1. Sexual selection leads to the expression and maintenance of colourful signals. The metabolic pathways to produce such signals often involve toxic byproducts that can reduce survival. However, rather than discarding these otherwise harmful byproducts, animals may use them by integrating them into sexually selected traits.
2. We tested this using the damselfly Hetaerina americana, where males bear a red wing spot (RWS) that has evolved by intrasexual competition.
3. By using confocal microscopy and several biochemical techniques, we determined that the RWS are generated by ommochrome pigments derived from tryptophan metabolism.
4. Second, we injected a group of males with the toxic precursor of these ommochromes, 3-hydroxy-kynurenine (3-Hk), confirming the toxicity of this compound in adult males.
5. Finally, we showed that adult males injected with a median lethal concentration of 3-Hk had more ommochromes in their RWS than controls but similar survival, suggesting that the deposition of ommochrome pigment in the wing counteracts the 3-HK toxicity.
6. Thus, we report that sexually selected pigmented signals may involve the co-option of excreted compounds that could otherwise have lethal effects, a hypothesis we call ‘detoxifying ability signalling’. Our results provide new insights about the evolution of sexual signals, elucidating a mechanism for the evolution of honest indicators of quality that could have arisen due to natural selection.

中文翻译：

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杀不死你的会让你更强大：排毒能力是性选择信号中诚实的机制

1. 性选择导致多彩信号的表达和维持。产生此类信号的代谢途径通常涉及可降低存活率的有毒副产物。然而，与其丢弃这些有害的副产品，动物可能会通过将它们整合到性选择特征中来使用它们。
2. 我们使用豆娘Hetaerina americana对此进行了测试，其中雄性带有通过性内竞争进化而来的红翼斑 (RWS)。
3. 通过使用共聚焦显微镜和几种生化技术，我们确定 RWS 是由色氨酸代谢衍生的全色色素产生的。
4. 其次，我们给一组雄性注射了这些单色素的有毒前体，3-羟基犬尿氨酸 (3-Hk)，证实了这种化合物对成年雄性的毒性。
5. 最后，我们发现注射了中位数致死浓度 3-Hk 的成年雄性在其 RWS 中比对照具有更多的 ommochromes，但存活率相似，这表明 ommochrome 色素在翅膀中的沉积抵消了 3-HK 的毒性。
6. 因此，我们报告说，性选择色素信号可能涉及排泄的化合物的共同选择，否则可能会产生致命影响，我们称之为“解毒能力信号”的假设。我们的结果提供了关于性信号进化的新见解，阐明了可能由于自然选择而产生的诚实质量指标的进化机制。