Data from: Experimental manipulation reveals a trade-off between weapons and testes

Theory predicts a trade-off between sexually-selected weapons used to secure mates and post-copulatory traits used to maximize fertilization success. However, individuals that have a greater capacity to acquire resources from the environment may invest more in both pre- and post-copulatory traits, and trade-offs may not be readily apparent. Here, we manipulate the phenotype of developing individuals to examine allocation trade-offs between weapons and testes in Mictis profana (Hemiptera: Coreidae), a species where the hind legs are sexually selected weapons used in contests over access to females. We experimentally prevented males from developing weapons by inducing them to autotomize their hind legs before the final molt to adulthood. We compared trait expression in this group to males where autotomy was induced in the mid legs, which are presumably not under sexual selection to the same extent. We found males without weapons invested proportionally more in testes mass than those with their mid legs removed. Males that developed to adulthood without weapons did not differ from the mid leg removal group in other traits potentially under pre-copulatory sexual selection, other post-copulatory traits, or naturally selected traits. In addition, a sample of adult males from the same population in the wild revealed a positive correlation between investment in testes and weapons. Our study presents a critical contribution to a growing body of literature suggesting the allocation of resources to pre- and post-copulatory sexual traits is influenced by a resource allocation trade-off and that this trade-off may only be revealed with experimental manipulation.

理论预测，用于求偶竞争的性选择武器（sexually-selected weapons）与用于最大化受精成功率的交配后性状（post-copulatory traits）之间存在资源分配权衡。然而，环境资源获取能力更强的个体，可能同时在交配前性状（pre-copulatory traits）和交配后性状上投入更多资源，因此这类权衡往往不易被直观观测到。本研究通过操控发育个体的表型，探究异背长蝽（Mictis profana，半翅目（Hemiptera）：缘蝽科（Coreidae））的性选择武器与精巢间的资源分配权衡。该物种的后足为用于争夺雌性交配权的性选择武器。我们通过诱导雄性个体在末次蜕皮至成虫阶段前自切后足，使其无法发育出性选择武器。我们将该组雄性的性状表达水平，与另一组诱导自切中足的雄性进行比较——中足通常不会受到同等程度的性选择压力。结果显示，未发育出性选择武器的雄性，其精巢质量相对投入量显著高于中足被自切的雄性。未发育出性选择武器的雄性成虫，在其他潜在受交配前性选择、交配后性状或自然选择的性状上，与中足自切组雄性均无显著差异。此外，对同一野生种群的成年雄性样本进行检测后发现，精巢投入与性选择武器投入之间呈显著正相关。本研究为日益增长的相关学术文献提供了关键证据：交配前与交配后性性状的资源分配确实受资源权衡机制调控，且这类权衡仅能通过实验操控得以揭示。