Ethanol and Methanol as Possible Odor Cues for Egyptian Fruit Bats (Rousettus aegyptiacus)
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Frugivorous bats from the Old and New World use odor cues to locate and assess fruit condition. We hypothesized that Egyptian fruit bats (Rousettus aegyptiacus) use as odor cues those volatile compounds that increase in emission rate as fruit ripens. We examined whether the smell of fermentation products may indicate the degree of ripeness to fruit bats. We analyzed volatile compounds in the headspace (the gas space above a fruit in a closed container) of dates (Phoenix dactylifera) and rusty figs (Ficus rubiginosa), both of which are consumed by fruit bats, to elucidate which compounds originate from fermentative pathways and to determine which change in emission rate during ripening. Ethanol, acetaldehyde, and acetic acid were the only volatile compounds detected as products of fermentation in both fruits. In dates, emission rates of these compounds increased during maturation, whereas in rusty figs, they decreased or remained constant. Methanol, although not a fermentation product, increased in emission rate during ripening in both fruits. We found that R. aegyptiacus was neither attracted nor deterred by the smell of methanol at any of the concentrations used. Although the odor of ethanol emanating from food containing concentrations similar to those found in ripe fruit did not attract the bats, at relatively high concentrations (≥1%), the smell of ethanol deterred them. Thus, ethanol at high concentrations may serve as a signal for bats to avoid overripe, unpalatable fruit.
KeywordsEthanol Fermentation Ficus rubiginosa Food selection Fruit-eating bats Methanol Odorcues Olfaction Phoenix dactylifera Rousettus aegyptiacus Volatile compounds
We thank A. Zabari, A. Fennec, and R. Glukhikh for their help capturing and maintaining the bats and to Prigat International Ltd. for contributing mango juice. We also thank two anonymous reviewers for constructive comments. Support by US–Israel Binational Science Foundation grant number 2001038 to C.K., B.P., and R.D., a stipend and a student research grant from the Mitrani Department of Desert Ecology (MDDE) to F.S., and a grant from the European Community, Access to Research Infrastructure–Improving Human Potential Programme to F.S. are gratefully acknowledged. This is paper number 571 of the MDDE.
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