Feeding habits of marmosets: A case study of bark anatomy and chemical composition of Anadenanthera peregrina gum

Primates of the genus Callithrix often obtain exudates from plants of the family Fabaceae. This study characterizes the chemical composition of exudates, and the anatomy and hystochemistry of the secretory ducts in the bark of Anadenanthera peregrina (L.) Speg. var. peregrina (Fabaceae). Exudates from this tree species represent an important component of the diet of hybrid marmosets, Callithrix spp. (Primates: Cebidae). A. peregrina was selected as the focal study tree because it is the only gum tree species exploited by Callithrix groups present within five urban forest fragments in the municipality of Viçosa, Minas Gerais State, Brazil. Gum samples were obtained directly from gouges made by the marmosets, while bark samples were obtained from A. peregrina plants, whether or not they were damaged by the marmosets. Constitutive secretory ducts were present in the bark of ungouged A. peregrina, whereas, marmoset damage caused induced secretory duct formation and an increase in the size of these ducts. The gum produced in the gouges made by the marmosets and in ungouged plants reacted positively to tests for polysaccharides, pectin, mucilage, and proteins. The gum from the gouges exhibited high water (41.0%), carbohydrate (38.2%), protein (19.0%), and mineral (Ca 0.4% and K 0.3%) content. We argue that the relatively high calcium content of A. peregrina gum plays an important nutritional role in, balancing a diet that is otherwise rich in phosphorous and poor in calcium.