POTENTIAL FOR THE LOSS OF SELF-INCOMPATIBILITY IN POLLEN-LIMITED POPULATIONS OF MAYAPPLE (PODOPHYLLUM-PELTATUM)

Self-compatibility (SC) appears to be a derived trait in many unrelated taxa. A major selective force that could lead to the evolution of SC from self-incompatibility (SI) is inadequate pollination. Here we show that seed set is strongly pollen-limited in populations of mayapple, Podophyllum peltatum (Berberidaceae). Hand-pollination led to a 26-fold increase in seed set as compared to natural levels in 1989, and to a fivefold increase in 1990. The species is SI, but in a survey of 49 colonies in Ohio we found three that had more than 50% fruit set from self pollen (as compared to about 90% fruit set from hand-outcrossed flowers). However, when hand-selfing yielded fruits, the number of seeds per fruit was only about 10% of the seed set from hand-outcrossing. We discuss the relative fecundity of putative SC and SI genotypes in terms of conditions needed for the spread of SC in mayapple populations (little or no morphological change would be needed to ensure within-flower selfing). Seed set from putative SC genotypes appeared to be low enough to prevent them from replacing SI genotypes, even in the face of infrequent pollinator visits.