Adaptive Divergence in Sunflowers

AbstractAnnual sunflowers have been developed into a model system for the study of adaptation, hybridisation and speciation. Various species and populations have adapted to a wide range of extreme habitats, including salt marshes, sand dunes, desert floor and agricultural environments. In many cases, the process of adaptation has been facilitated by hybridisation between distinct species. Population genetic analyses of several species have revealed evidence of natural selection at loci potentially associated with adaptation to different environments, and genomic analyses indicate that the signature of adaptive divergence is found throughout the genomes of these species. In some cases, the genetic architecture of reproductive isolation and species differences may facilitate adaptive introgression and the formation of new hybrid species through adaptive ecological divergence.Key Concepts:Hybridisation has played an important role in adaptation in sunflowers, both through adaptive introgression and through the formation of adaptively divergent hybrid species.Evidence for adaptive divergence in sunflowers comes from a number of sources, including field experiments, genetic mapping of adaptive traits and DNA sequence analyses.The early morphological and ecological divergence of hybrid species can be experimentally replicated under environmental conditions similar to those encountered by the hybrid species in nature, providing strong evidence that it is adaptive.Data from a number of sunflower species support the hypothesis that adaptive divergence is associated with large population size.