Pollen Heteromorphism in Thalictrum (Ranunculaceae)
To transmit sperm nuclei to the ovules (e.g. for fertilization to occur), pollen must arrive on the female's stigma and then germinate a pollen tube. Germination usually occurs through an aperture, a thinning in the pollen grain wall. Some flowering-plant species display pollen heteromorphism where each individual produces multiple different types of pollen with different numbers of apertures.
The number of apertures on a pollen grain can influence it's efficacy in different ecological and competitive scenarios. For instance, pollen grains with more apertures may germinate faster and be more successful at fertilizing ovules (especially in insect-pollinated species where pollen competition is intense). However, higher aperture numbers may reduce the longevity of a grain (which could be important in wind-pollinated species).
In environments that vary unpredictably, we might expect to see pollen heteromorphism as a "bet-hedging" strategy to ensure some successful fertilization in all conditions.
I have found significant pollen heteromorphism among species of Thalictrum, but phylogenetic comparative methods indicate that minimal correlations between pollen grain morphology and pollination mode.
Future Plans:
I have several projects planned to further our understanding of pollen heteromorphism (and how pollen morphology may respond to selective pressures) in natural populations.
