Department of Biological Sciences, 120 W. Samford Avenue, Auburn University, Auburn, AL, 36849, USA.
Department of Ecology, Evolution, and Organismal Biology, 2200 Osborne Drive, Iowa State University, Ames, IA, USA.
Biol Rev Camb Philos Soc. 2023 Dec;98(6):2320-2332. doi: 10.1111/brv.13008. Epub 2023 Aug 10.
Even as numerous studies have documented that the red and yellow coloration resulting from the deposition of carotenoids serves as an honest signal of condition, the evolution of condition dependency is contentious. The resource trade-off hypothesis proposes that condition-dependent honest signalling relies on a trade-off of resources between ornamental display and body maintenance. By this model, condition dependency can evolve through selection for a re-allocation of resources to promote ornament expression. By contrast, the index hypothesis proposes that selection focuses mate choice on carotenoid coloration that is inherently condition dependent because production of such coloration is inexorably tied to vital cellular processes. These hypotheses for the origins of condition dependency make strongly contrasting and testable predictions about ornamental traits. To assess these two models, we review the mechanisms of production of carotenoids, patterns of condition dependency involving different classes of carotenoids, and patterns of behavioural responses to carotenoid coloration. We review evidence that traits can be condition dependent without the influence of sexual selection and that novel traits can show condition-dependent expression as soon as they appear in a population, without the possibility of sexual selection. We conclude by highlighting new opportunities for studying condition-dependent signalling made possible by genetic manipulation and expression of ornamental traits in synthetic biological systems.
尽管许多研究已经证明，类胡萝卜素的沉积所产生的红色和黄色着色是健康状况的诚实信号，但健康状况的依赖性进化仍然存在争议。资源权衡假说提出，依赖于条件的诚实信号依赖于装饰性展示和身体维护之间的资源权衡。根据该模型，条件依赖性可以通过选择重新分配资源来促进装饰表达而进化。相比之下，指标假说则提出，选择侧重于对类胡萝卜素颜色的选择，而类胡萝卜素颜色本身就是条件依赖性的，因为这种颜色的产生与重要的细胞过程密不可分。这些关于条件依赖性起源的假说对装饰性特征做出了强烈对比和可测试的预测。为了评估这两个模型，我们回顾了类胡萝卜素的产生机制、涉及不同类胡萝卜素的条件依赖性模式以及对类胡萝卜素颜色的行为反应模式。我们回顾了一些证据，表明特征可以依赖于条件，而不受性选择的影响，并且新的特征可以在它们出现在种群中时立即表现出条件依赖性表达，而无需性选择的可能性。最后，我们强调了通过遗传操作和在合成生物系统中表达装饰性特征来研究条件依赖性信号传递的新机会。
