Andersson Staffan, Pryke Sarah R, Ornborg Jonas, Lawes Michael J, Andersson Malte
Department of Zoology, Göteborg University, Box 463, SE-405 30 Göteborg, Sweden.
Am Nat. 2002 Nov;160(5):683-91. doi: 10.1086/342817.
Sexual displays often involve several different ornamental traits. Yet most indicator models of sexual selection based on a single receiver (usually a choosy female) find that multiple handicap signals should be unstable. Here we study reasons for this contradiction, analyzing signal function, signal content, and trade-offs between signals in the polygynous red-collared widowbird Euplectes ardens. Males have both a long, graduated tail and a red carotenoid collar badge. Territory-holding "residents" have slightly shorter tails than the nonbreeding "floaters," but their carotenoid collars are 40% larger, and they have (on the basis of reflectance spectrometry and objective colorimetry) a 23-nm more long-wave ("redder") hue than floaters. This corroborates experimental evidence that the red collar is selected by male contest competition, whereas female choice is based almost exclusively on male tail length. Tail length is negatively correlated with the carotenoid signal, which together with body size and condition explains 55% of the variation in tail length. The trade-off in tail length and carotenoid investment is steeper among residents, suggesting an interaction with costs of territory defense. We propose that the "multiple receiver hypothesis" can explain the coexistence of multiple handicap signals. Furthermore, the trade-off between signal expressions might contribute to the inverse relation between nuptial tail elongation and coloration in the genus Euplectes (bishops and widowbirds).
求偶展示通常涉及几种不同的装饰性特征。然而，大多数基于单一接收者（通常是挑剔的雌性）的性选择指标模型发现，多个不利条件信号应该是不稳定的。在这里，我们研究这种矛盾产生的原因，分析信号功能、信号内容以及一夫多妻制的红领寡妇鸟（Euplectes ardens）中信号之间的权衡。雄性既有一条长的渐变尾羽，又有一个红色类胡萝卜素颈圈标志。拥有领地的“居民”的尾羽比非繁殖期的“游荡者”略短，但其类胡萝卜素颈圈要大40%，并且根据反射光谱法和客观比色法，它们的色调比游荡者的长23纳米（“更红”）。这证实了实验证据，即红色颈圈是通过雄性间的竞争选择的，而雌性选择几乎完全基于雄性尾羽的长度。尾羽长度与类胡萝卜素信号呈负相关，这与体型和身体状况共同解释了尾羽长度变化的55%。居民中尾羽长度和类胡萝卜素投入之间的权衡更为明显，这表明与领地防御成本存在相互作用。我们提出“多个接收者假说”可以解释多个不利条件信号的共存。此外，信号表达之间的权衡可能导致了主教鸟属和寡妇鸟属（Euplectes）中婚羽尾羽延长与色彩之间的反比关系。
