Integrating Biotic and Abiotic Factors to Elucidate Reproductive Success in Rafflesia zollingeriana Koord

Background and aims - The pollination mechanism of Rafflesia r emains a mystery due to its dioecious nature, as male and female flowers rarely bloom simultaneously in the same location. This study examined the reproductive biology of Rafflesia zollingeriana Koord., an endemic species of East Java, by analyzing flower morphology, phenology, and pollen viability, alongside field observations on microclimate conditions and pollinator visitation.

Material and methods - Pollen samples were collected every six hours, stained with 1% TTC solution, and examined using a Dinolite microscope, while morphological analysis was performed using a Scanning Electron Microscope. Microclimate parameters, including temperature and humidity at different floral structures, were recorded using a thermo-hygrometer and a lux meter. Pollinator activity was monitored hourly from 08:00 to 16:00 throughout anthesis. The highest light intensity and temperature were recorded between 11:00 and 13:00, with the perigone exhibiting the highest temperature.

Key results – The flower has brief blooming time only 5 days but the pollen can viable until 8 days. Four fly species from the families Sarcophagidae, Muscidae, and Calliphoridae were identified as primary pollinators, with Chrysomyia rufifacies being the most frequent visitor. The highest visitation occurred midday on days 1–2, followed by a decline on days 3–4. Pollinator visitation is influenced not only by biological traits and floral cues but is also significantly affected by environmental factors, particularly temperature and light intensity. Pollination is most likely to occur when female flowers bloom within one to seven days after male flowers, as pollen remains viable for up to eight days, allowing effective pollen transfer. However, the limited survival and lifespan of pollinators may contribute to the low reproductive success of this species.