A preview of the PDF is not available
The Pollinators of the Malagasy Star Orchids Angraecum sesquipedale, A. sororium and A. compactum and the Evolution of Extremely Long Spurs by Pollinator Shift
Abstract: The pollination process of the extremely lang-spurred orchids Angraecum sesquipedale and A. sororium is described and documented here for the first time. The pollinaria and viscidia Ioad was examined in moths captured in central and south Madagascar. Visits to orchids by hawkmoths were rarely observed in the field and were therefore systematically recorded in !arge flight tents using a night-vision video technique and fla shlight photography. Angraecum sesquipedale in Fort Dauphin is pollinated by Xanthopan morgoni proedieta and A. sororium on Mt. Angavokely by Coelonia solani. By combining a deep nectar spur of extraordinary length with a protruding labellum functioning as a landing platform, these orchids overcome the moth's Stereotypie swing-hovering flight thus enabling full Insertion of the long tongue. Angroecum compaetum in Foret d'Ambohitantely is pollinated by both the shorter and longertongued forms of Ponogeno lingens which never swing-hover but is also exploited by X. morgani and C. solani with wastage of pollinaria. The duration of tongue Insertion, nectar exploitation and tongue withdrawal were analyzed: legitimate and illegitimate visito rs differ in their time budget and approach to the flower. Nectar volume, nectar Ievei and sugar concentration of A. sesquipeda/e and A. sororium were compared with the nectar requirements of the pollinating hawkmoths. The evolution of very long spurs in these orchids is likely to have involved a series of pollinator shifts. The orchids adapted to different hawkmoth species with increasingly long tongues which primarily evolved to avoid predator attacks during vis its to less specialized flowers. This "pollinator s hift" model modifies the dassical "coevolutionary race" model. The relevance of the taxon Angroecum bosseri Senghas is questioned.