Bat or bee pollination? Floral biology of two sympatric Cayaponia species (Cucurbitaceae) in Southeast Brazil

The evolution of pollination systems is unclear for many plant taxa due to the scarcity of field observations on floral visitors. Supposed bat- and bee-pollination is reported for species of the genus Cayaponia, but <5 % of these were observed in the field and their pollinators recorded. We studied the pollination biology of two early diverging sister species of Cayaponia, C. cabocla and C. pilosa, recording the floral biology, phenology, breeding system, floral visitors, and floral scent chemistry. Both species are monoecious and have bell-shaped white to greenish flowers. The length of the C. cabocla flowers was 2.33 ± 0.52 cm and of the C. pilosa flowers it was 2.75±0.95 cm. In C. cabocla nectar volume of male flowers was 180±57.15 μl and sugar concentration was 28.75±0.95%, whereas in female flowers the average volume was 46.5 ± 10.24 μl and sugar concentration was 22.5 ± 0.57%. Cayaponia cabocla flowers opened at late night, around 03:30 h, whereas those of C. pilosa opened around noon. Both species bloom in the austral summer (January-February) and depend on bees to set fruit, in addition to having a few floral visitor species in common. Whereas some of the flower traits resemble those of bat-pollinated plants (most notably the large nectar volume and nocturnal anthesis), the floral volatiles of both C. cabocla and C. pilosa are typical of flowers pollinated by bees. This study clarifies the pollination system of two Cayaponia species and provides new information that can be used to reconstruct pollination system transitions in this rich genus of cucurbits.