Why feed on fungi? The nutritional content of sporocarps consumed by buffy-headed marmosets, Callithrix flaviceps (Primates: Callitrichidae), in southeastern Brazil.

The typical diet of Callithrix marmosets is based on gums, although fungi are the dietary staple of a single group of Callithrix flaviceps studied in the Augusto Ruschi Biological Reserve, in southeastern Brazil. Here, we present the nutritional composition of two species of Mycocitrus fungi consumed by C. flaviceps, and discuss possible determinants of the preference of the marmosets for fungi over gums. The fungi were high in sugar/fiber and poor in proteins, and were similar in composition to the gums exploited by other marmosets and to the fungi consumed by Callimico goeldii. The reduced protein content of the fungi may be offset by the arthropod component of the diet of the Callithrix flaviceps study group. The low relative metabolic rate and enlarged cecum of Callithrix enable these marmosets to exploit foods with a high fiber content. In addition, the greater digestibility of chitin in comparison with plant fiber may make fungi a nutritionally more valuable resource to marmosets than gums. Marmosets, thus, may prefer to feed on fungi when an adequate supply of this resource is available in the environment.