The Chemical Ecology of Lemur Seed Dispersal

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Many tropical angiosperms rely on frugivores for seed dispersal and evolved fleshy fruits to attract them. While it is still arguable to what extent fruit characteristics are malleable to selection pressures exerted by their main seed-dispersal vectors, several studies have demonstrated that traits such as fruit color, scent or size may have evolved in response to frugivore feeding behavior. Consequently, it has been shown that fruit odor in bat-dispersed figs may be an adaptation whose function is to attract frugivorous bats and promote seed dispersal. Primates constitute a significant share of the community of frugivores in many tropical systems and are important seed dispersers of many plant species. In recent years, it has become increasingly clear that they possess high olfactory capacities which are especially useful in the fruit selection phase. Thus, it is possible that fruits whose main dispersal vector is primates have evolved to signal their ripeness through olfactory cues, i.e. fruit odor. This hypothesis has received preliminary support in a recently completed DFG-funded project, which found that among four Neotropical fleshy fruit species, only primate-dispersed species emit strong, compound-rich and unique odors at ripeness and that these odors allow spider monkeys to discriminate between ripe and unripe fruits. The proposed project will build upon these preliminary results and attempt to establish the hypothesis that fruit odor is an adaptation to primate seed dispersal, i.e. that it has evolved to mediate the communication between angiosperms and primate which disperse their seeds. The project will take place in Madagascar, a biodiversity hotspot in which lemurs, the local primates, are the main vertebrate seed-dispersal vector. Lemurs possess lower color discrimination abilities than most other Paleotropical primates and are presumed to strongly rely on olfaction, thus making them an ideal model system to test the hypothesis. The project will ask four major questions: (Q1) Does fruit odor mediate the communication between lemurs and plants whose seeds they disperse? (Q2) Is there evidence that fruit odor has evolved to fulfill this function? (Q3) What information regarding fruit quality can lemurs infer from their odor? (Q4) Is there evidence that the lemur olfactory system has evolved in response to the odors of fruits? To answer these questions, this interdisciplinary project will apply methods from chemical ecology, behavioral ecology, botany, genetics and microbiology, in collaboration with experts in all of these fields. Taken together, answering these questions may begin establishing whether and how lemurs and plants have gone through a chemical coevolution in which fruit odor and lemur olfaction coevolved to mediate the mutualistic interaction between them.