Natural selection ideally results in organisms that are well-adapted to their environments. However, such fine-tuning is difficult to attain for species that live over a broad range of environmental conditions. Emigration from the center of the species range to the margins can introduce genes that are suited for environments at the center but maladapted for environments at the periphery. The counteracting forces of natural selection and gene flow will be investigated for a plant species that ranges from sea level to 1500 meters elevation on the Pacific Slope in Costa Rica. Replicate gardens will be established across the range of elevations, using plants that originate from across the range, whose biological fitness will be evaluated in each environment. A 'home field' advantage provides evidence that natural selection has promoted different genes at different sites. In a second set of experiments, molecular markers will be used to estimate the amount of gene flow across the elevational range of the species.
The project addresses a central question in population biology, the extent to which gene flow counteracts natural selection. It takes place in montane tropical forests, providing conservation relevance and a useful comparison to results from temperate systems. Training opportunities will be provided for at least eight undergraduate and three post-baccalaureate students.
