Divergence and gene flow among Darwin's finches: A genome-wide view of adaptive radiation driven by interspecies allele sharing

Abstract

A recent analysis of the genomes of Darwin's finches revealed extensive interspecies allele sharing throughout the history of the radiation and identified a key locus responsible for morphological evolution in this group. The radiation of Darwin's finches on the Galápagos archipelago has long been regarded as an iconic study system for field ecology and evolutionary biology. Coupled with an extensive history of field work, these latest findings affirm the increasing acceptance of introgressive hybridization, or gene flow between species, as a significant contributor to adaptive evolution. Here, we review and discuss these findings in relation to both classical work on Darwin's finches and contemporary work showing similar evolutionary signatures in other biological systems. The continued unification of genomic data with field biology promises to further elucidate the molecular basis of adaptation in Darwin's finches and well beyond.

Keywords: adaptation; adaptive radiation; genomics; hybridization; introgression.

Figure 1. Representatives of the Darwin's finch radiation

Illustrations from Birds Part 3 No. 4 (1839) and Birds Part 3 No. 5 (1841) of The zoology of the voyage of H.M.S. Beagle by John Gould, edited by Charles Darwin. Reproduced with permission from John van Wyhe ed. 2002-. The Complete Work of Charles Darwin Online. (http://darwin-online.org.uk/)

Figure 2. Maximum-likelihood phylogenies of Darwin's finches

Dashed arrows indicate gene flow between species. Highlighted bars denote key discordances between the trees. Branches ending with triangles indicate multiple genomes. Letters after species names indicate island sampled: S: Santiago, E: Española, L: San Cristóbal, Z: Santa Cruz, F: Fernandina, C: Cocos, P: Pinta, Fl: Floreana, I: Isabela, M: Daphne, D: Darwin, W: Wolf, G: Genovesa.

Figure 3. Haplotype tree of beak shape locus ALX1

Neighbor-joining tree based on ALX1 reveals a deep split between blunt and pointed beak haplotypes. Representative finch heads reflect species grouping by beak morphology as opposed to historical branching order. Branches ending with triangles indicate multiple ALX1 haplotype sequences.

Figure 4. Summary of recent studies of adaptive introgression in animals

Examples highlight the exchange of distinct adaptive phenotypic traits between species.