Plant, Animal & Microbe Genomes X Conference

January 12-16, 2002
Town & Country Convention Center
San Diego, CA

Workshop: Compositae
            

TRANSGRESSIVE SEGREGATION, ADAPTATION, AND SPECIATION

¹ Department of Biology, Indiana University, 1001 E. Third Street, Bloomington, Indiana 47405 USA

Entry into new and discrete ecological niches is theoretically difficult because it often requires simultaneous changes at multiple traits. One possible mechanism by which this difficulty might be overcome is transgressive segregation, which refers to the generation of extreme traits in segregating hybrid populations. Transgressive segregation is observed for many traits in artificial hybrids, and some authors have suggested that it might contribute to adaptation in nature. In annual sunflowers, the three wild species found in the most extreme habitats (sand dunes, desert floor, and salt marshes) all happen to be of hybrid origin. Possibly, transgressive segregation contributed to niche colonization. This hypothesis was tested by assessing whether (1) synthetic hybrids exhibited the transgressive phenotypes thought to be necessary for colonization of sand dune, desert floor, and salt marsh habitats; (2) transgressive phenotypes were favored by selection in nature; and (3) QTL combinations contributing to transgressive phenotypes in synthetic hybrids also occurred in the natural hybrid species. Results indicate that extreme traits found in natural hybrid species can be accounted for by transgressive segregation, that the transgressive phenotypes are under strong directional selection in hybrid habitats, that transgressive segregation in wild species is largely due to complementary gene action, and that transgressive QTL combinations in synthetic hybrids are found in the natural hybrid species. Thus, transgressive segregation likely facilitated major ecological transitions in annual sunflowers.