Investigating the effects of fire on pollinator-dependent distyly polymorphism.

Fire influences plant traits in several ways, but its effects on flower polymorphisms are unknown. Distyly, a floral polymorphism with long-styled (L-styled) and short-styled (S-styled) morphs exhibiting reciprocal herkogamy and a self-incompatibility system, depends on biotic pollination for intermorph pollination and reproduction. We investigated the effects of fire on the functioning of distyly, assessing morphology, floral reward, between-morph reciprocity, and reproductive success. We studied a population of the distylous hummingbird-pollinated Palicourea rigida (Rubiaceae) in the Brazilian savanna by comparing individuals from a fire-affected area with those from a contiguous unaffected area. Fire affected some floral traits, reducing the number of inflorescences (9.4%), corollas (4.7%), anthers (5.9%), and L-styled stigmas (33.5%). However, it did not affect plant height, number of buds and inflorescences, or nectar traits. Fire did not affect between-morph reciprocity. Hence, plants affected or not affected by fire presented similar reciprocity measures, translating into similar pollen deposition and fruit set of both morphs. Fire also had a morph-specific positive effect on the S-morph fruit set (35.31% increase). Fire can induce morphological changes in distylous species. However, fire does not influence most pollinator attraction and reward traits. The consistency of reproductive heights enables pollen flow within the fire-affected area and across the mosaic of different fire histories. The high resprouting ability linked to the rapid restoration of reproductive capacity allows distyly functioning through efficient intermorph pollen transfer. Such plant resilience may be important for maintaining the polymorphism and the associated pollinators under increasingly frequent anthropogenic fires.