Papilio butterfly vs. hawkmoth pollination explains floral syndrome dichotomy in a clade of Lilium

Pollination niche shifts can drive remarkable floral divergence between closely related plant species. The Leucolirion clade of Lilium contains species with either tepal-recurved or trumpet-shaped flowers. The tepal-recurved flowers are bright orange and might be pollinated by butterflies and/or birds. The trumpet-shaped flowers are mostly pale and strongly fragrant and might permit visitation by a variety of hawkmoths. Lilium leucanthum has trumpet-shaped flowers, and some populations of this species show dark coloration on the floral outer surface, suggesting pollination by mammals. We identified pollinators and examined the dependence of reproduction on pollinators by floral visitor observations, pollen load analysis and pollination experiments. We also analysed floral traits to contrast the two floral syndromes involving different lepidopteran groups. The tepal-recurved lilies are specialized on a group of Papilio butterflies for pollination with pollen predominantly attached to the hindwings. The trumpet-shaped flowers are almost exclusively pollinated by hawkmoths, including diverse species with proboscises of different lengths. No mammal visitation was found to the populations of L. leucanthum with dark outer surfaces of flowers. Self-incompatibility prevails throughout the clade, including the populations in which pollinators were scarce. The butterfly- and hawkmoth-pollinated species display contrasting floral syndromes. Our findings confirmed that the dichotomy in floral syndrome in the Leucolirion clade is associated with Papilio butterfly vs. hawkmoth pollination, whereas intraspecific variation in colour of the floral outer surface of L. leucanthum many need a non-pollinator explanation.