The impact of culturally transmitted birdsong on genetic divergence in willow tits

• Applicant: Dr. Ulrich Knief
• Subject Area: Evolution, Anthropology
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 521246704

Cultural traits are “learned by any process of nongenetic transmission, whether by imprinting, conditioning, observation, imitation, or as a result of direct teaching”, which firmly places culture within biology more broadly. Indeed, culture has been observed across diverse taxonomic groups including insects, fish, reptiles, birds and mammals. Culture may have its greatest impact on genetic evolution by generating population genetic structure and initiating speciation. Birdsong is an excellent system for the study of cultural speciation because it is learned in most oscine passerines and it is the target of culturally-transmitted mating preferences. Therefore, birdsong can be subject to sexual selection, potentially leading to the build-up of prezygotic barriers to gene flow between populations. However, the extent to which culture affects the evolution of new species is currently debated and will be the main topic of my research. Specifically, what happens to hybridizing species if both mating trait (song) and preference are culturally transmitted? In this case, the question is whether divergence between species is promoted or whether they collapse back into one, because learning from unrelated tutors could cause a disassociation between genetic ancestry and learned song. Alpine and willow tits are an ideal model system to study the impact of culturally transmitted birdsong on genetic divergence because they (1) have different song types that are monomorphic across vast geographic areas, (2) have a simple song structure, which is readily classifiable, (3) repeatedly form narrow hybrid zones where different song types meet and subspecies interbreed and (4) do not exhibit obvious plumage or morphological differences between populations with alternative song types which makes song the explicit (prezygotic) reproductive barrier - a condition absent from other studies focusing on the effects of song on reproductive isolation. The geographic distribution of song types suggests that natural or sexual selection is stabilizing the hybrid zones. This allows testing whether population genetic structure is tightly coupled with male song and the female’s preference for it, and involves genomic and behavioral assays in the wild. Specifically, I will address the following questions: For how long have alpine and willow tits been separated and do we observe localized “genomic barrier loci”? Are the song types linked to these barrier loci in the hybrid zones between the two species? What is the role of assortative mating based on song in the maintenance of species boundaries? Overall, my research will assess the effect of culturally transmitted birdsong on genetic divergence between species, stimulate ongoing debates on the relative importance of prezygotic versus postzygotic reproductive isolation, reinforcement and sympatric speciation by using an interdisciplinary experimental approach and may provide direct evidence for speciation through cultural traits.

• DFG Programme: Research Grants