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Willow Tit’s Three Major Genomic Lineages Closely Matched Its Main Song Types

Willow tit perched on a broken branch
Research · Genetics & genomics

Willow tit (Poecile montanus) song-type boundaries across Europe and Asia closely coincide with three deeply diverged genomic lineages, according to a preprint posted to bioRxiv on 24 April 2026. The study combined a chromosome-level reference genome, whole-genome resequencing and reconstructions of where suitable habitat may have existed during past climatic periods. It was posted as a preprint and had not yet undergone journal peer review, so the conclusions remain provisional.

The researchers analysed whole genomes from 88 willow tits representing all 14 recognised subspecies. Their reconstruction indicates an origin in Asia during the Late Pliocene to Early Pleistocene, followed by range expansions that produced three major genomic lineages in Asia, Central Europe and the Northern Palearctic.

Three song types matched the main genomic lineages

The three main song types are known as Lowland, Alpine and Sino-Japanese. Northern populations often combine Alpine and Lowland songs in a mixed “Siberian” repertoire. The researchers assigned song types to genetic samples using their locations and previously mapped song distributions. The boundaries between the three major genomic lineages closely matched these broad song divisions.

Maps and spectrograms of willow tit song types
Figure 1. Song distributions (A), subspecies ranges (B) and spectrograms of the three main song types (C). Stripes show the mixed Siberian repertoire. Range boundaries are approximate. Syarifa et al. (2026), bioRxiv, CC BY 4.0. Bird illustrations: Javier Lazaro. Song recordings: Ulrich Knief; Thijs Fijen (XC145196).

Gene flow was stronger between similar song types

Analyses of historical allele sharing—patterns in which populations share alleles in ways that can reveal past genetic exchange—also indicated that gene flow occurred preferentially among lineages with the same or similar song types, even after the researchers accounted for geographic distance. Gene flow means that successful reproduction moves genetic variants between populations. The authors interpret the pattern as consistent with song contributing to prezygotic isolation: behavioural differences may reduce mating between populations before fertilisation can occur.

Glacial isolation left bottleneck signals

Peripheral populations dominated by one song type showed genomic signatures of repeated population bottlenecks associated with past glacial isolation. A population bottleneck is a period when a population becomes much smaller, causing it to lose genetic variation. In contrast, large northern populations retained broader song repertoires and stronger signs that populations had remained genetically connected over long periods.

The authors suggest that culturally transmitted song may have helped maintain lineage boundaries over evolutionary time. Cultural transmission here means that song patterns can be passed socially between birds through learning. They also note that the extent to which willow tit song is actually learned remains incompletely understood: earlier experiments with hand-raised birds suggested that Alpine song might be largely innate, although those experiments were not standardised.

Sources and image credit

  1. Syarifa, A., Martens, J., Päckert, M., Kvist, L., Wu, L., Sun, Y.-H., Wolf, J. B. W., & Knief, U. (2026). Cultural transmission and genomic co-divergence in the willow tit across the Palearctic [Preprint]. bioRxiv.24 April 2026. Supplementary Table S3 lists the genomic sampling localities.

Image: Keith Gallie — willow tit at Pennington Flash, England, 11 November 2016. Representative photograph. Colour adjustment by MPF; cropped to 16:9. Source: Wikimedia Commons. · CC BY 2.0 · Source

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