Floral biology, nectar secretion pattern and fruit set of a threatened Bignoniaceae tree from Brazilian tropical forest

Zeyheria tuberculosa, a Bignoniaceae tree that occurs in a broad latitudinal range in Brazilian forests, is a threatened species of seasonal tropical forest. It is crucial to enhance the knowledge on this species’ floral biology, since interactions related to reproduction of plants are critical for the long term maintenance of their populations. Thus, we investigated the sexual reproduction and floral biology of Z. tuberculosa, focusing on nectar features, aiming to understand the ecological processes associated to this mutualistic plant-animal interaction in the current modified landscape. For this, we performed experiments under natural conditions and laboratory. All the evaluated plants were self-incompatible. Zeyheria tuberculosa was pollinated by Bombus pauloensis, a medium-sized bee, and offered hexose-rich nectar as resource. Flowers were also visited by small-sized bee species, Trigona spinipes, that acted as pollen thief, and Pseudoaugochlora pandora and P. graminae that acted as nectar thieves. These three bee groups exhibited temporal separation in the peak of visits throughout the day. The peak of pollinator visits occurred firstly, which may allow the pollinator to access nectar and pollen loads before they are exploited by thieves. However, bee pollinator visits were scarce, and this fact, associated to the self-incompatibility of Z. tuberculosa, may explain the low fruit set registered in the studied plants. It could be of special concern for this threatened species maintenance in the medium and long term, which depends on the offspring originated by sexual reproduction.