These plant-pollinator interactions are predicted to be the products of coevolution between plants and insects 4, 5. Angiosperms produce flowers with nectar and ample pollen to attract flower-visitors in return, the flower-visitors transport pollen and effect pollination, so producing seeds. Pollination is one of the commonest forms of mutualism between plants and animals 1, 2, 3, 4.

Our results suggest that a fine-tuned one-to-one coevolutionary state between a flower species and a pollinator species might be common, but frequently overlooked, in multiple flower-pollinator interactions. Behavioral observations also confirm the precision of this mutualism. Detailed morphology of the bee proboscis is shown to be finely adjusted to the floral morphology and nectar production of the flower. We here describe a fine-tuned coevolutionary state of a flower-visiting bee that collects both nectar and pollen from an early spring flower visited by multiple pollinators. Many insect pollinators are, however, considered generalists, visiting numerous kinds of flowers and many flower species (angiosperms) are also considered generalists, visited by many insect pollinators. Fine-tuned adaptations are usually found in the form of strict one-to-one coevolution between species. Relationships between flowers and pollinators are generally considered cases of mutualism since both agents gain benefits.

Hidden flowers