The 1964 Alaskan earthquake was landscape-altering in creating/uplifting numerous islands in the Gulf of Alaska, providing an ideal system to study adaptive evolution of diversification in affected species – the threespine stickleback (Gasterosteus aculeatus) being a widely studied example. In a recent manuscript, Lescak et al. (2015) sample >1000 sticklebacks across three such islands (Middleton, Montague, and Danger – 21 populations in all), and analyze the recent evolutionary history of these populations using >130,000 SNP’s and morphometric measurements.
As observed in several other (and older) populations of sticklebacks, oceanic versus freshwater individuals showed significant phenotypic divergence (various length measurements, number of lateral plates). Similarly, genotypic variation also partitioned between oceanic and freshwater fish – taken together, population structure analyses revealed the most likely number of subpopulations to be 2, with a Principal Components Analysis (PCA) presenting a continuum from oceanic to freshwater genotypes along PC1. Population assignment also revealed that the pre-existing (prior to 1964) freshwater populations on Middleton island to be uniquely clustering, and thus not indicative of having founded other populations on the island. Finer scale analyses of population structure point to several independent founding events on all three islands, with possible continuing migration and introgression from oceanic environments – furthering support for the “transporter” hypothesis in standing genetic variation being maintained by continued introgression between freshwater and oceanic stickleback.
These data argue that rapid parallel evolution over decades in stickleback may occur frequently because it is underlain by a pliant genomic architecture that is itself the product of millions of years of evolution…If the findings from stickleback are generalizable to other systems, then rapid evolution in the wild may be more common than previously documented.
Lescak, Emily A., et al. “Evolution of stickleback in 50 years on earthquake-uplifted islands.” Proceedings of the National Academy of Sciences (2015): 201512020. DOI: | http://dx.doi.org/10.1073/pnas.1512020112