Nutritional and Digestive Challenges to Being a Gum-Feeding Primate

Abstract

Gum is an unusual food that presents significant challenges to animals that feed on it. Gum is limited in availability; trees generally secrete it only in response to damage. Gum is a β-linked complex polysaccharide, and as such is resistant to mammalian digestive enzymes and requires fermentation by gut microbes. It contains little or no lipid, low amounts of protein, and no appreciable levels of vitamins. As a food, gum can be characterized as difficult to obtain, potentially limited in quantity, difficult to digest, and primarily a source of energy and minerals. Despite these drawbacks, many primates feed extensively on gums. Among mammals, gum-feeding largely appears to be a primate dietary adaptation. Why are there so many primate gum-feeders and what adaptations have allowed them to make a living on such a problematic food? This is the central question of this book. This chapter examines digestive and nutritional aspects of gum. Specific examples of biological adaptations found in common and pygmy marmosets (Callithrix jacchus and Cebuella pygmaea), small New World primate gum-feeding specialists, will be examined. These marmoset species have many similarities in their behavior, morphology and metabolism, but also some instructive differences in their digestive function. C. pygmaea is the smallest of the marmosets but has the slowest passage rate of digesta. This might represent an adaptation to retain difficult-to-digest material, such as gum, within the gut to allow fermentation. In contrast, C. jacchus has a rapid passage rate. Passage rate in C. jacchus appears adapted more for rapidly excreting indigestible material (e.g., seeds) than for retaining gum within the gut to enable more complete digestion. Fruit is a rare component of C. pygmaea’s diet; hence any constraint on feeding caused by filling the gut with ingested seeds is greatly relaxed, apparently enabling digestive kinetics that favor digestive efficiency over maximizing food intake. Interestingly, however, these marmosets share an ability to digest gum despite their differences in gum kinetics. In captivity both species have been shown to be more able to digest Acacia gum than related species that feed less often on gum in the wild.