Geographical patterns of coevolution in a pollination mutualism.
Anderson, Bruce*,1, Johnson, Steve1, 1 University of KwaZulu-Natal, Pietermaritzburg, South Africa
ABSTRACT- Darwin famously predicted the existence of a moth with an astonishingly long proboscis as the pollinator of the long spurred Madagascar Star Orchid. He proposed that extreme characteristics of these species evolved as a result of a coevolutionary arms race. Although frequently used as a text book example of coevolution, this moth has yet to be observed pollinating the Star Orchid! In fact there are very few well documented studies suggesting coevolution in pollination mutualisms. We focussed on a small guild of plants pollinated by a single long tongued fly species. We analyse a pair of adaptive morphological traits (fly proboscis length and floral tube length) which most likely coevolved under an arms race scenario as envisaged by Darwin. The fly has a wide distribution and its proboscis length varies between populations. This variation is in turn closely matched by the floral tube lengths of the plants that it pollinates. For one widespread plant species we suggest that coevolution has driven the close match between proboscis and corolla tube. However for some plants such as deceptive orchids, correlated traits could only have arisen through trait tracking.
Key words: coevolution, Geographic mosaic, pollination, mutualism
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