Male receiver bias for red agonistic signaling in a yellow-signaling widowbird: a field experiment

Receiver bias models of signal evolution are typically regarded as alternatives or complements to ornament evolution due to coevolving mate choice, whereas sexually or socially selected agonistic signals are rarely studied with respect to receiver psychology. Against the background of convergent evolution of red agonistic signals from yellow ancestors in the genus Euplectes (widowbirds and bishops), we experimentally test the function of a yellow signal in the montane marsh widowbird (E. psammocromius), as well as a hypothesized receiver bias for redder (longer wavelength) hues. In a field experiment in southern Tanzania, males that had their yellow wing patches blackened lost their territories or lost territorial contests more often than controls or reddened males, which together with a longer wavelength hue in territory holders, indicates an agonistic signal function. Males painted a novel red hue, matching that of red-signalling congeners, retained their territories and won contests ...

信号进化的接收者偏倚模型（Receiver bias models of signal evolution）通常被视为装饰特征进化（ornament evolution）的替代或补充理论，其立论基于协同演化的配偶选择机制；然而针对性选择或社会选择介导的争斗信号（sexually or socially selected agonistic signals），学界鲜有从接收者心理（receiver psychology）视角展开的研究。
鉴于寡妇鸟属（Euplectes，俗称寡妇鸟与主教雀）中红色争斗信号由黄色祖先趋同进化（convergent evolution）而来的研究背景，本研究以山地沼泽寡妇鸟（E. psammocromius）为实验对象，一方面验证其黄色信号的功能，另一方面检验关于接收者对更偏红（波长更长）色调存在偏倚的假说。
在坦桑尼亚南部开展的野外实验（field experiment）中，翼部黄色斑块被涂黑的雄性个体，相比对照组或被染成红色的个体，更易丢失领地或在领地争斗（territorial contests）中失利；结合领地持有者翼斑色调波长更长的观测结果，可证实该黄色信号具备争斗信号的功能。
被染成与具红色信号的同属物种（congeners）色调一致的新型红色调的雄性个体，则成功保留领地并赢得了争斗……