Supplementary Data S7. PGLS models - original output from Bare parts in the Galliformes: the evolution of a multifunctional structure

A morphological trait can have multiple functions shaped by varying selective forces. Bare parts in birds, such as wattles, casques and combs, are known to function in both signalling and thermoregulation. Studies have demonstrated such structures are targets of sexual selection via female choice in several species of Galliformes (junglefowl, turkeys and grouse), though other studies have shown some role in thermoregulation (guineafowl). Here, we tested fundamental hypotheses regarding the evolution and maintenance of bare parts in Galliformes. Using a phylogeny that included nearly 90% of species in the order, we evaluated the role of both sexual and natural selection in shaping the function of bare parts across different clades. We found a combination of both environmental and putative sexually selected traits strongly predicted the variation of bare parts for both males and females across Galliformes. When the analysis is restricted to the largest family, Phasianidae (pheasants, junglefowl and allies), sexually selected traits were the primary predictors of bare parts. Our results suggest that bare parts are important for both thermoregulation and sexual signalling across Galliformes but are primarily under strong sexual selection within the Phasianidae.

形态性状可受不同选择压力塑造，进而兼具多种功能。鸟类的裸露躯体结构（如肉垂、头盔与肉冠）已知兼具性信号传递与体温调节功能。已有研究证实，在数种鸡形目（Galliformes）物种（如原鸡、火鸡与松鸡）中，这类结构是雌性选择介导的性选择作用靶点；不过另有研究表明，其在体温调节中也发挥一定功能（如珠鸡）。本研究针对鸡形目鸟类裸露结构的演化与维持机制检验了核心假说。本研究采用覆盖该目近90%物种的系统发育树，评估了性选择与自然选择在不同演化支中对裸露结构功能的塑造作用。研究发现，环境因素与推定的性选择性状的联合效应，可显著预测鸡形目雌雄个体裸露结构的变异程度。当分析范围限定于该目最大的科——雉科（Phasianidae，雉类、原鸡及其近缘类群）时，性选择性状成为裸露结构变异的主要预测因子。本研究结果表明，鸡形目鸟类的裸露结构兼具体温调节与性信号传递的重要功能，但在雉科类群中，其演化主要受强烈的性选择驱动。