Meeting Abstract

S4.9  Monday, Jan. 4  Pollinarium ejection and the evolution of hypervariable male flowers in Catasetum orchids FULOP, D; KRAMER, EM; DUMAIS, J*; Harvard University jdumais@oeb.harvard.edu

Orchids possess an exquisite suite of characters to support pollination. Among the most remarkable of these characters is the forcible pollinarium discharge of the genus Catasetum. When ejected from a male flower, the pollinarium attaches precisely to the dorsum of the visiting bee, which will, upon visiting a female flower, deposit the pollen-bearing pollinia into the stigma, thus achieving pollination. The fast release of the pollinarium and precise targeting to the bee’s dorsum are critical for successful pollination in the genus; yet these features have received only limited attention in the literature. Here we show that the impulse that propels the pollinarium comes from the elastic energy stored in the stipe and that subsequent interaction with the flower column guides the pollinarium toward the bee. This active pollination mechanism stands in sharp contrast with pollination in the majority of orchid genera where floral architecture must ensure that the pollinator comes in direct contact with the static pollinarium. In Catasetum, the pollinarium guidance mechanism and remote triggering via the action of the antennae have relaxed this structural constraint in the design of flowers. This innovation, we propose, has enabled the exceptional diversification of male flower morphology in the genus. To support this claim, we show that one major axis of diversification – the degree of flower opening – correlates precisely with the key biomechanical parameter for pollinarium guidance. Our results give new insight into the evolutionary mechanisms behind the staggering morphological diversity found in orchids.