Vertebrate Pollination and the Maintenance of Dioecism in Freycinetia

Abstract

The hypothesis that pollination by large, nonnectivorous vertebrates can in some cases favor the evolution of dioecism was explored through a series of surveys and experiments with Freycinetia reineckei, a dioecious liana in Samoa, which is primarily pollinated by the flying fox Pteropus samoensis and the starling Aplonis atrifuscus. Staminate and bisexual inflorescences were found to face a far higher probability of destruction than pistillate inflorescences. Although destruction of staminate spikes is not deleterious to the fitness contribution of staminate spikes since the pollen is carried on the bat's face or bird's feathers, destruction of the bisexual spike is deleterious since the investment in gynoecial structures is forfeited. The data from the study were found to generate a concave fitness set, indicating that dioecism rather than hermaphroditism is an evolutionarily stable strategy. The relevance of these findings to other taxa is briefly discussed.