Aggressiveness and submissiveness in spotted hyaenas: one trait or two?

Abstract

Aggressive and submissive behaviours are commonly assumed to represent two extremes of a single personality trait, often labelled ‘aggressiveness’. However, most studies focus exclusively on submissive behaviour elicited by conspecific aggression, and on rates at which aggressive and submissive behaviours are expressed, without considering either unprovoked submissive behaviour, or the intensity of the actions themselves. Utilizing a long-term data set spanning 27 years of dyadic agonistic interactions among spotted hyaenas, Crocuta crocuta , including counts and intensities of all unprovoked acts of aggressive and submissive behaviour, we assessed consistency within individuals in these behaviours. We found that counts of acts of both aggression and submission performed by adult female hyaenas varied with context, that neither measure was consistent within individuals over time and that both were strongly affected by social rank, suggesting that neither of these rate measures represent personality traits. Although rank influenced the intensity of submissive acts, intensity of aggressive acts did not vary with rank. Intensities of aggressive and submissive acts also varied with context, but both were consistent within individual females regardless of age, suggesting that both intensity measures may represent personality traits. We found no significant correlation between individual lifetime averages of intensities of aggressive and submissive behaviour, supporting the hypothesis that these may represent different traits rather than opposite ends of a single spectrum. Lifetime rates at which females performed acts of aggression and submission were uncorrelated with fitness, but analysis of the average intensity of aggressive or submissive acts performed by adult female hyaenas suggests that lifetime reproductive success may be lower at both ends of the spectrum of behavioural intensity than in its centre after controlling for rank, suggesting the action of stabilizing selection. • Hyaenas showed individual consistency in aggressive and submissive behaviours. • Aggressive/submissive personality traits were not correlated within individuals. • Individual fitness was loosely correlated with the intensity of such behavioural acts. • Rank significantly influenced the frequency of behavioural acts expressed. • Hyaenas showing very high or low agonistic intensity had lower offspring survival.