LEXER, CHRISTIAN*, MARK WELCH, OLIVIER RAYMOND, and LOREN H. RIESEBERG. Biology Department, Indiana University, Bloomington, IN 47405. - Towards understanding the role of transgressive segregation in adaptation.
Transgressive segregation provides a simple and plausible explanation
for the niche divergence and phenotypic novelty often associated with
plant hybrid lineages. QTL studies in numerous plant species indicate
that transgressive segregation is frequent in plants, and that it is
an expected consequence of the genetic architecture of differentiated
populations or species. However, existing QTL studies of transgressive
traits in plants have not attempted to validate the fitness effects of
transgressive traits in natural habitats, nor have they measured the
effects of individual QTL alleles on hybrid fitness. Studies like this
may bridge the gap between transgressive segregation and the origin of
novel adaptation in nature. We are currently conducting field
experiments using synthetic hybrid lineages between Helianthus
annuus and H. petiolaris , the two sunflower species that
gave rise to H. paradoxus , the Pecos puzzle sunflower. Our
goal is to study the relationships between hybrid fitness and
transgressive traits associated with niche divergence (salt tolerance
in this model system). Ultimately, we plan to study the fitness
effects of individual QTL alleles in natural "hybrid
habitat". Preliminary results of these selection experiments will
be presented and discussed.
Key words: Helianthus , adaptation, fitness, QTLs, transgressive segregation