Data from: Carotenoid coloration is related to fat digestion efficiency in a wild bird

Some of the most spectacular visual signals found in the animal kingdom are based on dietarily derived carotenoid pigments (which cannot be produced de novo), with a general assumption that carotenoids are limited resources for wild organisms, causing trade-offs in allocation of carotenoids to different physiological functions and ornamentation. This resource trade-off view has been recently questioned, since the efficiency of carotenoid processing may relax the trade-off between allocation toward condition or ornamentation. This hypothesis has so far received little exploratory support, since studies of digestive efficiency of wild animals are limited due to methodological difficulties. Recently, a method for quantifying the percentage of fat in fecal samples to measure digestive efficiency has been developed in birds. Here, we use this method to test if the intensity of the carotenoid-based coloration predicts digestive efficiency in a wild bird, the house finch (Haemorhous mexicanus). The redness of carotenoid feather coloration (hue) positively predicted digestion efficiency, with redder birds being more efficient at absorbing fats from seeds. We show for the first time in a wild species that digestive efficiency predicts ornamental coloration. Though not conclusive due to the correlative nature of our study, these results strongly suggest that fat extraction might be a crucial but overlooked process behind many ornamental traits.

动物界中最为引人注目的视觉信号之一，多源自膳食来源的类胡萝卜素（carotenoid）色素——这类色素无法通过从头合成（de novo）获得。学界普遍认为，类胡萝卜素对于野生生物而言是限制性资源，这使得生物在将类胡萝卜素分配至不同生理功能与装饰性结构时产生权衡。这一资源权衡观点近来受到了质疑，因为类胡萝卜素处理效率或许会缓解向机体状态或装饰结构分配的权衡。截至目前，这一假说几乎未获得探索性支持，原因在于野生生物消化效率的研究受限于方法学难度。近期，鸟类研究领域已开发出一种通过量化粪便样本脂肪百分比以衡量消化效率的方法。本研究借助该方法，旨在检验野生鸟类家朱雀（Haemorhous mexicanus）体内基于类胡萝卜素的体色强度是否能够预测其消化效率。研究结果显示，类胡萝卜素羽毛着色的红度（色调）与消化效率呈正相关，体色更红的个体从种子中吸收脂肪的效率更高。我们首次在野生物种中证实，消化效率可预测装饰性体色特征。尽管本研究为相关性研究，尚未得出确定性结论，但上述结果强烈表明，脂肪提取过程或许是诸多装饰性性状背后关键却长期被忽视的机制。