Different Galápagos finch beaks persist within largely shared genomes
A single peer-reviewed study compared genomes and body measurements to examine contrasting beaks in Galápagos tree finches. Western populations with large beaks resembled small tree finches across much of their genomes but differed in a region called G03. The analysis, supported by measurements of museum specimens, suggests that distinctive forms can persist alongside gene exchange. Different genomic regions therefore carry different information about the evolutionary relationships of the same birds.
Science··Evening
Beak differences concentrate in one genomic region
A single peer-reviewed study compared large and small beak forms with genomes in tree finches on Ecuador’s Galápagos Islands. Western populations classified as large tree finches resembled small tree finches across much of their genomes. They nevertheless carried the large-beak form of a supergene region called G03. A supergene is a genetic region inherited as a linked unit. Different parts of the same bird’s genome thus form a mosaic carrying different relationships to neighbouring lineages.[1]
Genomes are examined alongside museum specimens
The genomic analysis covered 415 Darwin’s finches; tree finches accounted for 77 of those birds. Eight additional birds provided more distant comparisons, while body and beak measurements came from 348 museum specimens. The team compared whole-genome evolutionary trees with trees derived from particular regions. Removing the mosaic population from broader analyses revealed further regions of genetic divergence. Very small samples for some populations were identified as a limitation on regional comparisons.[1]
Signs of gene exchange accompany beak differences
Analyses of allele sharing and genetic diversity supported the interpretation that selection preserved distinctive forms alongside gene exchange. The separation between small- and large-beak G03 variants predates the recent diversification of tree finches. The data did not support a simple explanation in which a single founder bird supplied the large-beak variant. Gene exchange complicates evolutionary dating. The paper also describes how different genetic combinations can produce beak forms that look similar externally.[1]
