Taste responsiveness of Western chimpanzees (Pan troglodytes verus) to five food-associated saccharides

Abstract

Using a two-bottle choice test of short duration, we determined taste preference thresholds for sucrose, fructose, glucose, lactose, and maltose in three Western chimpanzees (Pan troglodytes verus). Further, we assessed relative preferences for these five saccharides when presented at equimolar concentrations and determined taste preference difference thresholds for sucrose, that is, the smallest concentration difference at which the chimpanzees display a preference for one of the two options. We found that the chimpanzees significantly preferred concentrations as low as 20 mM sucrose, 40 mM fructose, and 80 mM glucose, lactose, and maltose over tap water. When given a choice between all binary combinations of these five saccharides presented at equimolar concentrations of 100, 200, and 400 mM, respectively, the animals displayed significant preferences for individual saccharides in the following order: sucrose > fructose > glucose = maltose = lactose. The taste difference threshold for sucrose, expressed as Weber ratio (ΔI/I), was 0.3 and 0.4, respectively, at reference concentrations of 100 and 200 mM. The taste sensitivity of the chimpanzees to the five saccharides falls into the same range found in other primate species. Remarkably, their taste preference thresholds are similar, and with two saccharides even identical, to human taste detection thresholds. The pattern of relative taste preferences displayed by the chimpanzees was similar to that found in platyrrhine primates and to the pattern of relative sweetness as reported by humans. Taken together, the results of the present study are in line with the notion that taste sensitivity for food-associated carbohydrates may correlate positively with phylogenetic relatedness. Further, they support the notion that relative preferences for food-associated carbohydrates, but not taste difference thresholds, may correlate with dietary specialization in primates.

Is sugar as sweet to the palate as seeds are appetizing to the belly? Taste responsiveness to five food-associated carbohydrates in zoo-housed white-faced sakis, Pithecia pithecia

“…The relative taste preferences found in the present study can therefore be considered as an approximation of the relative sweetness of the five saccharides as perceived by the whitefaced sakis. The pattern of relative taste preference displayed by the sakis (sucrose > fructose > glucose � maltose = lactose) is identical or at least very similar to that found in previous studies with spider monkeys [56], squirrel monkeys [55], black-and-white ruffed lemurs [28], and chimpanzees [25] (Table 2). It is also similar to the pattern of relative sweetness as perceived by human subjects [57].…”

“…Chimpanzees ( Pan troglodytes ), for example, are considered as seed-dispersing ripe-fruit specialists [ 32 ] but nevertheless display higher taste preference threshold values, and thus a lower sensitivity, with all five saccharides than the white-faced sakis of the present study [ 25 ]. Similarly, black-and-white ruffed lemurs ( Varecia variegata ) are less sensitive for all five carbohydrates compared to Pithecia pithecia [ 28 ], despite being highly frugivorous seed-dispersers [ 33 ].…”

“…For each animal, the amount of liquid consumed from each bottle was recorded, summed for the 10 test trials with a given stimulus combination, converted to percentages (relative to the total amount of liquid consumed from both bottles), and 66.7% (i.e., 2/3 of the total amount of liquid consumed) was taken as criterion of preference. This rather conservative criterion was adopted for purposes of comparability with previous studies using the same criterion in other primate species [9,25,[27][28][29][30][31] and in order to avoid misinterpretation of data due to a too liberal criterion.…”

“…Additionally, we assessed relative taste preferences in white-faced sakis for the five carbohydrates mentioned above. Previous studies have found that nonhuman primates also differ in the pattern of relative taste preferences and thus in their perception of the relative sweetness and, concomitantly, of the sweetening potency of naturally occurring soluble carbohydrates, possibly due to differences in their dietary habits [ 25 ].…”

Taste detection threshold of human (Homo sapiens) subjects and taste preference threshold of black-handed spider monkeys (Ateles geoffroyi) for the sugar substitute isomalt

“…For each animal, we recorded the amount of liquid consumed from each bottle, summed it for the ten trials with a given stimulus combination, converted it to a percentage (relative to the total amount of liquid consumed from both bottles), and took 66.7% (i.e., 2/3 of the total amount of liquid consumed) as the criterion of preference. We chose this rather conservative criterion for reasons of comparability of data, as the same criterion had been used in previous studies on sweet-taste responsiveness with both spider monkeys (Laska et al 1996 , 1998 , 1999a , 2001 ) and other primate species (Laska et al 1999b ; Laska 2000 ; Wielbass et al 2015 ; Nicklasson et al 2018 ; Norlén et al 2019 ), and in order to avoid misinterpretation due to a too liberal criterion. Additionally, we performed binomial tests and regarded an animal as significantly preferring one of the two stimuli if it reached the criterion of 66.7% and consumed more from the bottle containing the preferred stimulus in at least eight out of ten trials (binomial test, p < 0.05).…”