Fixed or flexible? Winner/loser effects vary with habitat quality in a parasitoid wasp

Abstract

Prior experience of fighting affects the outcome of subsequent contests, with prior winners being more likely to win and prior losers being more likely to lose a future encounter. These winner and loser effects have been shown in numerous species but have usually been tested in only one set of conditions. However, if such effects are not fixed but context dependent, we can expect their strength to change according to the situation. In particular, their magnitude could covary with other factors, such as those influencing contestants’ fighting abilities or the value they place on the contested resource, which in turn are known to influence contest behaviors and outcomes. Here, we tested the effect that prior experience of resource availability had on the expression of winner and loser effects in Eupelmus vuilleti, a parasitoid wasp fighting for hosts on which to lay their eggs. We showed that a loser effect was observable only when females experienced a habitat rich in hosts (hence placed low value on the contested individual host) but not when they were deprived of hosts (leading to individual hosts having high value). Contrary with a prior study, no clear winner effect was observed. These results suggest that the strength of winner and loser effects are context dependent in E. vuilleti, and interactions with other factors can either accentuate or attenuate the effects. Our data further raise the question of whether the intensity of the first encounter, not only its outcome, influences the behavioral decisions of individuals during a subsequent contest. A previous victory can increase the chance of winning a subsequent fight, while a prior defeat can increase the chance of losing. Such winner and loser effects have been shown in numerous species but have usually been studied in only one set of conditions. We show that the strength of these effects can be context dependent, such that they are accentuated or attenuated when experience interacts with factors such as habitat quality. Our data further raise the question of whether the intensity of the first encounter (how “hard” it was to win or lose), not just the outcome, influences behavioral decisions during subsequent contests.