Rival assessment and comparison of morphological and performance-based predictors of fighting ability in Lake Eyre dragon lizards, Ctenophorus maculosus

Abstract

Although the outcome of contests is often critical to fitness, we still have much to learn regarding the reliability of different predictors of fighting ability (e.g. morphological traits versus performance measures) and the strategies individuals use to decide when to withdraw. We examined predictors of contest success and assessment strategies in staged contests between male Lake Eyre dragon lizards, Ctenophorus maculosus, in which males engage in escalated contests. Bite force was the only significant predictor of contest success. Although head width and depth predicted the number and duration of bites during contests, neither of these traits predicted contest outcome, nor did body size or experience in the prior two contests. These results support the view that measures of physical performance may be more reliable indicators of male fighting ability in escalated contests than morphological traits, because performance is more directly linked to the quality being signalled (i.e. fighting ability). Contest intensity was positively associated with the resource holding potential (RHP) of the loser, but not that of the winner or RHP asymmetry, indicating that individuals base their decision to withdraw on assessment of their own cost threshold (self-assessment) rather than assessment of their opponent’s ability (mutual assessment). Lastly, the number of displays (head bobs and push-ups) was also correlated with the RHP of losers (but not winners or RHP asymmetry), consistent with the recently proposed ‘information conflict hypothesis’, which predicts that weaker individuals should limit information transfer about their ability by performing fewer displays.