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, while 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. Using the insect, Narnia femorata (Hemiptera: Coreidae), an insect where males use their hind legs as weapons and the femurs are enlarged, we studied 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, while 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）在种群内的体型往往存在高度变异，这与其与个体生理状态的紧密关联直接相关。营养状况对个体生理状态具有显著影响，因此理论上，营养质量的季节性变化，会同时改变种群中性选择性状的平均体型与性二态性（sexual dimorphism）程度。尽管受配偶选择影响的性状已得到充分研究，但令人惊讶的是，我们对自然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，仍知之甚少。此外，鲜有研究明确检验不同营养环境下，性选择性状的遗传力（heritability）与均值尺度演化潜力（evolvability）的差异。本研究以足缘蝽*Narnia femorata*（半翅目：缘蝽科，Hemiptera: Coreidae）为实验材料——该物种雄性以后足作为格斗武器，且股骨膨大——我们探究了在野外实际存在的营养梯度下，武器表达、性二态性以及演化潜力的变化幅度。研究发现，取食低质量饲料（无果实的仙人掌）的种群几乎呈单态性，而取食高质量饲料（带成熟果实的仙人掌）的种群，则因雄性拥有发达的后足武器，呈现出显著的性二态性。与我们的预期相反，我们未在所检测的任何性状中发现演化改变的潜力。因此，尽管本研究证实性选择武器高度依赖个体生理状态，且武器表达与二态性的变化可能改变种群演化动态，但当前环境下，该实验种群不太可能发生进一步的演化改变。