The winner and loser effect: What fighting behaviours are influenced?

We examined the effect of prior winning and losing experiences on the initi ating and responding strategies of contestants in contests between individu als of Rivulus marmoratus (Cyprinodontidae). Each contestant tvas given a p enultimate and a recent fighting experience approximately 48 and 24 h prior to the dyadic contests, respectively, through randomly selected procedures . Winning and losing experience appeared to influence different types of fi ghting behaviours. Losing: experiences decreased the probability of an indi vidual initiating a confrontation and thus increased its tendency to retrea t immediately when challenged. Winning experiences did not affect the proba bility of initiation, but significantly increased the likelihood of an indi vidual initiating with attacks that effectively deterred its opponents. A s ubstantial proportion (59/153) of individuals retreated immediately when ch allenged and reduced the number of fights available for examining experienc e effects on responding strategies at later stages of a contest. None the l ess, winning experiences consistently increased the likelihood of an indivi dual retaliating by attacking its opponent at various stages of a contest, and eventually increased its probability of escalating a confrontation into physical fights. However, the effects of losing experiences on these respo nding strategies were undetectable. Recent experiences significantly affect ed all fighting behaviours examined, but penultimate experiences significan tly affected only the tendency to initiate a confrontation with attacks and the likelihood of escalation. These results indicated that prior experienc es had the longest lasting effect on the potentially most costly fighting b ehaviour. Prior experiences influenced the outcome of nonescalated contests as well as the probability of escalation, but did not significantly affect the outcome of escalated contests. These results are consistent with the h ypothesis that prior experiences modify the information that an individual has. about its fighting ability but do not alter its actual fighting abilit y and that actual fighting ability becomes the more important influence on outcomes of escalated contests. (C) 2001 The Association for the Study of A nimal Behaviour.