GROSS, BRIANA L.1*, ANDREA E. SCHWARZBACH2, and LOREN H. RIESEBERG3. 1Biology Department, Willamette University, Salem OR 97301; 2Department of Biological Sciences, Kent State University, Kent OH 44242; 3Department of Biology, Indiana University, Bloomington IN 47405. - Potential multiple origins for Helianthus deserticola, a diploid hybrid species.
Homoploid hybrid speciation has traditionally been considered a rare
event, dependent on the establishment of both a novel, balanced
genotype and reproductive isolating barriers between the new species
and its progenitors. However, more recent studies have shown that
synthetic hybrids converge to match the chromosomal structure of
natural hybrids after only a few generations, suggesting that this
phenomenon may be more frequent than previously assumed. Here the
possibility that the diploid hybrid species Helianthus deserticola has
arisen from more than one hybrid speciation event was investigated
using chloroplast DNA PCR-RFLPs. The haplotypes present in eight
different populations of H. deserticola from locations spanning its
known geographical range were assayed based on four PCR amplified
fragments of chloroplast DNA, digested with a total of seven
restriction enzymes. The cpDNA haplotypes for H. deserticola were
compared to the haplotypes found in seven populations of the parental
species H. annuus and six populations of the parental species H.
petiolaris with the same geographic distribution. A total of eleven
different haplotypes were detected in the three different species;
seven of the H. deserticola populations had haplotypes characteristic
of H. petiolaris, while one had a haplotype characteristic of H.
annuus. This variation in cpDNA haplotype may be explained by a single
origin for H. deserticola followed by cytoplasmic introgression or by
multiple diploid hybrid speciation events. Microsatellite markers were
used to further investigate these two possibilities.
Key words: cpDNA PCR-RFLPs, Helianthus deserticola, homoploid hybrid speciation, hybridization, multiple origins