The importance of flower visitors not predicted by floral syndromes

Abstract

Flower visitors that do not fit a perceived floral syndrome are often over-looked and deemed unimportant. In Tritoniopsis revoluta, an irid with a very long corolla tube conforming to the long proboscid fly pollination syndrome, we determine visitation rates of bees and long proboscid flies, as well as ascertain whether bees could be important pollen vectors in this system. We confirmed the presence of extremely long proboscid Prosoeca longipennis flies in one T. revoluta population, but found that fly visitation was absent in most populations. Instead, we found that in the absence of flies, nectar wells up the corolla tubes and becomes accessible to Amegilla bees, which were the most frequent visitors to T. revoluta at most sites and carried pollen, suggesting they could effect pollination. The highest bee visitation rates were in T. revoluta populations with unusually short tubed plants, where nectar was more accessible than in plants with long corolla tubes. Short tubed populations with more bee activity had higher average seed set than long tubed populations, suggesting that bees might contribute significantly to fitness in this apparently long-proboscid fly pollinated plant. Although these results do not support the use of syndromes for predicting all of a flower's important pollinators, they do support the idea that floral morphology will be shaped by the most effective pollinators at the time.