Although many theoretical models of male sexual trait evolution assume that sexual selection is countered by natural selection, direct empirical tests of this assumption are relatively uncommon. Cuticular hydrocarbons (CHCs) are known to play an important role not only in restricting evaporative water loss but also in sexual signalling in most terrestrial arthropods. Insects adjusting their CHC layer for optimal desiccation resistance is often thought to come at the expense of successful sexual attraction, suggesting that natural and sexual selection are in opposition for this trait. In this study, we sampled the CHCs of male black field crickets (Teleogryllus commodus) using solid-phase microextraction and then either measured their evaporative water loss or mating success. We then used multivariate selection analysis to quantify the strength and form of natural and sexual selection targeting male CHCs. Both natural and sexual selection imposed significant linear and stabilizing selection on male CHCs, although for very different combinations. Natural selection largely favoured an increase in the total abundance of CHCs, especially those with a longer chain length. In contrast, mating success peaked at a lower total abundance of CHCs and declined as CHC abundance increased. However, mating success did improve with an increase in a number of specific CHC components that also increased evaporative water loss. Importantly, this resulted in the combination of male CHCs favoured by natural selection and sexual selection being strongly opposing. Our findings suggest that the balance between natural and sexual selection is likely to play an important role in the evolution of male CHCs in T. commodus and may help explain why CHCs are so divergent across populations and species.

中文翻译：

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美观还是功能？自然选择和性选择对雄性黑田蟋蟀表皮碳氢化合物的相反影响。

尽管许多男性性特征进化的理论模型都假设性选择受到自然选择的抵制，但对这一假设的直接实证检验相对不常见。众所周知，角质层碳氢化合物（CHC）不仅在限制水分蒸发方面发挥着重要作用，而且在大多数陆地节肢动物的性信号传导中也发挥着重要作用。昆虫调整CHC层以获得最佳的抗干燥能力通常被认为是以牺牲成功的性吸引为代价的，这表明自然选择和性选择对于这一特性是相反的。在这项研究中，我们利用固相微萃取技术对雄性黑田蟋蟀 (Teleogryllus commodus) 的 CHC 进行了采样，然后测量了它们的蒸发失水量或交配成功率。然后，我们使用多变量选择分析来量化针对男性 CHC 的自然选择和性选择的强度和形式。自然选择和性选择都对雄性 CHC 施加了显着的线性和稳定选择，尽管组合非常不同。自然选择很大程度上有利于 CHC 总丰度的增加，尤其是那些链长较长的 CHC。相比之下，交配成功率在 CHC 总丰度较低时达到顶峰，并随着 CHC 丰度增加而下降。然而，随着一些特定 CHC 成分的增加，交配成功率确实有所提高，同时也增加了蒸发水分损失。重要的是，这导致了自然选择青睐的男性CHC与性选择强烈反对的结合。我们的研究结果表明，自然选择和性选择之间的平衡可能在 T. commodus 雄性 CHC 的进化中发挥重要作用，并且可能有助于解释为什么 CHC 在不同种群和物种之间如此不同。