Meeting Abstract
Fruit represents a substantial portion of many animal diets, especially in primates; chimpanzees routinely consume in excess of 10% of their body mass in fruit per day. As fruit ripens, the saccharide-rich contents are exposed to ecologically ubiquitous yeasts, which fermentatively produce ethanol. Yeast-derived ethanol can deter bacterial competitors within the internal fruit environment, may facilitate fruit localization and thus seed dispersal via animal olfactory responses, and may also stimulate appetite via psychoactive effects. Naturally occurring ethanol concentrations in fruit are, however, largely unstudied. During field studies at Ngogo, Kibale National Park, Uganda, we measured ethanol concentrations in the pulp of 23 species of fruit, 22 of which are known to be consumed by chimpanzees. All fruit tested had detectable levels of alcohols, ranging from 0.03% to 3.6%; the fruit species in our study represent approximately 50% of the chimpanzee diet at Ngogo, and these results are consistent with chronic low-level dietary exposure in this species. The higher elevation of Ngogo (1400 m) also suggests, via the Q10 effect (wherein enzymatic rates of yeast are cut in half with a 10-degree C drop in average temperatures), that ethanol levels in primate-consumed fruit at lower elevations may be substantially higher. These data are consistent with prolonged evolutionary exposure of all hominoid taxa, including ourselves, to dietary ethanol.
