Assessment during aggressive contests between male jumping spiders

Assessment strategies are an important component in game theoretical models of contests. Strategies can be either based on one's own abilities (self-assessment) or on the relative abilities of two opponents (mutual assessment). Using statistical methodology that allows discrimination between assessment types, we examined contests in the jumping spider Phidippus clarus. In this species, aggressive interactions can be divided into ‘precontact’ and ‘contact’ phases. Precontact phases consist of bouts of visual and vibratory signalling. Contact phases follow where males physically contact each other (leg fencing). Both weight and vibratory signalling differences predicted winners, with heavier and more actively signalling males winning more contests. Vibratory behaviour predicted precontact phase duration, with higher signalling rates and larger differences between contestants leading to longer precontact interaction times. Contact phase duration was predicted most strongly by the weight of losing males relative to that of winning males, suggesting that P. clarus males use self-assessment in determining contest duration. While a self-assessment strategy was supported, our results suggest a secondary role for mutual assessment (‘partial mutual assessment’). After initial contest bouts, male competitors changed their behaviour. Precontact and contact phase durations were reduced while vibratory signalling behaviour in winners was unchanged. In addition, only vibratory signalling differences predicted winners in subsequent bouts, suggesting a role of experience in determining contest outcomes. We suggest that the rules and assessment strategies that males use can change depending on experience and that assessment strategies are probably a continuum between self-assessment and mutual assessment.