WAS THE EVOLUTION OF ANGIOSPERM-FRUGIVORE INTERACTIONS DRIVEN BY RECIPROCAL COEVOLUTION BETWEEN THEM?

Abstract

The evolution of fruits contributed to the dominance of angiosperms and provided new ecological opportunities for frugivore vertebrates to diversify. However, it is not yet clear whether reciprocal coevolution between plants and frugivores drove the evolution of their mutualistic interactions. This review aimed at discussing major events of the evolution of fleshy-fruited angiosperms and their major seed dispersers, in order to elucidate if and how they responded to mutual selective pressures. Angiosperms evolved between the Mid and Late Cretaceous and they experienced a large diversification until the early Eocene. However, all main lineages of extant frugivores originated from the Eocene onward: frugivorous birds evolved in the Eocene but diversified in the Oligocene; primates evolved in the early Eocene and frugivorous bats diversified in the Oligocene-Miocene. This divergence in the times of the origins of angiosperm and their modern seed dispersers suggest that other animals interacted with early angiosperms. The most likely candidates are the rodent-like multituberculates. Several studies investigated how plant-frugivore mutualistic interactions contribute to the diversification in both plants and animals and we draw two main hypotheses from them: the plant-frugivore coevolutionary hypothesis and the neutral hypothesis. There are consistent evidences supporting each of these hypotheses, which suggest that they may not be mutually exclusives. An integrative approach is that plant-frugivore coevolution happens in pulses. Times of high environmental disturbances promote significant changes in mutualistic interactions and release new ecological opportunities for emerging species, which in turn exert stronger selective pressures and adaptive changes on fruit and frugivores traits. As evolving frugivores occupies those niches, interactions become more stable and coevolution is weaker and diffuse. We are currently undergoing a new period of unstable plant-frugivore interactions and we need more information on plant-frugivore coevolution in order to predict how species will respond to a changing world.