Gustatory responsiveness to food-associated sugars and acids in pigtail macaques, Macaca nemestrina

Taste-preference thresholds for five food-associated sugars and acids, resp ectively as well as relative sweet-taste preferences were assessed in six p igtail macaques using two-bottle choice tests of brief duration (1 min). In experiment I, the animals were found to significantly prefer concentration s as low as 10 mM maltose and sucrose, 20 mM fructose and glucose, and 30 m M lactose over tap water. In experiment 2, the monkeys were given a choice between all binary combinations of the same five saccharides presented in e quimolar concentrations of 50, 100, 200, and 400 mM. Preferences for indivi dual sugars were stable across the concentrations tested and indicate the f ollowing order of relative effectiveness: maltose > sucrose> glucose greate r than or equal to fructose greater than or equal to lactose. In experiment 3, Macaca nemestrina was found to significantly discriminate concentration s as low as 5 mM malic acid, 10 mM ascorbic acid, 20 mM citric acid and ace tic acid, and 0.5 mM tannic acid from the alternative stimulus. With the la tter substance, the monkeys rejected all suprathreshold concentrations test ed, whereas with the former four substances, the animals showed an inverted U-shaped function of preference. The results showed pigtail macaques to be the first primate species tested so far whose taste-preference threshold for maltose is as low as that for s ucrose, and which - similar to rodents - prefers maltose over equimolar con centrations of sucrose and other saccharides. Further, unlike most other pr imates, pigtail macaques do not generally reject acidic tastants but show a substance- and concentration-dependent change in their behavioral response that may range from rejection to preference. The results support the assum ption that the gustatory responsiveness of M. nemestrina to food-associated sugars and acidic tastants might reflect an evolutionary adaptation to its dietary habits. (C) 2000 Elsevier Science Inc. All rights reserved.