The association of fly pollination and the dioecious breeding system in flowering plants: an empirical examination

Abstract

Dioecy is relatively uncommon among flowering plants, occurring in just 6% of species. It is associated with a suite of ecological characters whose role in breeding-system evolution is poorly known. I therefore explored the role of one correlate; generalist fly pollination. Flies acted differently than more specialized pollinators in their visits to plants, by revisiting flowers frequently and not discriminating between the sexes. In comparing dioecious and hermaphroditic species, I found that dioecious species had lower pollen transfer efficiency and pollen receipt, similar pollen removal and seed set, and higher fruit set than hermaphroditic species. Flies produced variance in reproductive characters, such as pollen removal and receipt, equaling that found in hermaphrodites, which should allow dioecious plants to compete effectively with hermaphrodites. Because flies visit plants differently than most other pollinators, their behaviour results in pollination attributes that could promote the evolution and maintenance of dioecy in some plant species.