Aliphatic esters: The missing link in fruit-frugivore olfactory communication?

• Applicant: Dr. Omer Nevo
• Subject Area: Ecology and Biodiversity of Animals and Ecosystems, Organismic Interactions ; Organismic Interactions, Chemical Ecology and Microbiomes of Plant Systems
• Term: from 2017 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 397399570

Fruit odor has only recently been recognized as an important source of information to frugivores and potentially as a signaling system mediating the mutualistic interaction between plants and seed-dispersers. Most studies on fruit odor have focused on entire odor bouquets of ripe fruits and did not consider the roles of individual chemicals in conveying information to frugivores. An exception to this are ethanol and methanol, which are both byproducts of fruit maturation due to sugar fermentation or cell-wall degradation and have been suggested to be used by animals. Yet behavioral tests failed to document their function as attractants of frugivores. This may be the results of their deleterious effects. Aliphatic esters are ubiquitous in fruit odor and are responsible for most of what people perceive as fruity odor. They are often synthesized by flowers to increase their odor profiles and attract pollinators. Crucially, they are a direct biochemical product of alcohols such as methanol and ethanol. Many fruits actively synthesize aliphatic esters upon ripeness and alcohols are in fact a limiting factor in ester production. As a result, aliphatic esters in fruit odor are likely to be highly correlated with methanol and ethanol level and thus with fruit ripeness. The project will test the hypothesis that (a) fruit maturation is accompanied with increased levels of methanol and ethanol; (b) these alcohols are converted to aliphatic esters which are emitted as fruit odor, thus making ester levels in the odor an honest signal for fruit ripeness; and (c) that animals feeding on these fruits and dispersing their seeds are attracted to aliphatic esters and use them for fruit selection. The project will be conducted in Kibale National Park and Nagugabo Research Station, Uganda. It will incorporate chemical analysis of wild fruits and behavioral experiments with monkeys and, for the first time, wild African elephants. The results are expected to provide a high-resolution outlook on the evolutionary ecology of fruit odor and particularly aliphatic esters, as well as to develop methods which can be applied in many future studies in the field.

• DFG Programme: Research Grants