Search for: All records

Although polyploidy has been studied since the early 1900s, 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 as a result of 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 is critical in order 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.

We induced neopolyploidy inTrifolium pratenseand compared their floral traits to the diploid progenitors. In addition to shifts in floral morphology, we examined three premating barriers: isolation by self‐fertilization, flowering‐time asynchrony, and pollinator‐mediated isolation.

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.

Our results indicate that barriers other than the ones tested in this study—such as geographic isolation, vegetative reproduction, and pistil–stigma incompatibilities—may be more important in facilitating isolation and establishment of neopolyploidT. pratense.

Variation in pollen‐ovule ratios is thought to reflect the degree of pollen transfer efficiency—the more efficient the process, the fewer pollen grains needed. Few studies have directly examined the relationship between pollen‐ovule ratio and pollen transfer efficiency. For active pollination in the pollination brood mutualisms of yuccas and yucca moths, figs and fig wasps, senita and senita moths, and leafflowers and leafflower moths, pollinators purposefully collect pollen and place it directly on the stigmatic surface of conspecific flowers. The tight coupling of insect reproductive interests with pollination of the flowers in which larvae develop ensures that pollination is highly efficient.

We used the multiple evolutionary transitions between passive pollination and more efficient active pollination to test if increased pollen transfer efficiency leads to reduced pollen‐ovule ratios. We collected pollen and ovule data from a suite of plant species from each of the pollination brood mutualisms and used phylogenetically controlled tests and sister‐group comparisons to examine whether the shift to active pollination resulted in reduced pollen‐ovule ratios.

Across all transitions between passive and active pollination in plants, actively pollinated plants had significantly lower pollen‐ovule ratios than closely related passively pollinated taxa. Phylogenetically corrected comparisons demonstrated that actively pollinated plant species had an average 76% reduction in the pollen‐ovule ratio.

The results for active pollination systems support the general utility of pollen‐ovule ratios as indicators of pollination efficiency and the central importance of pollen transfer efficiency in the evolution of pollen‐ovule ratio.

Polyploidy is known to cause physiological changes in plants which, in turn, can affect species interactions. One major physiological change predicted in polyploid plants is a heightened demand for growth‐limiting nutrients. Consequently, we expect polyploidy to cause an increased reliance on the belowground mutualists that supply these growth‐limiting nutrients. An important first step in investigating how polyploidy affects nutritional mutualisms in plants, then, is to characterize differences in the rate at which diploids and polyploids interact with belowground mutualists.

We usedHeuchera cylindrica(Saxifragaceae) to test how polyploidy influences interactions with arbuscular mycorrhizal fungi (AMF). Here we first confirmed the presence ofAMFinH. cylindrica, and then we used field‐collected specimens to quantify and compare the presence ofAMFstructures while controlling for site‐specific variation.

Tetraploids had higher colonization rates as measured by total, hyphal, and nutritional‐exchange structures; however, we found that diploids and tetraploids did not differ in vesicle colonization rates.

The results suggest that polyploidy may alter belowground nutritional mutualisms with plants. Because colonization by nutritional‐exchange structures was higher in polyploids but vesicle colonization was not, polyploids might form stronger associations with theirAMFpartners. Controlled experiments are necessary to test whether this pattern is driven by the direct effect of polyploidy onAMFcolonization.