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...

适存条件（Condition）被定义为个体可分配至提升适合度性状（fitness-enhancing traits）的资源总量。因此，若存在发育权衡（developmental trade-offs），适存条件或可对其产生调控作用。尽管已有诸多研究通过调控膳食条件验证了条件依赖型性状表达（condition-dependent trait expression），但鲜有研究明确特定营养物质对适存条件或发育权衡的具体贡献。本研究借助营养几何学（nutritional geometry），量化了膳食蛋白质与碳水化合物含量对幼虫生长表现的影响，以及对雄性宽角甲虫（broad-horned beetles）Gnatocerus cornutus成虫形态发育的调控作用，其中形态指标涵盖体型大小，以及该物种的一级与二级性选择性状（sexually selected trait）。研究结果显示，子代存活率、发育速率与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。其中，二级性征（secondary sexual character）的绝对大小——大颚（mandibles）……