Condensed tannins in the diets of primates: a matter of methods?

Abstract

To understand the ways in which condensed tannins (CT) affect primate diet selection and nutritional status, correct measurements are essential. In the majority of studies of the CT contents of primate foods, a tannin source such as "quebracho" is used to standardize CT assays, but the CT in quebracho tannin may not be similar to those in the plants of interest. We investigated how the choice of standard to calibrate CT assays affects the estimation of CT in the diets of mountain gorillas (Gorilla beringei). We purified the CT from gorilla foods and compared the actual amounts of CT in the foods with estimates produced by using the quebracho tannin. When quebracho was used, the estimates of CT contents of gorilla foods were, on average, 3.6 times the actual content of CT so that the amounts in frequently eaten gorilla foods were substantially overestimated. The overestimation for a given plant could not be predicted reliably and the ranking of plants by tannin content differed according to the standard used. Our results demonstrate that accurate measurements of CT necessitate the use of tannins purified from the plant species of interest. A reevaluation of primatology studies using interspecific comparisons of tannin content will provide new insights into primate food selection and nutritional ecology.

Nutrient and plant secondary compound composition and iron‐binding capacity in leaves and green stems of commonly used plant browse (Carolina willow; Salix caroliniana) fed to zoo‐managed browsing herbivores

“…We used a standard curve created with purified willow condensed tannin to obtain an absolute dry weight concentration. Consequently, our results may not be exactly comparable to concentrations reported for tannins in previously reported trials [Rothman et al, 2009]. Results reported in reference to a standard can be problematic because reactivity is variable depending on (1) the standard chosen and (2) the chemical profiles of the different species/cultivars tested.…”

Nutritional geometry: gorillas prioritize non-protein energy while consuming surplus protein

“…Leaves form the majority of the diet for most of the year since fruits are seasonally unavailable [17], suggesting that this gorilla population is physiologically adapted to eating and excreting excess nitrogen. Tannins, which may contribute 4 per cent of the diet on a dry matter basis, might reduce protein availability [23], but some staple leaves do not have tannins, yet many of the commonly eaten fruits do [8]. For those leaves that contain high-tannin levels, their protein-precipitating capacity might aid gorillas to void Nutritional rails indicate AP to NPE balance in fruit and leaf periods (derived from data in (a), weighted by successive two-month intervals over 1 year [17]), the balance of AP to NPE in mid-lactation gorilla milk [20], and the recommended balance of AP to NPE for humans to maintain healthy diets [21].…”

Niche Partitioning in Sympatric Gorilla and Pan from Cameroon: Implications for Life History Strategies and for Reconstructing the Evolution of Hominin Life History

“…As a case in point, Rothman and colleagues [81] argued that the amount of protein eaten by mountain gorillas exceeds their daily requirements even after protein intake was corrected for the effects of condensed tannins [82] and the fiber-bound unavailable N [83], [84]; the high-protein diet and its consistent availability underlies the high growth rates observed in mountain gorillas [19]. Western lowland gorillas, too, avoid foods rich in tannins and lignin [39], which could potentially offset their greater consumption of protein-rich vegetative matter.…”