SCHWARZBACH, ANDREA E.* AND LOREN H. RIESEBERG. Department of Botany, Indiana University, Bloomington, IN 47405. - Multiple origins of a diploid hybrid species.
Helianthus anomalus is a well characterized diploid hybrid
species occurring in several geographically isolated sand dune
habitats in Utah and Arizona. The parental species H. annuus
and H. petiolaris can be found in the same area but show
different habitat preferences. Helianthus annuus prefers heavy
clay soils whereas H. petiolaris can be found on drier sandy
soils. Endemic dune species often are characterized by avoidance of
long-distance dispersal. Helianthus anomalus displays many
characters that seem to follow this rule, e.g. large achene weight and
non-shattering of fruits. We conducted a phylogeographic study to
reconstruct the historical biogeography of this dune species and we
also examined the possibility of recurrent hybrid origin using
cpDNA-CAPS and nuclear SSR markers. At least seven populations of each
species and 12 individuals per population were sampled and a haplotype
tree was reconstructed. Our molecular data support poor long-distance
dispersal capabilities and suggest several independent origins of the
hybrid species H. anomalus on different dune systems.
Key words: Helianthus, hybridization, multiple origin, phylogeography