Simultaneously flowering species may exchange pollen, resulting in stigmatic interference, and avoidance of receipt of foreign pollen may select for the evolution of floral specialization. My research tests a central prediction of this hypothesis, namely that morphologically different flowers share less pollen. To study this, I have observed pollinators and isolated, identified, and counted pollen grains from many species of flowers with a range of morphologies from a diverse prairie invaded by Euphorbia esula , a species with an unrestrictive morphology. As hypothesized, flowers with unrestrictive morphologies share more pollinators with Euphorbia , and receive more pollen from this species, though differences in stigma size may account for some of the variation.

Effects of heterospecific pollen transfer
I am also interested in traits of recipient flowers that predict whether they experience harm from foreign pollen receipt. To investigate this, I have performed several studies in which I pollinated flowers with conspecific pollen only or Euphorbia pollen followed by conspecific pollen. Some species were negatively affected by this receipt, while others were not, and there is a tendency toward self-incompatible species being less affected than self-compatible species.

Working with Lynda Delph, my current research focuses on differential pollen tube growth rates as barriers to hybridization between closely related sympatric Silene species. Silene latifolia and S. dioica , co-occur and are easily hybridized, but few natural hybrids are found. I have found that conspecific pollen tubes grow faster than heterospecific pollen tubes, which could account for few hybrids being formed even when pollinators transport mixed pollen loads.

Costs of genes restoring male fertility for a plant with cytoplasmic male sterility
Working with Lynda Delph and collaborators Greg Brown and Maia Bailey on the cost of genes that restore male function in oil-seed rape, Brassica napus, which exhibits cytoplasmic male sterility. Costs associated with restorer genes are thought be one element preventing these genes from becoming fixed in populations, and consequently allowing the maintenance of gynodioecy as a mating system. By comparing fitness indicators in plant lines with or without the restorer alleles in a cytoplasmic background that allows all lines to express male and female traits, we will measure whether restorer genes result in plants with less reproductive output. This will help to isolate the role of cost of restoration in maintaining gynodioecy.  

See Lynda Delph; and Delph Lab Page for more information about the research going on in the Delph lab.