Taste preference threshold
White-faced sakis regularly consume unripe fruits, which means that their expected response would be to display a lower sensitivity to acidic tastants. However, this was not the case…
The taste preference threshold values of the white-faced sakis were within the range of those found in other primates.
Table 1. Taste preference thresholds of various primate species to five food-associated acids (mM).
Compared to other species, the most responsive individual of the white-faced sakis tested displayed similar taste preference thresholds to other ripe-fruit specialist primate species (such as the spider monkey). However, the least responsive individual displayed similar taste preference thresholds to the southern pig-tailed macaque, who have been reported to include unripe figs in their diet.
Despite their regular consumption of unripe fruits, white-faced sakis are not necessarily less sensitive to sour-tastes compared to other primates. This is likely due to the perception of acids being important for fruit selection, as not all fruits will be suitable for consumption at all stages of maturity.
Sour-taste tolerance
White-faced sakis display a relatively high tolerance for citric acid compared to other primates tested.
Table 2. Sour-taste tolerance in five species of non-human primates to citric acid concentrations of 10, 30 and 50 mM (mM), respectively. The values reported in the table correspond to the concentration of sucrose required by each species to prefer a mixture of a given concentration of citric acid (10, 30 or 50 mM) and sucrose over a solution of 50 mM sucrose.
White-faced sakis display sour-taste tolerance thresholds most similar to that of the southern pig-tailed macaque. This would be expected, as this species is also known to consume unripe fruits
The high sour-taste tolerance of white-faced sakis is likely attributed to their diet consisting of a large proportion of unripe fruits.
The consumption of unripe fruits provides the white-faced sakis with an advantage over other sympatric frugivorous primates. Unripe fruits often have a longer period of availability, and are not exploited by as many species as ripe fruits are. This also allows white-faced sakis to avoid seasonal bottlenecks in ripe fruit availability that affect ripe fruit specialists.
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