Inversions maintain differences between migratory phenotypes of a songbird

Structural rearrangements have been shown to be important in local adaptation and speciation, but have been difficult to reliably identify and characterize in non-model species. Here we combine long reads, linked reads and optical mapping to characterize three divergent chromosome regions in the willow warbler Phylloscopus trochilus, of which two are associated with differences in migration and one with an environmental gradient. We show that there are inversions (0.4-13 Mb) in each of the regions and that the divergence times between inverted and non-inverted haplotypes are similar across the regions (similar to 1.2 Myrs), which is compatible with a scenario where inversions arose in either of two allopatric populations that subsequently hybridized. The improved genomes allow us to detect additional functional differences in the divergent regions, providing candidate genes for migration and adaptations to environmental gradients. Rearrangements in the genome are important for local adaptation and speciation but are often difficult to identify reliably. Here the authors show that rearrangements underlie large chromosome regions that separate differentially migratory willow warblers.

Automated summary

The authors used a combination of long reads, linked reads, and optical mapping to characterize three chromosomal regions in the willow warbler that are associated with migration differences and environmental gradients. They found inversions in each of the regions and similar divergence times between inverted and non-inverted haplotypes across the regions. The improved genomes allowed them to identify candidate genes for migration and adaptations to environmental gradients.