Pollination biology of melittophilous legume tree species in the Atlantic Forest in Southeast Brazil

Abstract

This study describes the floral phenology and morphology, reproductive biology and pollinators for eight legume tree species, Schizolobium parahyba, Senna macranthera, and Senna multijuga (Caesalpinioideae), as well as Andira fraxinifolia, Lonchocarpus cultratus, Pterocarpus violaceus, Swartzia oblata, and S. simplex (Papilionoideae), in the Atlantic Forest in Southeast Brazil. All the studied species showed an annual flowering pattern, and almost all are of the cornucopia-flowering type, with the only exception being Swartzia oblata, which was of the steady-state type. In general, the legume flowers studied are conspicuous, mostly medium-sized, and offer nectar and/or pollen as a resource. Self-incompatibility associated with the production of many flowers and consequent pollen discounting due to self-pollination may contribute to low fruit set of these species in natural conditions. Fifty bee species were recorded visiting the flowers, with medium to large-sized Apidae bees, such as Bombus morio, and species of Xylocopa, Centridini and Euglossina, which were among the most frequent visitors and major pollinators. These bees showed high floral constancy, thus they are significant to the reproductive success of these tree species. This study provides information regarding the interactions between bees and these eight legume species and evaluates the importance of pollinators for their sexual reproduction.

Heteromorphic stamens are differentially attractive in Swartzia (Fabaceae)

“…Some aspects of the interaction between the flowers of S. flaemingii and S. simplex with the floral visitors seem to be recurrent in the other species of Swartzia ( Lopes and Machado 1996 ; Moço and Pinheiro 1999 ; Pinheiro et al 2018 ). One of them is that bees that collect pollen by vibrating the stamens always grab the smaller stamens.…”

“…Another aspect is that both types of stamens release their pollen grains during the same vibration event. However, the pollen deposition site differs in relation to the bee body ( Pinheiro et al 2018 ). The pollen released by the smaller stamens is preferentially deposited on the ventral region of the bee (sternotribic deposition).…”

“…The Swartzia species in general, despite very similar anthesis dynamics, present considerably different pollinator guilds ( Lopes and Machado 1996 ; Moço and Pinheiro 1999 ; Pinheiro et al 2018 ). The flowers of Swartzia flaemngii and S. simplex are visited by different groups of bees, such as carpenters, bumblebees, oil bees and stingless bees.…”

“…Images were captured with a Nikon DSLR D7200 Digital Camera. Pinheiro et al (2018) studied the floral visitors of both species (however, S. flaemingii was referred to as ‘ Swartzia oblata ’), while our observations were focused on the pollen collection behaviour and interaction of the animals with the floral parts. Visitors were grouped according to their pollen gathering behaviour following the terminology proposed by Portman et al (2019) .…”

“…The bees that pollinate Swartzia flowers are capable of vibrating the stamens ( Lopes and Machado 1996 ; Moço and Pinheiro 1999 ; Pinheiro et al 2018 ). The arrangement of the stamens in Swartzia and the behaviour of these bees for pollen collection suggest that the smaller stamens are associated with feeding the pollinator while the larger stamens are linked to the reproductive role of pollination.…”