Geographic patterns in pollinator visitation and pollination ecotypes in Claytonia virginica
The community of floral visitors for a plant species often shows extensive variation across the plants’ geographic range, and this variation may influence the value of each pollinator to plant reproductive success. Claytonia virginica is visited by a pollen-specialist bee Andrena erigeniae and a bombyliid fly Bombylius major. While the two are equally effective at pollen deposition, Andrena erigeniae removes and consumes a great deal of Claytonia virginica pollen, while Bombylius major does not. In those geographic areas in which there is high visitation by Andrena erigeniae, visits by the pollen-specialist may negatively affect Claytonia virginica reproductive success. In response, Claytonia virginica may adapt to the high pollen removal rates of Andrena erigeniae through the modification of plant traits, forming “pollination ecotypes”.
Sites in Maryland and Pennsylvania have much higher visitation by the specialist Andrena erigeniae, while sites in North Carolina have lower visitation by the specialist Andrena erigeniae and higher visitation by the bombyliid fly Bombylius major. Consistent with differences in pollinator populations, the rate of depletion of pollen in plant populations varies between states. Our data also show geographic variation in plant traits, which could be interpreted as responses to high removal rates by the specialist Andrena erigeniae. There are significantly more pollen grains in unvisited flowers in Maryland and Pennsylvania than there are in North Carolina, and the rate of anther dehiscence is slower in Maryland and Pennsylvania than it is in North Carolina. These responses may indicate the formation of pollination ecotypes in Claytonia virginica as a result of selection by the pollinator community.