Sour-Taste Tolerance in Four Species of Nonhuman Primates

Abstract

The taste of most fruits is characterized by a mixture of sensations termed sweet and sour by humans, and the food selection behavior of primates suggests that they may use the relative salience of sweetness and sourness to assess palatability of potential food items. Therefore, taste responses of six squirrel monkeys, five pigtail macaques, four olive baboons, and four spider monkeys to sweet-sour taste mixtures were assessed in two-bottle preference tests of brief duration (2 min). Monkeys were given the choice between a reference solution of 50 mM sucrose and mixtures containing 10, 30, or 50 mM citric acid plus 10, 20, 50, 100, 200, 400, 800, or 1000 mM sucrose. We found that the four species differed markedly in their acceptance of physiological concentrations of sour-tasting citric acid. Whereas olive baboons showed the highest degree of sour-taste tolerance and actually preferred most of the sweet-sour taste mixtures over sweet-tasting reference solutions, squirrel monkeys showed the lowest degree of sour-taste tolerance and rejected most of the sweet-sour taste mixtures even when they contained considerably more sucrose than the reference solutions. Additional tests demonstrated that the preference for sweet-sour taste mixtures was not based on masking effects. Rather, the animals perceived both the sweetness and the sourness of the taste mixtures and made a trade-off between the attractive and aversive properties of the two taste qualities. The results of this study suggest that the proximate reason for the marked differences in acceptance of sweet-sour taste mixtures are differences among species in the hedonic evaluation of the sour taste of citric acid. Possible ultimate reasons, which do not necessarily exclude, but may complement each other, include evolutionary adaptation to dietary specialization, avoidance of competition pressure, and phylogenetic relatedness.

Taste difference thresholds for monosodium glutamate and sodium chloride in pigtail macaques (Macaca nemestrina) and spider monkeys (Ateles geoffroyi)

“…2/3 of the total amount of liquid consumed) was taken as the criterion of preference. This criterion was chosen for reasons of comparability of data as the same criterion had been used in previous studies using the same method with the same or other primate species [Laska, 1994[Laska, , 1996[Laska, , 1997[Laska, , 1999[Laska, , 2000Laska & Hernandez Salazar, 2004;Laska et al, 1996Laska et al, , 1998Laska et al, , 1999aLaska et al, ,b, 2000bLaska et al, , 2001Laska et al, , 2003, and to avoid misinterpretation of data because of a too liberal criterion.…”

“…Animals of both species were housed as social groups in enclosures (10 Â 6 Â 4 m for the spider monkeys, and 6 Â 5 Â 3 m for the pigtail macaques) with adjacent single cages that could be closed by sliding doors to allow temporary separation of animals for individual testing (for details of maintenance, see Laska & Hernandez Salazar, 2004;Laska et al, 2003). Animals were fed commercial monkey chow, fresh fruit, and vegetables ad libitum.…”

“…All animals had served in previous studies using the same method [Laska & Hernandez Salazar, 2004;Laska et al, 2003], they were trained to enter the single cages voluntarily, and were completely accustomed to the procedure described below.…”

Howler Monkeys

“…Thus, no data on sensitivity in terms of taste detection thresholds for gustatory stimuli or on the ability to discriminate between different qualities or intensities of tastants are available. The taste function has been studied intensively in several nonhuman primates using a simple psychophysical method, the two-bottle preference test (e.g., Glaser 1979 ;Laska et al 2003Laska et al , 2009Laska and Hernández-Salazar 2004 ). This test assesses gustatory responsiveness to any tastant by giving an animal the option to choose between two bottles containing either tap water or a defi ned concentration of a tastant dissolved in tap water.…”

The evolution of sour taste

“…Breslin's hypothesis is germane to a number of primate species that forage in open habitats. It could account, for instance, for the evolution of sour taste preferences in olive baboons ( Papio anubis ; [69]). It is also germane to the story of the common ancestor of chimpanzees, gorillas and modern humans, a species that lived roughly 10 Ma, a story that we now consider in more detail.…”