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UBC Theses and Dissertations

Song in a hybrid zone between Townsend’s (Setophaga townsendi) and black-throated green (S. virens) warblers Kenyon, Haley Linnell


Song is one of the most widely recognized premating barriers to reproduction between avian species. In oscines both genetic and cultural inheritance contribute to an individual’s song phenotype, contributing to difficulty in predicting the role that song may play in reproductive isolation; interspecific song learning could promote interbreeding. Here I seek to better understand this phenomenon by studying song in a narrow hybrid zone between black-throated green (Setophaga virens) and Townsend’s warblers (S. townsendi). I use multivariate analyses to compare songs in the hybrid zone to those found in allopatry, predicting that if song is a strong barrier to interbreeding, then there should be a relationship between song and genotype in the hybrid zone. I employ a genotyping-by-sequencing (GBS) method to identify thousands of markers and develop two hybrid indices. Playback experiments were carried out in the field to test responses to parental songs, and a cline analysis was conducted in order to compare transitions in genotype and song across the hybrid zone. I show that only parental song types are found in the hybrid zone, and furthermore, that there is little if any association between song and genotype in sympatric individuals; this suggests that song is not an important reproductive barrier. Allopatric individuals responded only to local songs, indicating that individuals may exhibit a learned response to songs that they are commonly exposed to. Out of thousands of genomic markers, I identified few that were diagnostic, suggesting that much of the genome may introgress freely between these species. I observed discordance between the song and genotype clines; the song cline was much narrower indicating that song is under stronger selection. Taken together, these findings combine to suggest that song is not a reproductive barrier in this hybrid zone, but is instead a cultural trait that is maintained by frequency-dependent selection. Thus, it may be more beneficial for males to sing a locally common song than to broadcast accurate species-membership information.

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