Supplementary material from "Urinary concentrations of a direct ethanol metabolite indicate substantial ingestion of fermenting fruit by chimpanzees"

Frugivorous animals routinely ingest fruit sugars and the associated products of microbial fermentation. Yeast-derived ethanol within fruit is a recently described chronic feature (~14 g/day) of the chimpanzee diet, but physiological evidence of exposure has not yet been demonstrated. We assayed urine collected from 19 wild chimpanzees for the presence of ethyl glucuronide (EtG), a direct metabolite of ethanol. Urine samples were obtained from study individuals feeding almost exclusively in the canopy of mast-fruiting Gambeya albida (=Chrysophyllum albidum), freshly fallen fruits of which averaged a pulp-ethanol content of 0.09% (±0.01 SE; range 0.01-0.40%) across multiple ripe crops. Of twenty individual urine samples (nine from females and eleven from males, aged 10-46 years), seventeen tested positive for EtG at an analytical threshold of 300 ng/mL; out of a subset of eleven of these positive samples, ten samples further tested positive at a threshold of 500 ng/mL. These values are high relative to calibrations of the test method for modern humans, and are consistent with substantial rates of ethanol consumption via frugivory in the wild.