Data from: Receiver discriminability drives the evolution of complex sexual signals by sexual selection

A hallmark of sexual selection by mate choice is the evolution of exaggerated traits, such as longer tails in birds and more acoustic components in the calls of birds and frogs. Trait elaboration can be opposed by costs such as increased metabolism and greater predation risk, but cognitive processes of the receiver can also put a brake on trait elaboration. For example, according to Weber's Law traits of a fixed absolute difference will be more difficult to discriminate as the absolute magnitude increases. Here we show that in the Emei music frog (Babina daunchina) increases in the fundamental frequency between successive notes in the male advertisement call, which increases the spectral complexity of the call, facilitates the female's ability to compare the number of notes between calls. These results suggest that female's discriminability provides the impetus to switch from enhancement of signaling magnitude (i.e. adding more notes into calls) to employing a new signal feature (i.e. increasing frequency among notes) to increase complexity. We suggest that increasing the spectral complexity of notes ameliorates some of the effects of Weber's Law, and highlights how perceptual and cognitive biases of choosers can have important influences on the evolution of courtship signals.配偶选择介导的性选择，其标志性特征之一是夸张性状的演化——例如鸟类更长的尾羽，以及鸟类与蛙类鸣叫声中更多的声学组分。性状的夸张强化往往会伴随代谢成本上升、被捕食风险增高等代价，但接收者的认知过程同样会对性状夸张强化形成制约。例如根据韦伯定律（Weber's Law），当绝对刺激量增大时，固定绝对差异的性状将更难被区分。 本研究以峨眉音乐蛙（Emei music frog，*Babina daunchina*）为研究对象，结果显示：雄性求偶鸣叫声的连续音节间基频提升，既增加了鸣叫声的频谱复杂度，同时也增强了雌性对不同鸣叫声间音节数量的比较判别能力。 上述结果表明，雌性的识别判别能力可作为演化驱动力，促使求偶信号的演化路径从提升信号规模（即于鸣叫声中增加更多音节）转向采用新的信号特征（即提升音节间的频率差）以增加信号复杂度。 我们认为，提升音节的频谱复杂度可在一定程度上缓解韦伯定律带来的影响，同时也凸显了择偶者的感知与认知偏差在求偶信号演化过程中所发挥的重要作用。