Müllerian mimicry between oil-producing orchids and Malpighiaceae? An old hypothesis finally tested.

The concept of mimicry has been developed for animals, but it also applies to plants. Plant species may be Müllerian mimics if they have similar reproductive traits and offer similar rewards to the pollinators. Several Oncidiinae orchids offer floral oils to their pollinators and have been suggested to form a Müllerian complex with species of Malpighiaceae. We provide a test of this hypothesis using Gomesa flexuosa (Orchidaceae) and Janusia guaranitica (Malpighiaceae), which are sympatric and phenologically synchronous, secrete the same floral resource (oils), and show similar flower morphology. We exposed individuals of Gomesa near and far from individuals of Janusia and monitored floral visitation. Both species were exclusively pollinated by oil-collecting bees, sharing Centris trigonoides as a pollinator. Nevertheless, the probability of bee visitation, number of contact approximations, and number of visits to flowers of Gomesa were similar when individuals were near and far from Janusia. These findings do not support the Müllerian mimicry hypothesis in these two species. Their resemblances can be better explained by the "exploitation of perceptual biases" hypothesis. According to this hypothesis, pre-existing traits in Oncidiinae orchids (e.g. colour, shape, rewards) may coopt oil-collecting bees that usually search for rewards in Malpighiaceae species with similar flower traits.