Assessment of self, opponent and resource during male–male contests in the sierra dome spider, Neriene litigiosa: Linyphiidae

Contestants in agonistic encounters may use assessments of self, opponent and resource quality as a basis for making behavioural decisions. Ritualized displays reduce risk and energy expenditure during assessments, but may lead to injurious fighting behaviour under certain circumstances. In this study, we examined the decision-making process of male sierra dome spiders (Neriene (=Linyphia) litigiosa: Linyphiidae) during 323 male–male contests using multivariate analysis. In contests over females, male ritualized displays include distinct phases by which males facultatively escalate fights: ritualized noncontact display, pedipalp wrestling, and unritualized biting and grappling. Amongst these phases we found evidence for all three types of assessment. Self-assessment was indicated by effects of the lighter male’s mass and the metabolic effect of temperature. These factors influenced the duration of noncontact display, likelihood of escalation and energetic expenditures. Opponent assessment, indicated by the effects of the difference in mass between contestants, influenced all aspects of fight behaviour when differences in body mass were large. When differences in body mass were small, relative mass only affected the duration of the fight, primarily by lengthening noncontact display. Resource assessment, measured through effects of female reproductive value and the males’ future reproductive opportunities, primarily influenced the decision to escalate to unritualized combat and the duration of the unritualized combat. Our multivariate analysis of behaviourally distinct phases of contests showed that contestants use diverse information to adjust investment in displays and potentially injurious fighting. We discuss the roles of information transfer versus raw attempts to influence outcomes in this complex contest system.