Sexually selected traits, including threat signals, have been shown to scale steeply positively with body size because their exaggeration maximizes honest signalling. However, the functional allometry hypothesis makes the opposite prediction for some weapons: because the biomechanics of force applied in their use may favor relatively smaller size, sexually selected weapons may exhibit negative allometry. Tests of these ideas in insects have largely focused on holometabolous species, whose adult body size is entirely dependent on nutrients acquired during the larval stage. In contrast, hemimetabolous insects may exhibit different patterns of allometry development because they forage throughout development, between successive moults. Here, we tested complementary and competing predictions made by the positive and functional allometry hypotheses, regarding intrasexually selected trait allometry in a hemimetabolous insect, the Jamaican field cricket (Gryllus assimilis). As expected, head width (a dominance and/or combat trait) was more positively allometric than non-sexually selected traits. In contrast, and consistent with the functional allometry hypothesis, mouthparts (weapons) were either isometric or negatively allometric. We also tested whether trait allometry responded to rearing diet by raising males on either a high protein diet or a high carbohydrate diet; we predicted stronger positive allometry under the high protein diet. However, diet did not influence allometry in the predicted manner. Overall, our results support the functional allometry hypothesis regarding sexually selected trait allometry and raise intriguing possibilities for integrating these ideas with recent paradigms for classifying intrasexually selected traits.

性选择的特征，包括威胁信号，已经显示出与体型成正比，因为它们的夸张可以使诚实的信号最大化。但是，功能性变态假说对某些武器做出了相反的预测：由于在使用武器时使用的生物力学力可能偏向于相对较小的尺寸，因此按性别选择的武器可能表现出负性变态。在昆虫中对这些想法的测试主要集中在同代谢物种上，其成年体的大小完全取决于幼体阶段获得的营养。相比之下，半代谢昆虫可能表现出不同的异速生长发育模式，因为它们在连续换羽期之间的整个发育过程中进行觅食。在这里，我们测试了基于积极和功能性异构假设的互补性和竞争性预测，Gryllus assimilis）。不出所料，头部宽度（主导和/或战斗特质）比非性行为特长具有更好的异向性。相反，与功能性异体假说相符的是，口器（武器）是等长或负等长的。我们还测试了性状异位症是否通过饲喂高蛋白饮食或高碳水化合物饮食的雄性来响应饲养饮食；我们预测在高蛋白饮食下更强的正异体感。但是，饮食并未以预期的方式影响异速症。总体而言，我们的研究结果支持有关性选择特征异向性表达的功能性异同假设，并为将这些思想与对性别选择的性状进行分类的最新范式整合提供了有趣的可能性。