Coevolution Between Food-Rewarding Flowers and Their Pollinators |
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Authors: | Steven D Johnson Bruce Anderson |
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Institution: | (1) School of Biological and Conservation Sciences, University of KwaZulu-Natal, P. Bag X01, Scottsville, Pietermaritzburg, 3209, South Africa;(2) Department of Botany and Zoology, University of Stellenbosch, P. Bag. X1, Matieland, Stellenbosch, 7602, South Africa |
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Abstract: | The concept of coevolution was first developed by Darwin, who used it to explain how pollinators and food-rewarding flowers
involved in specialized mutualisms could, over time, develop long tongues and deep tubes, respectively. He famously predicted
that Angraecum sesquipedale, a long-spurred Malagasy orchid, must be pollinated by a hawkmoth with an exceptionally long tongue. Darwin’s idea of a coevolutionary
“race” was championed by contemporary naturalists, including Alfred Wallace, and a hawkmoth fitting the expected tongue-length
profile was eventually discovered in Madagascar during the early twentieth century. However, strong empirical support for
the mechanism behind Darwin’s coevolutionary model has been forthcoming only in the past two decades. It is now established
that selection often strongly favors plants with floral tubes that exceed the length of their pollinator’s tongues. There
is also evidence that pollinators gain an energetic benefit from having tongues that enable them to consume most or all of
the nectar in deep tubular flowers. Alternative explanations for the evolution of long pollinator tongues, such as evasion
of predators that use flowers as ambush sites, are considered much less compelling and lack quantitative support. Another
important advance in coevolution research has been the development of approaches that explicitly predict a geographical mosaic
of coevolution. The expectation that coevolution can lead to geographical diversification and trait covariation among strongly
interacting organisms is strongly supported by studies of long-proboscid fly and oil-bee pollination systems in South Africa.
Macro- and microevolutionary studies of pollination systems suggest that coevolution can operate alongside other one-sided
evolutionary processes, such as shifts, in shaping plant and pollinator traits. |
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