Congrats to Erik for his recent publication in Nature Communications about an inversion supergene he disocvered in redpoll finches! Redpolls have puzzled birders and taxonomists for centuries because it is difficult to determine what "species" you're looking at. In 2015 Nick Mason and Scott published a paper in Molecular Ecology showing that redpolls lack population genetic differetiation across the entire Holarctic but that gene expression variation correlated strongly with redpoll plumage and bill morphology. Erik's results explain why! The supergene haplotype possessed by an individual strongly correlates with their plumage and bills while the rest of the genome has been homogenized by gene flow.