Data from: Prior experience and contest outcome: winner effects persist in absence of evident loser effects in a parasitoid wasp

The experience of a prior conflict can affect animals' performance during a later contest: a victory usually increases while a defeat decreases the probability of winning a subsequent conflict. These winner and loser effects could result from a reassessment by contestants of their perceived fighting abilities. Game-theoretic models based on this assumption predict that a loser effect can exist alone or in the presence of a winner effect, but a winner effect cannot persist alone, at least when contestants are young and without experience of contest. Moreover, when both effects coexist, the loser effect is expected to be of a greater magnitude and last longer than the winner effect. To date, these predictions have been supported by empirical evidence. Here, we show for the first time that a winner effect can exist in the absence of any evident loser effect, in a parasitoid wasp, Eupelmus vuilleti, when fighting for hosts. It consequently raises questions about the possible mechanisms involved and challenges the main assumption of previous theoretical models. We suggest an alternative explanation for the evolution of only winner effects, based on the modification of contestants' subjective value of the resource rather than on a re-estimation of their fighting abilities.

过往的冲突经历会影响动物在后续争斗中的表现：获胜通常会提升后续争斗的获胜概率，而失败则会降低该概率。这类胜后效应（winner effect）与败后效应（loser effect），可能源于争斗个体对自身感知战斗能力的重新评估。基于该假设的博弈论模型预测，败后效应可单独存在，也可与胜后效应共存，但胜后效应无法单独存续——至少在争斗个体尚年轻且无争斗经历的情况下如此。此外，当两类效应共存时，败后效应的强度预计会大于胜后效应，且持续时间更久。迄今为止，上述预测均得到了实证证据的支持。本研究首次证实，在寄蜂（Eupelmus vuilleti）争夺寄主的争斗中，胜后效应可在无明显败后效应的情况下单独存在。这一发现随即引发了关于其潜在作用机制的疑问，并对以往理论模型的核心假设提出了挑战。我们基于争斗个体对资源主观价值的改变，而非对自身战斗能力的重新评估，为仅存在胜后效应的演化提出了一种替代性解释。