The Study of Local Adaptation: A Thriving Field of Research

When individuals have higher fitness in their local environment than individuals from elsewhere, this is termed local adaptation (Williams 1966). This occurs when natural selection acts on traits differently depending on environmental conditions, which can vary in both space and time. Classically, tests for local adaptation involve reciprocal-transplant experiments that involve moving individuals among sites and measuring their performance relative to a home/local versus away/foreign scenario, such that a measure of fitness can be obtained. This approach has a long tradition. Following in the footsteps of Turesson (1922), who performed common-garden studies, Clausen et al. (1948) performed a reciprocal-transplant study based on a desire to understand the extent to which plasticity versus genetic differentiation (i.e., adaptation) contributed to the fluidity of forms seen within a single species across environments (Nunez-Farfan and Schlichting 2001). However, this tried-and-true empirical approach, while a gold standard for revealing local adaptation, places a limit on aspects of its study. Many organisms are difficult, if not impossible, to transplant without harm, and others are sufficiently long lived that adequate measures of fitness are hard for researchers to obtain. Notably, Turesson, Clausen, Keck, and Hiesey worked with herbaceous, flowering plants, which are easily grown, relatively short-lived, and also often exhibit easily observed and measureable quantitative phenotypic variation.

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