Directional sexual selection drives the evolution of traits that are most closely linked to reproductive success, giving rise to trait exaggeration and sexual dimorphism. Exaggerated structures are often costly and, therefore, thought to be expressed in a condition-dependent manner. Sexual selection theory thus predicts a direct link between directional sexual selection, sexual dimorphism, and sex-specific condition dependence. However, only a handful of studies investigate the relationship between sexual dimorphism and condition dependence. Using 21 genetic lines of Drosophila prolongata, we here compared the degree of sexual dimorphism and sex-specific condition dependence, measured as allometric slopes, in sexually selected and non-sexual traits. Our data revealed male-biased sexual dimorphism in all traits examined, most prominently in the sexually selected forelegs. However, there was no relationship between the degree of sex-specific condition dependence and sexual dimorphism across traits and genetic lines. Our results contradict theoretical predictions and highlight the importance of understanding the role of exaggerated traits in the context of both sexual and natural selection.

定向性选择推动了与繁殖成功最密切相关的性状的进化，从而导致性状夸大和性别二态性。夸张的结构通常代价高昂，因此被认为是以条件依赖的方式表达的。因此，性选择理论预测定向性选择、性二态性和性别特定条件依赖之间存在直接联系。然而，只有少数研究调查了性别二态性和条件依赖性之间的关系。使用 21 个Drosophila prolongata遗传系, 我们在这里比较了性别选择和非性特征的性二态性和性别特异性条件依赖性的程度，以异速生长斜率衡量。我们的数据显示，在所检查的所有性状中都存在男性偏见的性二态性，最突出的是在性选择的前肢中。然而，性别特异性条件依赖程度与跨性状和遗传系的性别二态性之间没有关系。我们的结果与理论预测相矛盾，并强调了理解夸大特征在性和自然选择背景下的作用的重要性。