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

The divergence-with-gene-flow model of speciation has a strong theoretical
basis with a growing number of plausible examples in nature, but remains
hotly debated. Darwin’s finches of the Galápagos Archipelago have played
an important role in our understanding of speciation processes. Recent
studies suggest that this group may also provide insights into speciation
via divergence with gene flow. On the island of Santa Cruz, recent studies
found evidence for adaptive divergence in Darwin’s small ground finch,
Geospiza fuliginosa, between ecologically contrasting arid and humid
zones. Despite the short geographical distance between these zones, strong
disruptive selection during low rainfall periods is expected to generate
and maintain adaptive divergence. Conversely, during high rainfall
periods, when disruptive selection is predicted to be weakened, population
divergence in adaptive traits is expected to break down. Because periods
of low and high rainfall irregularly alternate, the geographical pattern
of adaptive divergence can be assumed to break down and, importantly,
regenerate in situ. Here, we use microsatellite allele frequency data to
assess the genetic population structure of G. fuliginosa on Santa Cruz. We
sample 21 sites and four ecological zones across the island. We reject
hypotheses of population substructure linked to ecological and
geographical differences among sites in favour of a single panmictic
population. Panmixia implies high levels of gene flow within Santa Cruz,
which favours selection over genetic drift as a valid process generating
phenotypic divergence in G. fuliginosa on Santa Cruz. We discuss how our
findings may support classic adaptation, phenotypic plasticity, matching
habitat choice or any combination of these three processes.