location of individuals in a hierarchy based on same-sex conflicts correlated strongly with their location in the hierarchy based on conflicts among all adults, suggesting the two hierarchies are highly related (Kappeler et al, 2022b). Thus, we propose that when studying intrasexual dominance, intersexual conflicts should also be considered because they may induce winner-loser effects which influence an individual's ability to win intrasexual conflicts, and their inclusion may make intrasexual hierarchies more accurate.…”

“…Yet, intersexual dominance in a group is seldom binary. Rather, groups may range from strongly male-dominant to strongly femaledominant (Davidian et al, 2022;Kappeler et al, 2022b). For instance, strict female dominance over males was supposed to be widespread in lemurs, but intersexual dominance relations have been shown to vary across groups and species, when they were measured as the proportion of intersexual conflicts won and the proportion of subordinate males (Kappeler et al, 2022a).…”

“…What remains unclear is which measure of intersexual dominance best represents dominance relations between the sexes in groups of animals. A study by Kappeler et al (2022b) demonstrated that the degree of intersexual dominance strongly correlated among several measures of it, suggesting that all measures were equally suitable. However, in empirical studies, the accuracy of measures cannot be determined because there is no "true" value of intersexual dominance with which the degree of intersexual dominance based on observed conflicts can be compared.…”

Male intrasexual aggression and partial dominance of females over males in vervet monkeys

“…It should be noted that in multiple species (among which vervet monkeys) the rank order of same sex individuals was highly correlated between dominance hierarchies based on TABLE 1 Information on groups per year (in parentheses) regarding the number (#) of adults of each sex, the proportion of males, the number of dyadic fights, the degree of female dominance (i.e., Female Dominance Index) from dyadic interactions and when interactions with support were added to the calculation of the dominance hierarchy, and the steepness of the hierarchy of all adults and of males only. interactions among the same sex only and on among both sexes (Kappeler et al, 2022). When only a single male was present in a group, it was impossible to calculate the steepness of the hierarchy among males and therefore, this group-year point was excluded from the analyses (so, four group-year points were excluded).…”