The Chemical Ecology of Primate Seed Dispersal

Abstract

Many tropical angiosperms rely on frugivores for seed dispersal and evolved fleshy fruits to attract them. Although both sides of the interaction are generalists, frugivores do not feed on the full range of fruit species in their habitats and angiosperms rely on the dispersal services of only a share of the frugivore community. This observation led to the "Dispersal Syndrome Hypothesis", which postulates that over time fruits evolve to specialize on certain guilds of frugivorous seed dispersers and consequently their traits evolve in response to the dietary and sensory capacities of their main dispersal agents.Fruit traits such as size, seed size and husk thickness have been shown to be malleable to selection pressures exerted by their main seed-dispersal vectors. Additionally, due to competition for dispersal services and the need to promote consumption of ripe fruits and thus dispersal of mature seeds, fruits are also under selection pressures to provide reliable signals for ripeness. A prime example is fruit color, which has evolved independently in many bird-dispersed species to signal ripeness and possibly nutrient content. Fruit odor, similarly, has been speculated to be a signaling system between plants and frugivores with elaborated olfactory capabilities, but this has only recently received support in figs (genus Ficus) dispersed by bats. Yet data are still restricted to the narrow bat-fig model system and it is not clear whether fruit olfactory signaling has evolved in other plant genera and in the communication with other taxa, and thus indeed a recurring component of some Dispersal Syndromes.Primates are one of the most important seed dispersal vectors in the tropics. Until recently, their olfactory capabilities were considered low and thus irrelevant for the study of their feeding ecology.This view has been utterly revisited over the past years and primates are now known to possess high olfactory capacities. Therefore, under the framework of the Dispersal Syndrome Hypothesis, it is likely that fruits whose seeds they disperse evolved olfactory signals for ripeness, too. This thesis explores the evolution and functions of fruit aroma in the communication between primates and plants. The first chapter is a theoretical review regarding the roles of olfaction in primate feeding ecology. It concludes, based on available behavioral works, that frugivory is the