BAACK, ERIC J. Center for Population Biology, University of California Davis, One Shields Ave, Davis, CA 95616. - Barriers to reproductive success of tetraploid snow buttercups (Ranunculus adoneus) due to interference from diploid plants.
Polyploid speciation has played a significant role in the production
of flowering plant diversity. Despite its importance, several aspects
of the ecology of the speciation process remain poorly understood.
Reproductive interference from surrounding diploid plants is thought
to be a major factor limiting the establishment of novel tetraploid
populations of outcrossing plants. In this study I examined barriers
reproduction in snow buttercups (Ranunculus adoneus:
Ranunculaceae). I conducted hand pollinations in the field using
plants from diploid or tetraploid buttercup populations. I compared
seed mass and number among cross-ploidy, within-ploidy, and mixed
ploidy pollinations to assess the potential barriers to tetraploid
reproduction when in a diploid population, and scored the ploidy of
the resulting seeds by flow cytometry. Cross-ploidy crosses resulted
in fewer, lighter seeds than within-ploidy crosses, indicating an
incomplete barrier to the formation of triploids. Mixed ploidy
pollinations using both tetraploid and diploid plants as pollen donors
produced fewer seeds but of the same mass as the within-ploidy
crosses, indicating that cross-cytotype pollen interfered with
fertility when within-cytotype pollen was present. Flow cytometry
revealed that the seeds resulting from mixed-ploidy crosses were
largely diploid (for diploid dams) or tetraploid (for tetraploid
dams), not triploid. This confirms that interference from cross-ploidy
pollinations could decrease the fitness of tetraploid plants in mixed
populations.
Key words: Ranunculus adoneus , flow cytometry, pollination, Polyploidy, reproductive barriers