Community-wide genome sequencing reveals 30 years of Darwin’s finch evolution

A fundamental goal in evolutionary biology is to understand the genetic architecture of adaptive traits. Using whole-genome data of 3955 of Darwin’s finches on the Galápagos Island of Daphne Major, we identified six loci of large effect that explain 45% of the variation in the highly heritable beak size of Geospiza fortis, a key ecological trait. The major locus is a supergene comprising four genes. Abrupt changes in allele frequencies at the loci accompanied a strong change in beak size caused by natural selection during a drought. A gradual change in Geospiza scandens occurred across 30 years as a result of introgressive hybridization with G. fortis . This study shows how a few loci with large effect on a fitness-related trait contribute to the genetic potential for rapid adaptive radiation. The ability of an organism to respond to shifting selective pressures depends on the genetic architectures of the traits underlying adaptations. Examining four species of Darwin’s finches from the Galápagos Islands, Enbody et al . identified six loci with large effects on beak size that explain 59% of the total heritability in one of these species. The authors also connect the incidence of droughts, which result in changes in food availability, to shifts in the allele frequency of these loci, some of which are caused by hybridization between species. This study takes advantage of 30 years of study of a classic system to elucidate the role of genetic architecture and introgression in adaptation. —Corinne Simonti Natural selection and introgressive hybridization cause large changes in allele frequencies at beak-size loci.