Admixture mapping among three hybridizing sapsucker (Sphyrapicus) species shows importance of the Z chromosome in phenotypic differentiation and speciation

Plumage pigmentation, a key aspect of sexual and natural selection in birds, is of great interest when investigating genomic mechanisms behind color differences between species. Three species of North American woodpeckers offer a unique opportunity to study this phenomenon: the red-breasted (Sphyrapicus ruber), red-naped (S. nuchalis), and yellow-bellied sapsuckers (S. varius). Their breeding ranges are mostly separated yet adjacent, with hybrid zones emerging at their meeting points.

The species with the most similar plumage coloring (S. varius and S. nuchalis) is not the most closely related pair genetically (S. nuchalis and S. ruber). This discrepancy allows researchers to identify which parts of the genome contribute to plumage color variation. By analyzing whole genome sequences from each species and hybrids from each species pair using admixture mapping, scientists discovered strong links between plumage coloration and wide segments of the Z-chromosome.

These findings reveal how modifications in a single sex chromosome can result in minor pigment changes (S. varius vs. S. nuchalis) or significant shifts ranging from dimorphism to monomorphism, and from predominantly black and white to primarily red coloring (S. varius and S. nuchalis vs. S. ruber).