Bee pollination of the endangered orchid Calanthe discolor through a generalized food-deceptive system

Abstract

Calanthe discolor is a Japanese terrestrial orchid that is cultivated for its beautiful flowers arranged in racemose inflorescences. Although its propagation for horticultural purposes has been studied extensively resulting in the successful production of seedlings, little is known about the pollinators and breeding system of C. discolor in its natural habitat. The current study, which combined field observations and pollination experiments, was conducted to gain further insight into the reproduction of this important orchid species. Three bee species: Eucera nipponensis, Osmia cornifrons and Apis cerana japonica, were found to be effective pollinators, transferring the pollinaria on their heads. Pollination experiments also revealed that this species was self-compatible, although it was neither autogamous nor apogamous. The fruit set for the open-pollinated flowers was less than 10 %, suggesting a high degree of pollinator limitation, possibly as a result of the deceptive nature of this species. These results provide evidence that pollinator specificity is the primary mechanism of reproductive isolation between C. discolor and its close relative Calanthe striata, because the latter species is known to be exclusively pollinated by carpenter bee.