Adaptations between Ecotypes and along Environmental Gradients in Panicum virgatum*

Determining the patterns and mechanisms of natural selection in the wild is of fundamental importance to understanding the differentiation of populations and the evolution of new species. However, it is often unknown the extent to which adaptive genetic variation is distributed among ecotypes between distinct habitats versus along large-scale geographic environmental gradients, such as those that track latitude. Classic studies of selection in the wild in switchgrass, Panicum virgatum, tested for adaptation at both of these levels of natural variation. Here we review what these field experiments and modern agronomic field trials have taught us about natural variation and selection at both the ecotype and environmental gradient levels in P. virgatum. With recent genome sequencing efforts in P. virgatum, it is poised to become an excellent system for understanding the adaptation of grassland species across the eastern half of North America. The identification of genetic loci involved in different types of adaptations will help to understand the evolutionary mechanisms of diversification within P. virgatum and provide useful information for the breeding of high-yielding cultivars for different ecoregions.