Genomic signatures of isolation, hybridization, and selection during speciation of island finches

Sister species occurring sympatrically on islands are rare and offer unique opportunities to understand how speciation can proceed in the face of gene flow. The Sao Tome grosbeak is a massive-billed, giant finch endemic to the island of Sao Tome in the Gulf of Guinea, where it has diverged from its co-occurring sister species the Principe seedeater, an average-sized finch that also inhabits two neighbouring islands. Here, we show that the grosbeak carries a large number of unique alleles different from all three Principe seedeater populations, but also shares many alleles with the sympatric Sao Tome population of the seedeater, a genomic signature signifying divergence in isolation as well as subsequent introgressive hybridization. Furthermore, genomic segments that remain unique to the grosbeak are situated close to genes, including genes that determine bill morphology, suggesting the preservation of adaptive variation through natural selection during divergence with gene flow. This study reveals a complex speciation process whereby genetic drift, introgression, and selection during periods of isolation and secondary contact all have shaped the diverging genomes of these sympatric island endemic finches. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=60 SRC="FIGDIR/small/474904v1_ufig1.gif" ALT="Figure 1"> View larger version (41K): org.highwire.dtl.DTLVardef@5b18a5org.highwire.dtl.DTLVardef@af0c4forg.highwire.dtl.DTLVardef@512a60org.highwire.dtl.DTLVardef@b51c61_HPS_FORMAT_FIGEXP M_FIG C_FIG