Epiphyte Vanilla relies on birds as long-distance seed dispersers.

Abstract

Angiosperms comprise the most diverse group of land plants. While essentially sessile organisms, flowering plants can disperse their genes through pollen flow and expand their occurrence range by means of seed dispersal. While most orchids are anemophilous, seed dispersal in Vanilla is mediated by vertebrates. Here, I investigate processes involved in the attraction and rewarding of seed dispersers of an obligatory epiphytic Vanilla through field observations, analysis of fruit morphology, resource production, fragrance release, and seed viability. Dehiscent fruits of Vanilla lindmaniana are attractive exclusively to birds. The fruit cavity contains a mucilaginous substance rich in sugar, fat, protein, and starch, which is consumed by several bird species. The basal cells of the funiculi contain calcium oxalate crystals, which are harmful to mammals. Seed viability testing revealed that seeds germinate after passing through the bird digestive tract. This is the first study describing an obligatorily ornithochorous Vanilla. A mucilaginous substance produced by Vanilla fruits is consumed by diurnal birds, corroborating fruit features compatible with ornithochory. The presence of raphides in the funiculi cells also confirms that seed dispersal of V. lindmaniana is mediated exclusively by birds. Ornithochory is pivotal in the effective dispersal of seeds in obligate epiphytic Vanilla, as it ensures that consumed seeds are taken to other phorophytes through avian faeces, allowing gene flow and the colonization of new areas and environments.