Data from: Macronutrient balance mediates the growth of sexually selected weapons but not genitalia in male broad-horned beetles

Condition is defined as the pool of resources available to an individual that can be allocated to fitness-enhancing traits. Consequently, condition could influence developmental trade-offs if any occur. Although many studies have manipulated diet to demonstrate condition-dependent trait expression, few studies have determined the contribution of specific nutrients to condition or trade-offs. We used nutritional geometry to quantify the effects of dietary protein and carbohydrate content on larval performance and the development of adult morphology including body size as well as a primary and secondary sexually selected trait in male broad-horned beetles, Gnatocerus cornutus. We found that offspring survival, development rate and morphological traits were highly affected by dietary carbohydrate content and to a lesser extent by protein content and that all traits were maximized at a protein-to-carbohydrate ratio around 1:2. The absolute size of a secondary sexual character, the mandibles, had a heightened response to the increased availability and ratio of both macronutrients. Male genitalia, in contrast, were relatively insensitive to the increased availability of macronutrients. Overall, while nutrition influenced trait expression, the nutritional requirements of development rate and morphological traits were largely the same and resource acquisition seems to implement only weak trade-offs in this species. This finding contrasts with some resource constraint predictions, as beetles seem able to simultaneously meet the nutritional requirements of most traits.

个体条件（Condition）被定义为个体可用于分配至提升适配度性状的可用资源池。因此，若存在发育权衡现象，个体条件可对其产生影响。尽管已有诸多研究通过调控饮食来验证条件依赖型性状表达，但鲜有研究明确特定营养物质对个体条件或发育权衡的贡献度。本研究采用营养几何学（nutritional geometry）方法，定量分析了膳食蛋白质与碳水化合物含量对雄性大角甲虫（Gnatocerus cornutus）幼虫存活表现以及成虫形态发育（包括体型大小）的影响，同时考察了该物种雄性的初级与次级性选择性状。研究结果显示，子代存活率、发育速率以及形态性状均受膳食碳水化合物含量的显著影响，受蛋白质含量的影响相对较弱；且所有性状均在蛋白质与碳水化合物比例约为1:2时达到最优值。次级性征——大颚——的绝对大小，对两种宏量营养素（macronutrients）的可获得性及其比例升高的响应更为显著。与之相反，雄性生殖器对宏量营养素可获得性的提升相对不敏感。总体而言，尽管营养物质会影响性状表达，但发育速率与形态性状的营养需求大体一致，且在该甲虫物种中，资源获取仅能引发较弱的发育权衡。该研究结果与部分资源限制预测相悖，因为此类甲虫似乎能够同时满足多数性状的营养需求。