The Possible Roles of Ethanol in the Relationship Between Plants and Frugivores: First Experiments with Egyptian Fruit Bats

Abstract

In this paper we discuss how yeast, fungi ubiquitously present in sugar-rich fruit, can influence the interaction between frugivores and fleshy-fruited plants via ethanol. We suggest that plants, the seeds of which are mostly dispersed by vertebrates, exploit the ethanol from alcoholic fermentation by yeast in their seed dispersal strategy. Moderate consumption of ethanol, i.e., at concentrations close to those in naturally ripening fruit, by frugivores may have beneficial short- and long-term effects for these potential dispersers, whereas consumption of larger quantities may have negative short- and long-term effects. Ethanol vapor emanating from palatable fruit may act as an odor cue, guiding bats and other frugivores to the fruit, and aiding them to assess its quality. In addition, we suggest that ingested ethanol may be an appetitive stimulant. We also evaluate the possibility that ethanol within fruit may be used as a source of energy by frugivorous vertebrates. Our preliminary data indicate that Egyptian fruit bats (Rousettus aegyptiacus) can use the odor of ethanol to assess food suitability, but also that it may not serve as an attractant over short distances (i.e., <1 m). Instead, ethanol is avoided at concentrations greater than 1%, a value which might typically characterize overripe and otherwise unpalatable fruit. Our initial results further indicate that Egyptian fruit bats significantly decrease their food consumption if it contains 1 or 2% ethanol. Overall, ethanol may play diverse roles in the nutritional ecology and behavior of fruit-eating bats, and in the interaction between frugivores and plants, in general.

The Use of Commercial Fruits as Attraction Agents May Increase the Seed Dispersal by Bats to Degraded Areas in Southern Mexico

“…The attractiveness of these fruits for frugivorous bats most likely is due to the concentrations of ethanol, a final degradation product of the sugar present in all fruits, which exists in mature fruit and serves as an olfactory signal for these species (e.g. mango juice) [43].…”

Sugars are complementary resources to ethanol in foods consumed by Egyptian fruit bats

“…; after 130·min, 2.495( ϫ10 6 )±918123]. Even though there is little information in the literature on the ethanol content of fruits consumed by birds and bats, at least in Israel, it seems that birds and bats consume fruits that have a similar [EtOH] (Sánchez et al, 2004). So, there does not appear to be an a priori reason to expect that frugivorous birds should metabolize ethanol more efficiently than frugivorous bats.…”

“…Ethanol occurs ubiquitously in fleshy fruit as a by-product of the alcoholic fermentation of sugars mainly by micro-organisms, but also by the fruit itself (Battcock and AzamAli, 1998;van Waarde, 1991). Ethanol content increases as fruit ripens (Dominy, 2004;Dudley, 2004;Sánchez et al, 2004), suggesting that obligate frugivores, such as fruit bats, may consume significant amounts of this alcohol. For example, ripe fruit eaten by Egyptian fruit bats (Rousettus aegyptiacus, E. Geoffroy 1810) may contain ~0.1 to 0.7% ethanol, whereas unripe and overripe fruit may contain lower and higher concentrations, respectively (Sánchez et al, 2004).…”

“…Ethanol content increases as fruit ripens (Dominy, 2004;Dudley, 2004;Sánchez et al, 2004), suggesting that obligate frugivores, such as fruit bats, may consume significant amounts of this alcohol. For example, ripe fruit eaten by Egyptian fruit bats (Rousettus aegyptiacus, E. Geoffroy 1810) may contain ~0.1 to 0.7% ethanol, whereas unripe and overripe fruit may contain lower and higher concentrations, respectively (Sánchez et al, 2004). Our research on the effects of the presence of ethanol in artificial food on the foraging behaviour of captive Egyptian fruit bats indicated that at low concentrations (<1%) ethanol does not affect food selection, whereas at high concentrations (у1%) ethanol deters the bats (Sánchez et al, 2004;Sánchez et al, 2006).…”

“…For example, ripe fruit eaten by Egyptian fruit bats (Rousettus aegyptiacus, E. Geoffroy 1810) may contain ~0.1 to 0.7% ethanol, whereas unripe and overripe fruit may contain lower and higher concentrations, respectively (Sánchez et al, 2004). Our research on the effects of the presence of ethanol in artificial food on the foraging behaviour of captive Egyptian fruit bats indicated that at low concentrations (<1%) ethanol does not affect food selection, whereas at high concentrations (у1%) ethanol deters the bats (Sánchez et al, 2004;Sánchez et al, 2006). In addition, the ingestion of artificial food containing 1% ethanol can impair the flight skills of the bats (F.S., unpublished observations), i.e.…”