Mixed Bat-Hummingbird Pollination Assures Reproductive Success in a Highly Variable Upper Montane Species

Callianthe sellowiana is a high-altitude species endemic to the Atlantic Forest that exhibits floral traits overlapping between ornithophily (hummingbird pollination) and chiropterophily (bat pollination), with highly variable flower color and shape and a yet unstudied reproductive system. We conducted observations and experiments in the upper montane Brazilian Atlantic Forest (2000 m a.s.l.), which revealed that both bat and hummingbird pollinators contribute similarly to fruit and seed set, with no significant difference between diurnal and nocturnal exclusion treatments. However, combined pollination yielded higher reproductive success, indicating functional complementarity and equal pollination effectiveness. Floral traits match both pollinators, with wider corollas at night aiding bat access and enhancing acoustic signals and narrower corollas during the day facilitating hummingbird pollination. Spectral analyses revealed low UV reflectance with a peak in red wavelengths, and for most phenotypes high green reflectance, matching both bat and hummingbird visual systems. While hummingbird visitation remained stable across flowering seasons, bat visitation was highly variable, suggesting that C. sellowiana maintains a stable bimodal pollination strategy. Furthermore, pollen tube growth experiments showed that small amounts of cross-pollen are sufficient to promote successful pollen tube development, even in the presence of self-pollen. These findings reveal a strategy that may mitigate self-pollen interference in a self-incompatible species. Our results highlight the ecological importance of functional and temporal complementarity in bimodal pollination systems and underscore how mixed pollination strategies may enhance reproductive success and resilience in diverse pollinator environments.