Seed Swallowing in Tamarins

Source: P. A. Garber and U. Kitron, International Journal of Primatology, Volume 18, Number 4, 1997
Nonhuman primates represent a major component of the frugivore biomass in several rain-forest communities.
Although there is considerable evidence that prosimians, monkeys, and apes serve as dispersal agents for many tropical trees,
little attention has been paid to the more basic questions of why certain species of primates swallow and void seeds, and what, if any, are the advantages to an animal of having a large, hard, bolus pass through its digestive tract. We examine patterns of fruit-eating and seed-swallowing in two species of free-ranging tamarins: Saguinus mystax and Saguinus geoffroyi. Fruits commonly eaten by tamarins contain large seeds surrounded by a fibrous and adhesive pulp or arilate seed coat. They generally swallow seeds and pulp together. Intact seeds are voided over a 1- to 3-h period. Measurements of 132 seeds naturally voided by Panamanian tamarins average 11.2 mm in length and 0.3 g. The greatest number of large seeds contained in the digestive tract of a single animal at one time was 13. In the case of moustached tamarins, we collected 220 seeds. Average seed length is 11.9 mm and average seed weight is 0.3 g. At the time of capture, one animal had 26 seeds in its digestive tract. In both tamarin species, there is evidence of sex-based differences in feeding behavior. Adult female moustached and Panamanian tamarins swallowed and voided seeds of larger size than adult males did. Seed size is positively correlated with pulp weight (p <. 001), therefore females were selecting food items with higher nutritional rewards than adult males did. Given their small body size and relatively short digestive tract, why do tamarins swallow such large seeds? Although several explanations are possible, we propose that the large number and size of undigested seeds continuously passing through the tamarin gut serve a curative role in mechanically dislodging and expelling intestinal parasites—Ancanthocephala (spiny-headed worms)—from their digestive tracts.
Journal of Primatology