genomic and morphological analysis of the red-backed fairy-wren hybrid zone
On a coarse geographic scale, the observation that the genetic barrier and the zone of plumage color overlap between Red-backed Fairy-wren subspecies do not occur in the same area suggests that there may have been asymmetrical introgression of alleles for red plumage across the genetic barrier once the subspecies came into secondary contact. To test this hypothesis , I used genomic and plumage color data in a geographic cline analysis of the hybrid zone. I used the reduced representation genomic technique genotyping-by-sequencing to create a large, genome-wide single nucleotide polymorphism (SNP) database. I compared variation in allele frequencies at these SNP loci to variation in plumage color across a 3,052 km transect through the hybrid zone encompassing nearly the entire species range.
Clines for many unlinked SNP loci (grey and black clines on figure) were centered at the Carpentarian Barrier, confirming that it is the location of secondary contact between the subspecies. However the center and width of these genetic clines varied substantially, with some introgressing freely by neutral diffusion and others subject to weak selection. The cline for plumage color (red cline on figure) was displaced 390 km east of the genetic clines, indicating that alleles for red plumage have introgressed asymmetrically across the hybrid zone, likely driven by sexual selection.
Clines for many unlinked SNP loci (grey and black clines on figure) were centered at the Carpentarian Barrier, confirming that it is the location of secondary contact between the subspecies. However the center and width of these genetic clines varied substantially, with some introgressing freely by neutral diffusion and others subject to weak selection. The cline for plumage color (red cline on figure) was displaced 390 km east of the genetic clines, indicating that alleles for red plumage have introgressed asymmetrically across the hybrid zone, likely driven by sexual selection.
