Gustatory responsiveness to food-associated acids in the spider monkey (Ateles geoffroyi)

The gustatory responsiveness of four adult spider monkeys to five food-asso ciated acids was assessed in two-bottle preference tests of brief duration (3 min). The animals were given the choice between a 30 mM sucrose solution and defined concentrations of citric acid, ascorbic acid, malic acid, acet ic acid, or tannic acid dissolved in a 30 mM sucrose solution. With this pr ocedure, Ateles geoffroyi was found to significantly discriminate concentra tions as low as 5 mM ascorbic acid, citric acid, and acetic acid, 10 mM mal ic acid, and 0.1 mM tannic acid from the alternative stimulus. With the lat ter two substances, the monkeys rejected all suprathreshold concentrations tested, whereas with the former three substances, the animals showed an inv erted U-shaped function of preference, i.e. they rejected high concentratio ns, but significantly preferred low but detectable concentrations of these acidic tastants over the alternative sweet stimulus. The results showed (1) the spider monkey to respond to the same range of acid concentrations as o ther nonhuman primate species; (2) that Ateles geoffroyi is able to detect food-associated acids at concentrations well below those present in most fr uits; and (3) that unlike most other primate species tested so far, spider monkeys do not generally reject acidic tastants but show a substance- and c oncentration-dependent change in responsiveness that may range from rejecti on to preference. The results support the assumptions that spider monkeys m ay use sourness and/or astringency of food-associated acids as a criterion for food selection, and that the gustatory responsiveness of Ateles geoffro yi to acidic tastants might reflect an evolutionary adaptation to frugivory .