Floral diversification and reproductive strategies in species with pollen flowers: evolution of buzz pollination in Chamaecrista

Abstract

Mutualistic interactions involve reciprocal exploitation between species, in which both species benefits. In pollination, the interests of the plant and the pollinator are different, and a conflict is expected. For the plant, it is interesting that bees increase reproductive success on visits with maximum pollen transfer to the stigma. As for the bees, plants must provide the maximum floral resources in a few visits. However, there is a great morphological variation between flowers, determining floral attractiveness and the amount of pollinator reward. For example, variation in floral size is associated with changes in the number of pollen grains and ovules in flowers. The same occurs with herkogamy, in which species with small flowers have their reproductive organs closer together, which can increase the probability of self-fertilization. Floral trait variations are associated with different reproductive strategies ranging from obligatory self-pollination to obligatory cross-fertilization, determining a gradient of reproductive dependence of plant species on their pollinators. Although these patterns are described for different groups of angiosperms, plant lineages with pollen flowers, represented by about 8% of flowering plants, have not been properly investigated. These plants have flower with poricidal anthers that trap pollen grains, the only floral resource available, and may function differently from other angiosperms. In this doctoral project, we seek to explore this knowledge gap from an evolutionary perspective. In this case, the emergence and modification of complex structures such as pollen flowers may have been optimized by selection exerted by bees vibrating poricidal anthers and constrained by other evolutionary forces. In this context, it is expected that such structures evolve towards different phenotypic optima over time, depending on the biotic and abiotic context in which the diversification of these plants occurred. (AU)