Data from: The tale of the shrinking weapon: seasonal changes in nutrition affect weapon size and sexual dimorphism, but not contemporary evolution

Sexually selected traits are often highly variable in size within populations due to their close link with the physical condition of individuals. Nutrition has a large impact on physical condition, and thus, any seasonal changes in nutritional quality are predicted to alter the average size of sexually selected traits as well as the degree of sexual dimorphism in populations. However, although traits affected by mate choice are well studied, we have a surprising lack of knowledge of how natural variation in nutrition affects the expression of sexually selected weapons and sexual dimorphism. Further, few studies explicitly test for differences in the heritability and mean-scaled evolvability of sexually selected traits across conditions. We studied Narnia femorata (Hemiptera: Coreidae), an insect where males use their hind legs as weapons and the femurs are enlarged, to understand the extent to which weapon expression, sexual dimorphism and evolvability change across the actual range of nutrition available in the wild. We found that insects raised on a poor diet (cactus without fruit) are nearly monomorphic, whereas those raised on a high-quality diet (cactus with ripe fruit) are distinctly sexually dimorphic via the expression of large hind leg weapons in males. Contrary to our expectations, we found little evidence of a potential for evolutionary change for any trait measured. Thus, although we show weapons are highly condition dependent, and changes in weapon expression and dimorphism could alter evolutionary dynamics, our populations are unlikely to experience further evolutionary changes under current conditions.

性选择性状（sexually selected traits）在种群内的个体间通常存在高度体型变异，这是因为其与个体的身体状况紧密相关。营养状况对个体身体状况影响显著，因此理论上，营养质量的季节性变化会改变种群中性选择性状的平均体型，以及种群内的性二态性（sexual dimorphism）程度。然而，尽管受配偶选择影响的性状已得到充分研究，但我们对自然状态下的营养变异如何影响性选择武器（sexually selected weapons）的表达以及性二态性，仍存在令人意外的认知空白。此外，鲜有研究明确检验不同环境条件下，性选择性状的遗传力（heritability）与均值尺度下的可进化性（evolvability）之间的差异。本研究以半翅目缘蝽科的足丝缘蝽（Narnia femorata）为研究对象——该物种的雄性以后足作为武器，且腿节膨大——旨在探究在野外实际存在的营养梯度范围内，武器表达、性二态性以及可进化性的变化幅度。研究结果显示，喂食低营养日粮（无果实的仙人掌）的个体几乎呈单态，而喂食高质量日粮（带有成熟果实的仙人掌）的个体则因雄性表达发达的后足武器，呈现出显著的性二态性。与研究预期相悖的是，本研究未发现被测性状存在进化改变的潜在可能。因此，尽管本研究证实性选择武器高度依赖个体身体状况，且武器表达与二态性的变化可能改变进化动态，但当前环境下，研究种群不太可能发生进一步的进化改变。