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Quantifying adaptive evolution: three‐dimensional phenotypes provide new insight into mechanisms of rapid evolutionary change in threespine stickleback (918.28)

How do evolutionary transitions occur following environmental change? Threespine stickleback (Gasterosteus aculeatus) are among the most well‐studied natural examples of rapid evolutionary change. They provide an ideal model with which to examine the means by which many parallel examples of adaptive phenotypic modification can occur over very short periods of time. Here we discuss the results of two studies employing a three‐dimensional (3D) approach to phenotypic quantification, combining the techniques of micro‐computed tomography and geometric morphometrics with the tools of molecular ecology to gain new insight into the mechanisms driving adaptive change. First, we tested the hypothesis that two freshwater populations originating from the same putative ancestral population have diverged to more closely resemble each other than they do their recent common ancestor. We demonstrate that sticklebacks establishing new populations in Alaskan freshwater lakes follow similar phenotypic trajectories. Second, we used a quantitative trait locus analysis of a marine‐freshwater cross from British Columbia to test the hypothesis that a small number of loci of large effect are responsible for marine‐freshwater phenotypic divergence. We recover both previously identified QTL as well as a new, previously unreported loci with the potential for wide‐ranging effects on skeletal development. We discuss the framework of an integrative research program aimed at elucidating the means by which key characteristics of the phenotype may allow organisms to adapt rapidly to changing environments.