Exploring the role of transgressive segregation in the origin of novel adaptation in a wild sunflower hybridspecies (Helianthus paradoxus)

Speciation is often driven by major ecological transitions, but the genetic mechanisms underlying such ecological shifts are poorly understood. One plausible mechanism is transgressive segregation, i.e., the generation of extreme phenotypes in the course of hybridization between divergent plant populations or species. Wild annual sunflowers (Helianthus spp.) provide an excellent model system for studying transgressive segregation and the origin of novel adaptation by hybridization. This project will focus on the evolution of salt tolerance in the sunflower hybrid species Helianthus paradoxus. The proposed work is based on results obtained during my first Schroedinger year (grant J1960-Bio). My aim is to assess the fitness effects of individual genomic regions (QTLs; quantitative trait loci) in early generation hybrids transplanted into natural H. paradoxus "hybrid" habitat, using flanking molecular markers as surrogates. lf transgressive segregation played an important role in the evolution of salt adaptation in this sunflower hybrid species, then the underlying QTLs should confer a selective advantage in the wild. Moreover, I plan to assess the fitness effects of candidate genes associated with salt tolerance, using novel sequence information for Helianthus spp. provided by a functional genomics consortium. The proposed experiments will allow me to study the action of the creative evolutionary force underlying the origin of this novel adaptation, natural selection, on individual QTLs and even on the actual "speciation genes" thought to be responsible for this hybrid speciation event.