Book excerpt: "The threespine stickleback (Gasterosteus aculeatus) is one of the most extensively studied vertebrate species for gaining insights into adaptive radiation and contemporary evolution in the wild. This body of literature is made possible by the propensity of threespine sticklebacks to disperse across dramatic environmental gradients, into habitats where populations diverge in response to a wide variety of local selection pressures, including predators, prey, water chemistry, flow regimes, visibility, and parasites. For each of these selective pressures, multiple traits are involved in the adaptive responses of a population, and each trait may be under pressure from multiple agents of selection. As a consequence, assessment of inter-population differences in individual traits, or in traits as an assortment of uncorrelated parts, is insufficient to characterize divergence in either traits or the functions of those traits. Here I use multidimensional approaches to assessing morphological divergence between populations, with a special focus on high-resolution morphometric data gathered from micro computed tomography ([mu]CT) scans, and the morphological features associated with feeding. First, I show problems associated with the use of 2D shape data to characterize parallel evolution of morphology and function. I then demonstrate that divergence among populations is a process of moderate dimensionality in which groups of traits under similar selection pressures are correlated with one another to varying degrees. With repeated sampling of an introduced population, I show that following introduction to a novel habitat, different anatomical modules associated with feeding do not change at the same rate, and that already weak covariances among modules are disrupted. Finally, I document functional and morphological divergence in an atypical stickleback population, and demonstrate how a mechanism of divergence distinct from ecological or mutation-order speciation can be incorporated into the identification and conservation of biological diversity"--