Data from: Novel host plant leads to the loss of sexual dimorphism in a sexually-selected male weapon

In this time of massive global change, species are now frequently interacting with novel players. Greater insight into the impact of these novel interactions on traits linked to fitness is essential, because effects on these traits can hinder population existence or promote rapid adaptation. Sexually-selected weapons and ornaments frequently influence fitness and often have heightened condition-dependence in response to nutrition. Condition-dependence in response to different ecological conditions, a form of developmental plasticity, may be responsible for much of the intraspecific variation in sexually selected ornaments and weapons in wild populations. Here we examined the consequences of developing on a novel plant for the expression of size and shape in the leaf-footed cactus bug Narnia femorata (Hemiptera: Coreidae). The males of this species possess enlarged, sexually-dimorphic femurs on their hind legs. These legs are used as weapons in male-male contests. Females are typically larger in overall body size. Our study revealed that developing upon a novel host can lead to pronounced phenotypically plastic change in sexually-dimorphic traits. Male hind femurs were greatly impacted by the novel diet to the extent that the sexual dimorphism in hind femurs was lost. Further, dimorphism in body size increased, as males became tiny adults while females better maintained their body size. These patterns underscore the complex effects that novel species interactions may have on sexual phenotypes.在全球巨变的当下，各类物种正频繁与全新的交互对象产生互动。深入解析这些新型交互对与适合度（fitness）相关性状的影响至关重要，因为此类性状的变化可能阻碍种群存续，或是推动种群快速适应环境。经性选择演化出的武器与装饰性状，通常会对个体适合度产生显著影响，且往往会因营养状况变化而表现出更强的条件依赖性（condition-dependence）。针对不同生态条件的条件依赖性，作为发育可塑性（developmental plasticity）的一种表现形式，或许是野生种群中性选择相关的武器与装饰性状出现大量种内变异（intraspecific variation）的核心原因。本研究以叶足仙人掌蝽（*Narnia femorata*，半翅目：缘蝽科）为对象，探究了其在新型寄主植物上发育时，体型大小与形态特征的表达变化。该物种的雄性个体后足长有特化的、具有性二态性的腿节（femurs），这类后足会在雄性间的争斗中作为武器使用。雌性个体的整体体型通常大于雄性。本研究结果显示，在新型寄主上发育，会使性二态性状出现显著的表型可塑性变化。雄性后足腿节受新型寄主饮食的影响极为显著，甚至导致后足腿节的性二态性完全消失。此外，体型的性二态性反而增强：雄性成虫体型极小，而雌性成虫则能较好维持其固有体型。上述研究结果凸显了新型物种交互对性表型（sexual phenotypes）可能产生的复杂影响。