Different Look, Same DNA
In a recent study, nestling swamp sparrows of coastal and inland subspecies were raised in captivity. When they reached adulthood, their plumage and bill size differed, just as they do in wild populations; the coastal birds became larger-billed and had darker feathers.
Therefore, the differences between the subspecies are due to genetic differences. However, various comparisons of the DNA have not revealed substantial differences between them, their DNA cannot be told apart.
This is likely because they have only recently (perhaps 10,000 years) become separated from each other. Their different environments, coastal salt marshes versus inland bogs, exhibit strong selective pressures but the lack of time of their separation has not been enough for their DNA divergance to be detectable.
The birds involved in this experiment can be viewed at the National Zoo's Bird House in Washington, D.C.
This article summarizes the information in this scientific paper:
Ballentine, B., and Greenberg, R. 2010. Common Garden Experiment Reveals Genetic Control of Phenotypic Divergence between Swamp Sparrow Subspecies That Lack Divergence in Neutral Genotypes. PLoS ONE 5(4): e10229. doi:10.1371/journal.pone.0010229
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