Premating isolation in neopolyploid red clover (Trifolium pratense)

Premise—Although polyploidy has been studied since the early 1900’s,
fundamental aspects of polyploid ecology and evolution remain unexplored.
In particular, surprisingly little is known about how newly formed
polyploids (neopolyploids) become demographically established. Models
predict that most polyploids should go extinct within the first few
generations due to reproductive disadvantages associated with being the
minority in a primarily diploid population (i.e., the minority cytotype
principle), yet polyploidy is extremely common. Therefore, a key goal in
the study of polyploidy is to determine the mechanisms that promote
polyploid establishment in nature. Because premating isolation will be
critical for neopolylpoids to avoid minority cytotype exclusion and thus
facilitate establishment, we examined floral morphology and three common
premating barriers to determine their importance in generating
reproductive isolation of neopolyploids from diploids. Methods—We induced
neopolyploidy in Trifolium pratense and compared their floral traits to
the diploid progenitors. In addition to shifts in floral morphology, three
premating barriers were examined: isolation by self-fertilization,
flowering time asynchrony, and pollinator mediated isolation. Results—We
found significant differences in the morphology of diploid and
neopolyploid flowers, but these changes did not facilitate premating
barriers that would generate reproductive isolation of neopolyploids from
diploids. There was no difference in flowering phenology, pollinator
visitation, or selfing between the cytotypes. Conclusions—Our results
indicate that barriers other than the ones tested in this study, such as
geographic isolation, vegetative reproduction, or pistil-stigma
incompatibilities, might be more important in facilitating isolation and
establishment of neopolyploid Trifolium pratense.