title: Receiver discriminability drives the evolution of complex sexual signals by sexual selection.
abstract: 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.
authors.affiliation: Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu, Sichuan, 610041, China. cuijg@cib.ac.cn.
authors.forename: Jianguo
authors.initials: J
authors.lastname: Cui
authors.affiliation: Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu, Sichuan, 610041, China.
authors.forename: Xiaowei
authors.initials: X
authors.lastname: Song
authors.affiliation: Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu, Sichuan, 610041, China.
authors.forename: Bicheng
authors.initials: B
authors.lastname: Zhu
authors.affiliation: Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu, Sichuan, 610041, China.
authors.forename: Guangzhan
authors.initials: G
authors.lastname: Fang
authors.affiliation: Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu, Sichuan, 610041, China. tangyz@cib.ac.cn.
authors.forename: Yezhong
authors.initials: Y
authors.lastname: Tang
authors.affiliation: Department of Integrative Biology, University of Texas, 1 University Station C0930, Austin, Texas, 78712.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Ryan
mesh_terms: D000818:Animals; D005075:Biological Evolution; D005260:Female; D008297:Male; D011898:Ranidae / Q000502:physiology*; D012726:Sexual Behavior, Animal; D014828:Vocalization, Animal
keywords: Acoustic communication; Weber's Law; sexual selection; signal evolution