SEED SWALLOWING IN TAMARINS - EVIDENCE OF A CURATIVE FUNCTION OR ENHANCED FORAGING EFFICIENCY

Nonhuman primates represent a major component of the frugivore biomass in several rain-forest communities. Although there is considerable ev idence that prosimians, monkeys, and apes serve as dispersal agents fo r many tropical trees, little attention has been paid to the more basi c 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 f ruit-eating and seed-swallowing in two species of free-ranging tamarin s: Saguinus mystax and Saguinus geoffroyi. Fruits commonly eaten by ta marins contain large seeds surrounded by a fibrous and adhesive pulp o r arilate seed coat. They generally swallow seeds and pulp together. I ntact seeds are voided over a 1- to 3-h period. Measurements of 132 se eds naturally voided by Panamanian tamarins average 11.2 mm in length and 0.3 g. The greatest number of large seeds contained in the digesti ve tract of a single animal at one time was 13. In the case of moustac hed tamarins, we collected 220 seeds. Average seed length is 11.9 mm a nd average seed weight is 0.3 g. At the time of capture, one animal ha d 26 seeds in its digestive tract. In both tamarin species, there is e vidence of sex-based differences in feeding behavior. Adult female mou stached and Panamanian tamarins swallowed and voided seeds of larger s ize than adult males did. Seed size is positively correlated with pulp weight (p < .001), therefore females were selecting food items with h igher nutritional rewards than adult males did. Given their small body size and relatively short digestive tract, why do tamarins swallow su ch large seeds? Although several explanations are possible, we propose that the large number and size of undigested seeds continuously passi ng through the tamarin gut serve a curative role in mechanically dislo dging and expelling intestinal parasites-Ancanthocephala (spiny-headed worms)-from their digestive tracts.