Pollination and reproductive success of two colour variants of a deceptive orchid, Dactylorhiza maculata (Orchidaceae)

Polymorphism in petal colour is common in deceptively pollinated plant species. Most of the deceptively pollinated orchids are food frauds, and in most of them, the deception is not mimetic. These plants have conspicuously coloured flowers which they use as the main attractant of naive pollinators. In a field experiment, we studied the response of bumblebees and other types of flower visitors to colour differences between experimentally paired plants of Dactylorhiza maculata , a nectarless food-deceptive species. In addition, pollen removal, an estimate of male fitness, and fruit production, an estimate of female fitness, were measured in the two colour variants. We found a trend of bumblebee preference for the dark-coloured flowers, but other flower visitors (as a group) showed no preference for any colour variant. No difference was found in the reproductive success between the two colour variants of D. maculata. The lack of a difference in reproductive success between plants with pale and dark inflorescences, despite the observed trend of bumblebee preference for dark inflorescences, suggests that there is some balancing factor in the pollination of the pale inflorescences. An excess of visits by some nocturnal species (or a group of species) which favours the pale colour of D. maculata inflorescences or an excess of visits during day time by some flower visitors other than bumblebees preferring the pale inflorescences over dark ones may form such a balancing factor.