Breeding systems of Bromeliaceae species: evolution of selfing in the context of sympatric occurrence

Co-occurring congener plant species in the highly diverse Atlantic forests of southeastern Brazil may act as natural laboratories for evaluating evolution of reproductive shifts. We assessed the breeding systems in a sympatric assemblage of bromeliad species and compiled literature available for the family to compare our experiments with available information. We performed controlled experiments of autonomous selfing, self- and cross-pollination in 40 species of 11 genera of two subfamilies that, in general, overlap their blooming period and share the same pollination vectors. We also tested for differences between self-compatible (SC) and self-incompatible (SI) species with regard to ecological factors such as abundance, co-flowering and co-occurrence. Most species experimentally tested and surveyed in the literature (75%) were SC. Species from the subfamily Tillandsioideae were predominantly SC, while Bromelioideae showed greater variation in breeding systems. About 43% of the species studied set fruits spontaneously in the absence of pollinator vectors. We found that SC species were the more abundant, were more frequently associated with other relatives and overlapped their blooming period with other species more than SI species. Thus, our results suggest that self-compatibility is common for Bromeliaceae and do not support the traditional hypothesis of reproductive assurance used to explain the evolution of selfing. We discuss self-compatibility as a reproductive isolating mechanism in the presence of pollen flow among sympatric congener species.