A tale of three morphs: nectar, reproductive compatibility, and morph abundance explain reproductive success within a...

Although floral colour polymorphism is common in angiosperms, the functional nature of polymorphic traits within a species remains poorly understood. Colour morphs may differ in traits other than colour, including nectar reward, pollinator visitation, and reproductive compatibility. We studied bract colour polymorphism in a nocturnal ginger, Curcuma caulina, to ask: (i) Do the nectar rewards, hawkmoth visitations, and reproductive compatibility differ among morphs? (ii) Do the morphs differ in their female reproductive success, and does this correlate with their observed abundance? We measured floral and vegetative traits in three dominant morphs and compared nectar rewards, nocturnal pollinator visitation rates, intra- and inter-morph compatibility, and natural fruit and seed production. The morphs did not differ in morphology but differed in their bract colour and within-population abundance. The common green-red morph has low-energy nectar, low pollinator visitation rates, and is self-incompatible, but has the highest reproductive success. The rare red-white morph, despite high-energy nectar, higher pollinator visitation rates, and a leaky self-compatibility, shows lower female reproductive success. Thus, the morphs have contrasting nectar traits, reproductive compatibility, and reproductive success. Path analyses indicated that nectar reward, pollinator visitation, reproductive compatibility, and abundance jointly explained variation in female reproductive outcomes, although their effects differed among morphs. These results show that bract colour morphs of C. caulina differ in multiple ecological and reproductive traits and provide a foundation for future studies testing male fitness, seedling survival, clonal structure, and abiotic selection.