Print PageOutcrossing with the help of coexistent specialist pollinators seems to be a good strategy for plants but a strong disadvantage when colonizing new territories that lack them. Example of the former, species of the genus Physalis serve as model systems for self-incompatibility and have been reported to rely primarily on specialist pollen-collecting bees. Nevertheless, at least three annual species (P. angulata, P. pubescens, and P. grisea) show greatly reduced flower size, a trait commonly associated with self-pollination, and two of them are known to occur in the absence of the two bee genera that include specialists to Physalis. In a greenhouse and common garden experiment, we tested for changes in floral morphology (stigma-anther distance), a decrease in the production of floral rewards (pollen and nectar), and changes in the frequency of pollinator visitation to annuals in the presence of two perennial, outcrossing congeners (P. heterophylla, P. longifolia).
Results/Conclusions
We found annual species had reduced stigma-anther separation, produced less pollen per flower, and were self-pollinating in the absence of pollinators (62-77% fruit set). Nectar production and visitation by pollinators were similar for annuals and perennials. However, the specialist visited perennials more frequently while annuals compensated the reduction with an increase in generalists. Thus, the annuals appear to be capable of taking advantage of generalist pollinators for outcrossing while relying on self-pollination to assure seed production.
