AOBPreview originally published online on March 22, 2006
Annals of Botany 2006 97(6):965-974; doi:10.1093/aob/mcl056
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Bird Pollination in an Angraecoid Orchid on Reunion Island (Mascarene Archipelago, Indian Ocean)
1 UMR 53 Peuplements Végétaux et Bio-Agresseurs en Milieu Tropical, Université de La Réunion, 15 avenue René Cassin, BP 7151, 97415 Sainte Clotilde Messag Cedex 9, La Réunion, France and 2 Herbier Universitaire de La Réunion, 15 avenue René Cassin, BP 7151, 97415 Sainte Clotilde Messag Cedex 9, La Réunion, France
* For correspondence. E-mail claire.micheneau{at}univ-reunion.fr
Received: 15 July 2005 Returned for revision: 9 September 2005 Accepted: 24 January 2006 Published electronically: 22 March 2006
• Background and Aims Although numerous angraecoid orchids in Madagascar display typical sphingophilous syndrome (i.e. white, nectariferous, long-spurred flowers, producing a strong scent at the crepuscule that is attractive to moths), three species of Angraecum in Reunion, belonging to the endemic section Hadrangis, have atypical unscented and short-spurred flowers. The aim of the study was to investigate the implication of plant–pollinator interaction on the evolution of floral morphology of these peculiar island floral forms.
• Methods The flower morphology of A. striatum (one of the three section Hadrangis species) was investigated by performing a set of floral measures, and the reproductive biology was investigated by a set of hand pollination experiments. Natural pollinators were observed by means of a digital video camera. Pollinator efficiency (pollen removal and deposition) and reproductive success (fruit set) were quantified once a week in natural field conditions during the 2005 flowering season (i.e. from January to March).
• Key Results The orchid is self-compatible but requires a pollinator to achieve fruit set. Only one pollinator was observed, the endemic white-eye Zosterops borbonicus (Zosteropidae). These birds perched on inflorescences, and probed most fresh-looking flowers on each plant for nectar. Nectar was both abundant (averaging 7·7 µL) and dilute (averaging 9·7 % sugar in sucrose equivalents). Birds were mostly active between 0830 and 0930 h. Visits to plants were extremely short, lasting from 9 to 27 s. At the study site, 60·9 % of flowers had pollen removed, and 46·4 % had pollinia deposited on stigmas. The proportion of flowers that initiated a fruit averaged 20·6 % in natural conditions.
• Conclusions For the first time, a bird-pollinated orchid is described from a sub-tribe that is mainly specialized for moth pollination. This study documents a morphological shift in flowers in response to pollinator adaptations in the insular context of the Mascarene Archipelago.
Key words: Angraecum striatum, bird pollination, Mascarenes, oceanic islands, Orchidaceae, Reunion, white-eyes, Zosteropidae
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