Multivariate evolution in replicated adaptive radiations: pattern, process and the role of the environment.

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The studies of ecology and evolution are closely related. Ecologists seek to understand the environmental factors that explain the distribution and abundance of species, while evolutionary biologists investigate the process of natural selection and the evolution that results, by examination of adaptation in phenotypes and genotypes. It is curious in these times of environmental change that one of the biggest gaps in our understanding of the natural world falls exactly at the intersection between ecology and evolution: we know less than we should about how the environment shapes the evolution of biodiversity. Although it is generally understood that the environment is the cause of adaptation, the links between them have seldom been explicitly explored. Many ecological studies do not consider how the environmental variation that they measure affects evolution, while many studies of evolution measure selection or adaptation without considering their environmental causes, concentrating instead on the consequences for evolution of what is genetically possible.Explicit study of the involvement of the environment in evolution has the potential to fuel a paradigm shift in our comprehension of fundamental evolutionary patterns. For example: (i) Divergence. Evolution has resulted in abundant diversity in the natural world, but the extent of this divergence within related groups of organisms is often circumscribed. Are these limits, on the kind of organisms that evolve, a consequence of what is genetically possible, or do they result from similarities in the environments to which the organisms are exposed? (ii) Convergence. Within the greater divergence, organisms have often apparently converged on similar evolutionary solutions, suggesting that evolutionary outcomes are to some extent repeatable. Is the repeated evolution of similar organisms in different places the result of genetic biases or environmental determinants? If the latter, do similar organisms always evolve in similar environments, or can different environments favour the same outcome of organismal form? Vice versa, do similar environmental combinations always result in essentially the same organism, or are there different evolutionary solutions to similar environmental problems? (iii) Novelty. Although similar organisms in different places often converge on repeated evolutionary solutions, evolution also occasionally comes up with solutions that are different from the general pattern, by dint of developing, or having lost, some distinguishing feature or combination of features. Is such evolutionary novelty the result of particularly unusual environments? Most previous studies of how the environment affects evolution have measured only a single, or small number of aspects of both the organism and the environment, but thorough answers to the questions we pose require a more comprehensive understanding of multiple different aspects of organism and environment, and of how they interact and affect other. Our approach requires the use of recently developed multivariate statistical methods that allow the simultaneous analysis of many organismal traits and many environmental variables.Adaptive radiation is the differentiation of an ancestral species into divergent new populations or species. The abundance of variation in both environment and biodiversity make adaptive radiations the perfect natural laboratories to address our questions. We will use data from replicated adaptive radiations of three-spined stickleback fish in Scotland, Iceland, western Canada and Alaska in order to answer our questions and achieve a comprehensive understanding of how the environment affects evolution. Three-spined stickleback are originally marine fish that have invaded freshwater throughout the northern hemisphere since the last ice age. Freshwater stickleback can occupy contrasting environments and exhibit great phenotypic variation, providing a perfect system for our study.