Reproductive success over Calliandra fasciculata Benth. floral anthesis: evidence of adaptive generalization

Interactions between plants and pollinators are shaped by floral traits, and the combination of these characteristics determines the level of specialization in pollination systems. Plants with generalist systems are expected to exhibit less restrictive traits and receive similar contributions from different visitors to their reproduction. For instance, greater floral longevity may enhance pollination by a wider range of visitors, leading to generalization. In this study, we investigated the pollination dynamics (floral visitors, changes in traits, reproductive success) along the floral longevity of Calliandra fasciculata in the Brazilian Campos Rupestres (rocky outcrops). The species has brush-shaped flowers, produces nectar, and changes color during anthesis. It was visited by hummingbirds and bees during the day, and by bats and hawkmoths at night. Flower color and nectar secretion changed synchronously during anthesis. High nectar production at night, when flowers are white and absorb UV, led to a higher frequency of visits than during the day. However, polyad removal and deposition on stigmas remained high throughout the floral lifespan, indicating that both diurnal and nocturnal pollinators contribute to pollination. Yet, fruit and seed production were consistently low, suggesting nutritional limitation. Our results indicate that extended floral longevity is associated with increased generalization in the pollination system of C. fasciculata. The comparable contribution of day and night pollinators suggests adaptive generalization, in which floral traits are linked to broader visitor diversity and enhanced reproductive success.