Panmixia supports divergence with gene flow in Darwin’s small ground finch, Geospiza fuliginosa, on Santa Cruz, Galápagos Islands

Research on Darwin's small ground finch, Geospiza fuliginosa, on Santa Cruz Island reveals that despite ecological and geographical differences between arid and humid zones, the species exhibits panmixia—a single genetically homogeneous population. This finding challenges expectations of strong adaptive divergence due to disruptive selection during low rainfall periods. Using microsatellite allele frequency data from 21 sites across four ecological zones, scientists rejected hypotheses of population substructure linked to ecological or geographical differences. The study suggests that high gene flow within the island supports selection over genetic drift as a driver for phenotypic divergence. These insights imply that classic adaptation, phenotypic plasticity, habitat choice, or combinations thereof may explain observed trait variation without requiring distinct populations.

GALLIGAN, T. H., DONNELLAN, S. C., SULLOWAY, F. J., FITCH, A. J., BERTOZZI, T., & KLEINDORFER, S. (2012). Panmixia supports divergence with gene flow in Darwin’s small ground finch, Geospiza fuliginosa, on Santa Cruz, Galápagos Islands. Molecular Ecology, 21(9), 2106–2115. Portico. https://doi.org/10.1111/j.1365-294x.2012.05511.x