Microgeographic variation in morphology within populations of threespine stickleback

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Jiang, Cynthia

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Local adaptation, the evolution of traits that make native individuals in a population have higher fitness than foreign individuals, is studied intensively in the field of evolutionary biology. For local adaptation to occur, different habitats must select for different traits, and this divergent selection must be stronger than the homogenizing effect of selection. However, at small spatial scales, gene flow is believed to be the stronger evolutionary force, eroding any local adaptation. Yet, local adaptation can still occur at small spatial scales (‘microgeographic divergence’) if selection is strong, if individuals proactively choose their habitat, or if philopatric individuals adjust their phenotypes to their local environment. The goal of my research is to test for microgeographic divergence within populations of threespine stickleback. I analyzed morphological and trap data of threespine stickleback collected in 2013, to test for among-trap differences in morphological traits. I show that stickleback morphology differs among traps within lakes, and within streams. This microgeographic variation is stronger for some traits than for others and is only partly attributable to isolation by distance within lakes. Overall, the results provide support of microgeographic divergence, a concept that may be more widespread than evolutionary biologists have previously believed.


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