Hierarchical steepness, counter-aggression, and macaque social style scale

Area of Science:

• Primatology
• Behavioral Ecology
• Evolutionary Biology

Background:

• Nonhuman primates, particularly macaques (genus Macaca), exhibit significant diversity in social structures.
• Social style, characterized by covarying social traits, offers a framework to understand this variation.
• Macaque species are often categorized on a four-grade scale from despotic (grade 1) to tolerant (grade 4).

Purpose of the Study:

• To assess how dominance gradients (hierarchical steepness) and counter-aggression fit the macaque social style scale.
• To investigate the influence of phylogenetic relationships on observed correlations between social traits and the social style scale.
• To determine if evolutionary changes in social style are directional or influenced by phylogenetic relatedness.

Main Methods:

• Quantified dominance gradients and counter-aggression in macaque species.
• Mapped these behavioral measures onto phylogenetic trees.
• Utilized independent contrasts to analyze evolutionary changes and correlations with the social style scale, controlling for phylogeny.

Main Results:

• Raw scores for steepness and counter-aggression correlated with the social scale, but distributions varied by measure.
• Counter-aggression showed a dichotomous pattern (grade 4 distinct), while steepness appeared more continuous.
• Extreme grades (1 and 4) were distinct, but intermediate grades showed inconsistent variation.
• Phylogenetic analysis indicated that correlations with the social scale are largely attributable to species' relatedness, not necessarily direct evolutionary adaptation of social style.

Conclusions:

• Covariation in social traits is more apparent between extreme social styles (despotic vs. tolerant) than intermediate ones.
• Phylogenetic relationships significantly influence the observed correlations between social traits and the social style scale in macaques.
• The observed patterns suggest that shared ancestry, potentially due to past ecological adaptations or simply phylogenetic closeness, plays a key role in shaping macaque social structures.