Abstract
Birdsong is a culturally transmitted mating signal. Due to historical and geographical biases, song (learning) has been predominantly studied in the temperate zones, where female song is rare. Consequently, mechanisms and function of song learning have been almost exclusively studied in male birds and under the premise that inter- and intrasexual selection favoured larger repertoires and complex songs in males. However, female song is not rare outside the temperate zones and song in both sexes probably is the ancestral state in songbirds. Some song dimorphisms seen today might therefore be manifestations of secondary losses of female song. What selection pressures have favoured such losses and other sexual dimorphisms in song? Combined mapping of phylogenetic and ecological correlates of sex differences in song structure and function might provide important clues to the evolution of male and female song. This requires parameterization of the degree of sexual dimorphism. Simple comparison of male-female song might not provide enough resolution, because the same magnitude of difference (e.g. repertoire overlap) could result from different processes: the sexes could differ in how well they learn (‘copying fidelity’) or from whom they learn (‘model selection’). Different learning mechanisms might provide important pointers towards different selection pressures. Investigating sex-specific learning could therefore help to identify the social and ecological selection pressures contributing to sex differences in adult song. The study of female song learning in particular could be crucial to our understanding of i) song function in males and females and ii) the evolution of sex-specific song.
Highlights
The study of female song learning in particular could be crucial to our understanding of (i) song function in males and females and (ii) the evolution of sex-specific song
Some of the methods used for female preference testing, such as phonotaxis paradigms, are likely to work in males as well, because males have been shown to be attracted to and approach playback of female song in species with singing females (Langmore et al, 1996)
Learning and cultural transmission processes deeply impact the efficacy of the signal and both learned song and preferences are subjected to natural, social, inter- and intra-sexual selection processes
Summary
Behavioural Biology, Institute of Biology, Leiden University, Leiden, Netherlands. Mechanisms and function of song learning have been almost exclusively studied in male birds and under the premise that inter- and intra-sexual selection favored larger repertoires and complex songs in males. Combined mapping of phylogenetic and ecological correlates of sex differences in song structure and function might provide important clues to the evolution of male and female song. What selection pressures have favored such losses and other sexual dimorphisms in song? This requires parameterization of the degree of sexual dimorphism.
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