Abstract
The obligate mutualism and exquisite specificity of many plant-pollinator interactions lead to the expectation that flower phenotypes (e.g., corolla tube length) and corresponding pollinator traits (e.g., hawkmoth proboscis length) are congruent as a result of coevolution by natural selection. However, the effect of variation in flower morphology on the fitness of plants and their pollinators has not been quantified systematically. In this study, we employed the theoretical morphospace paradigm using a combination of 3D printing, electronic sensing, and machine vision technologies to determine the influence of two flower morphological features (corolla curvature and nectary diameter) on the fitness of both parties: the artificial flower and its hawkmoth pollinator. Contrary to the expectation that the same flower morphology maximizes the fitness of both plant and pollinator, we found that the two parties have divergent optima for corolla curvature, with non-overlapping fitness peaks in flower morphospace. The divergent fitness optima between plants and pollinators could lead to evolutionary diversification in both groups.
Highlights
Plant-pollinator interactions are considered to be classical examples of mutualism [1]
Contrary to the expectation that a single flower morphology maximizes the fitness of both plant and pollinator, we found that the two parties have divergent optima, with non-overlapping fitness peaks in flower morphospace
In the second stage experiments, we focused on flower-hawkmoth interaction in the region of flower morphospace identified in the first stage as most sensitive to variation in corolla curvature (c) and nectary diameter (2r0)
Summary
Plant-pollinator interactions are considered to be classical examples of mutualism [1]. Flower traits are expected to be congruent with the corresponding phenotypes of their pollinators, in obligate mutualisms where each party is completely dependent on the other for survival and reproduction. A striking example of this congruence is Darwin’s famous prediction of the existence of a hawkmoth species with a long proboscis to match the extraordinarily long nectar spur of a Malagasy orchid [6]. Such precise, predictable phenotypic matching between flower and pollinator morphologies suggests that flower shape is optimized by coevolution to maximize the fitness of both the plant and the pollinator, but this hypothesis has never been explicitly tested in a comprehensive way, partly.
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