Is there an alternative route towards adaptation besides natural selection? An experimental test

This project (funded by an Explora-grant and an Excellence-grant from the Spanish Ministry for Science) with Zebra finches shares the theoretical foundation with the project with grasshoppers, and aimed to provide a proof-of-principle that Matching Habitat Choice can spatially subdivide and diverge a group of individual with respect to their ecological traits. Individuals exert Matching Habitat Choice if they somehow evaluate their ecological performance in one or more local habitats, and based on this information choose to stay in or leave a given habitat. If individuals have different phenotypes, then this may affect their local performance, and therefore the choice of habitat may vary between individuals as well. For example, large-billed birds may prefer habitat with large seeds whereas small-billed birds prefer habitat with small seeds. Hence movement, dispersal and gene flow are driven by individual differences. This can lead to local adaptation and spatial genetic structuring. To test this prediction empirically we replaced seed sizes with two kinds of feeders that give access  or not to food (divergent habitats), depending on the type of electronic transponder (RFID-chip or PIT-tag) that the finches carry. And we replaced bill sizes with the type of transponder (divergent ecological trait). By moving feeders across space, we evaluated if individuals change their use of the habitat, their choice of breeding location, and as an indirect side-effect their choice of partner, even leading to (partial) reproductive isolation and experimental speciation. We have done three repeats of this experiment and have genotyped all offspring to determine paternity, and the results are very exciting!