Data from: Condition-dependent trade-off between weapon size and immunity in males of the European earwig

Investigating the expression of trade-offs between key life-history functions is central to our understanding of how these functions evolved and are maintained. However, detecting trade-offs can be challenging due to variation in resource availability, which masks trade-offs at the population level. Here, we investigated in the European earwig Forficula auricularia whether (1) weapon size trades off with three key immune parameters – hemocyte concentration, phenoloxidase and prophenoloxidase activity - and whether (2) expression and strength of these trade-offs depend on male body condition (body size) and/or change after an immune challenge. Our results partially confirmed condition dependent trade-offs between weapon size and immunity in male earwigs. Specifically, we found that after an immune challenge, weapon size trades off with hemocyte concentrations in low-condition, but not in good-condition males. Contrastingly, weapon size was independent of pre-challenge hemocyte concentration. We also found no trade-off between weapon size and phenoloxidase activity, independent of body condition and immune challenge. Overall, our study reveals that trade-offs with sexual traits may weaken or disappear in good-condition individuals. Given the importance of weapon size for male reproductive success, our results highlight how low-condition individuals may employ alternative life-history investment strategies to cope with resource limitation.探究关键生活史功能间的权衡（trade-offs）表达，是我们理解这些功能如何演化并得以维持的核心所在。然而，资源可获得性的变异会掩盖种群水平的权衡现象，使得权衡关系的检测颇具挑战。本研究以欧洲球螋（Forficula auricularia）为实验对象，探究了两个问题：其一，雄性的武器大小是否与三项关键免疫参数——血细胞浓度（hemocyte concentration）、酚氧化酶（phenoloxidase）活性及酚氧化酶原（prophenoloxidase）活性——存在权衡；其二，这些权衡的表达与强度是否依赖于雄性身体状态（体型），抑或会在免疫刺激（immune challenge）后发生改变。研究结果部分证实了雄性球螋的武器大小与免疫功能间存在依赖于身体状态的权衡关系。具体而言，在经历免疫刺激后，低身体状态的雄性个体中，武器大小与血细胞浓度呈权衡关系，而高身体状态的雄性个体中则未观察到此现象。与之相反，免疫刺激前的血细胞浓度与武器大小并无关联。此外，无论身体状态与免疫刺激情况如何，武器大小与酚氧化酶活性均未表现出权衡关系。总体而言，本研究揭示，与性征相关的权衡关系可能在高身体状态的个体中减弱甚至消失。鉴于武器大小对雄性繁殖成功率的重要性，本研究结果凸显了低身体状态个体可能采用替代性生活史投资策略，以应对资源限制。