Sapromyiophily in the native orchid, Bulbophyllum variegatum, on Réunion (Mascarene Archipelago, Indian Ocean)

Abstract : Orchid species are well known for their highly specialized pollinator interactions. To better understand the reproductive biology of the tropical epiphytic orchid Bulbophyllum variegatum on Réunion, we investigated the floral morphology, breeding system, pollinator diversity, floral scent profile and fruiting success of about 30 individuals in three natural populations during two consecutive flowering seasons. Controlled hand-pollination experiments in two populations showed that the species is self-compatible, but requires pollinator service to achieve reproduction. Videotape pollinator observations were conducted during two flowering seasons for 56 h and revealed that B. variegatum is pollinated by a single species of fly from the Platystomatidae. This fly seems to be attracted by the unpleasant scent produced by the flowers, and does not receive any reward after achieving pollination. In addition, no egg-laying behaviour was observed. Bulbophyllum variegatum thus exhibits a typical sapromyiophilous pollination syndrome which constitutes the first proven case of sapromyiophily within the genus Bulbophyllum on the Mascarene Archipelago. Hand pollinations further showed that fruit set was not significantly higher for flowers that received outcross pollen than for those that were self-crossed (53% and 44% respectively). Fruit sets under natural conditions were significantly different among populations, ranging from 0.5% to 24.3%. This low fruit production is likely due to infrequent pollinator visits, particularly in disturbed forests where the pollinator has never been observed.