Fighting isn't sexy in lekking greater sage-grouse: a relational event model approach for mating interactions

The relationship between aggression and mate choice in mating systems is critical for understanding the evolution and diversification of sexual organisms and yet remains the subject of vigorous debate. A key challenge is that traditional correlational approaches cannot distinguish underlying mechanisms of social interaction and can indicate misleading positive associations between aggression and mating events. We implement a novel relational event model (REM) incorporating temporal dependencies of events in a social network to study natural reproductive behaviour in a lek-breeding system where males gather to display and females visit to evaluate mates, often observing both male courtship displays and fights. We find that fighting is not attractive to females. Indeed, males are less likely to start and more likely to leave fights with females present, plausibly to avoid entanglement in protracted combat cycles arising from emergent social processes that reduce availability to mate. However, fighting serves other roles, e.g. to deter copulation interruptions and rebuff competitors. Our findings support the hypothesis that social systems regulating conflict and promoting females' choice based on display are fundamental to stable lek evolution. Moreover, our analysis highlights the utility of the REM framework in testing mechanistic hypotheses in behavioural ecology and evolution.