Abstract
Charles Darwin correctly predicted the existence of an extraordinarily long-tongued hawkmoth in Madagascar, based on the length of the floral spur of an Angraecum orchid. This hawkmoth, Xanthopan morganii, is also the longest-tongued hawkmoth on the African mainland, but its ecological role as a pollinator has been virtually unknown outside of Madagascar. We investigated whether X. morganii pollinates Bonatea steudneri, an orchid with floral spurs that vary from 10 to 21 cm in length among populations. At a forest locality in central Kenya, we observed X. morganii individuals with tongues ca. 16 cm in length pollinating B. steudneri plants with spurs ca. 15 cm in length. At other localities in Kenya, we observed visits by the hawkmoths Agrius convolvuli (tongue c. 12 cm) and Coelonia fulvinotata (tongue ca. 10 cm). Pollinaria of B. steudneri are attached to the eyes of hawkmoth visitors. Flowers of B. steudneri show several adaptations for hawkmoth pollination, including anthesis at dusk and nocturnal emission of scent dominated by the volatile compound linalool. This study highlights the potential for predicting certain highly specialized interactions among species by matching of their respective morphological dimensions.
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Acknowledgements
We would like to thank Benny Bytebier and Daniel Odhiambo for logistical support and locating the orchid populations. Research was supported by the National Research Foundation of South Africa (MGB and SDJ). We would like to thank Ruth Cozien for help with analysis of nectar sugar composition in the laboratory. We also thank Ian Kitching for confirming the identity of Xanthopan morganii. Martins’ work on pollination in Kenya is supported by the Mpala Research Centre, Princeton University, National Geographic Society, Kenya Orchid Society and Whitley Fund for Nature. We thank the East Africa Herbarium and National Museums of Kenya for access to their collections.
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Online Resource 1. Bonatea steudneri spur length measurements and locality information from available herbarium specimens.
Online Resource 2. The relationship between nectar volume (µL) and nectar column height (cm) in flowers of Bonatea steudneri.
Online Resource 3. Non-metric multidimensional scaling (NMDS) based on the Bray–Curtis similarity matrices of Bonatea steudneri floral scent profile sampled at midday and at 19:00 h.
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Balducci, M.G., Martins, D.J. & Johnson, S.D. Pollination of the long-spurred African terrestrial orchid Bonatea steudneri by long-tongued hawkmoths, notably Xanthopan morganii. Plant Syst Evol 305, 765–775 (2019). https://doi.org/10.1007/s00606-019-01605-2
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DOI: https://doi.org/10.1007/s00606-019-01605-2