Centre for Ecology & Conservation, School of Biosciences, University of Exeter, Cornwall Campus, Penryn, UK.
School of Science, Western Sydney University, Hawkesbury Campus, Penrith, New South Wales, Australia.
J Evol Biol. 2023 Sep;36(9):1266-1281. doi: 10.1111/jeb.14198. Epub 2023 Aug 3.
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.
虽然许多关于雄性性特征进化的理论模型假设性选择会受到自然选择的抵制，但对这一假设的直接实证检验相对较少。众所周知，表皮碳氢化合物（CHCs）不仅在限制蒸发失水方面起着重要作用，而且在大多数陆地节肢动物的性信号传递中也起着重要作用。昆虫为了获得最佳的抗干燥能力而调整其 CHC 层，这通常被认为是以牺牲成功的性吸引力为代价的，这表明自然选择和性选择对此特征是相互对立的。在这项研究中，我们使用固相微萃取法对雄性黑蟋蟀（Teleogryllus commodus）的 CHCs 进行了采样，然后测量了它们的蒸发失水或交配成功率。然后，我们使用多元选择分析来量化针对雄性 CHCs 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 CHCs 施加了显著的线性和稳定选择，尽管针对的是非常不同的组合。自然选择在很大程度上有利于 CHC 总量的增加，尤其是那些具有更长链长的 CHC。相比之下，交配成功率在较低的 CHC 总量时达到峰值，并随着 CHC 丰度的增加而下降。然而，随着某些特定 CHC 成分的增加，交配成功率确实有所提高，而这些成分也会增加蒸发失水。重要的是，这导致了自然选择和性选择所青睐的雄性 CHC 组合强烈对立。我们的研究结果表明，在 T. commodus 中，自然选择和性选择之间的平衡很可能在雄性 CHC 的进化中发挥重要作用，并可能有助于解释为什么 CHC 在不同种群和物种之间如此多样化。
