Data from: Are red bishops red enough? On the persistence of a generalized receiver bias in Euplectes

In the genus Euplectes (17 species of widowbirds and bishops), red carotenoid-based coloration has been found to function in male contest competition over territories and appears to exploit a generalized receiver bias by which redder (more longwave) hues are perceived as more aversive or intimidating. A major piece missing, however, is that among the 5 most extensively red species, forming the clade of “red bishops,” the agonistic function has remained unexplored or undetected. Moreover, does the receiver bias remain generalized (“open-ended”) after coevolution of the most exaggerated signal phenotypes? In this field experiment with southern red bishops E. orix, we increased the color hue 27nm, beyond its natural range, and compared the success in territorial competition of these supernormal red males to that of control-red and green (down-manipulated) males. The treatment, but no pre-manipulation colorimetrics or morphometrics, had a significant effect on territory establishment; 76% of super-red males, 45% of control-red males, and 17% of green males were recorded as territory holders at the end of the experiment. The receiver bias, that is, a generalized aversion of redder hues, thus appears to remain after the signal elaboration process, likely (but not necessarily) reinforced by adaptive receiver coevolution, through, for example, exploitation resistance or signal honesty.

在织雀属（Euplectes，包含17种寡妇鸟和主教雀）中，研究发现基于类胡萝卜素的红色羽色在雄鸟领地争夺竞争中发挥作用，且这类羽色似乎利用了广义接收者偏差（generalized receiver bias）——即偏红（长波光成分更多）的色调会被感知为更具威慑性或更令人反感。然而，现有研究仍存在一处关键空白：在构成“红色主教雀”演化支的5种红色最显著的物种中，其体色的争斗功能尚未被探索或发现。此外，在最夸张的信号表型发生共演化之后，这种接收者偏差是否仍保持广义性（即“开放式”）？本研究以南红主教雀（E. orix）为对象开展野外实验，将其体色色调提升27纳米，超出其自然变异范围，并将这些“超常红色”雄鸟与对照组红色雄鸟以及绿色（通过羽毛处理下调色度）雄鸟的领地竞争成功率进行对比。实验处理（而非处理前的色度测量或形态测量数据）对领地建立具有显著影响：实验结束时，76%的超常红色雄鸟、45%的对照组红色雄鸟以及17%的绿色雄鸟被记录为领地拥有者。由此可见，这种接收者偏差（即对偏红色调的广义厌恶）在信号强化过程后依然存在，且可能（但非必然）通过适应性接收者共演化（例如通过对抗信号利用或维持信号诚实性）得到增强。