Why Do Tamarins Swallow Such Large Seeds? A Response to Heymann's Commentary

Abstract

In a manuscript published several years ago in the International Journal of Primatology we (Garber and Kitron International Journal of Primatology, 18, 523-538, 1997) offered two hypotheses -a feeding efficiency hypothesis and a curative function hypothesis- to account for the fact that several, if not all, species of tamarin monkeys (Saguinus) commonly swallow very large seeds (mean seed length 1.12-1.47 cm depending on the tamarin species) that pass through their digestive tract intact. Recently, Heymann (2013), using data from Knogge and Heymann (Folia Primatologica, 74, 33-47, 2003), Müller (2007), and Wenz et al. (Parasitology, 137, 675-684, 2010), attempted to test the curative function hypothesis and argued that there was no support for the contention that seeds passing through the tamarin gut acted to dislodge or expel intestinal parasites. Here we respond to Heymann's commentary. Although we acknowledge the difficulties of testing self-medication hypotheses on wild primates, we also point out that using data sets not originally designed to test such hypotheses directly limits the strength of Heymann's analyses. Moreover, we postulated that the mechanical advantage provided by seeds in expelling parasites was based on the number of large seeds present in the tamarin gut and the volume of seeds present in the tamarin gut, and not simply on whether fecal samples did or did not contain seeds. Finally we question why Heymann (2013) set a threshold for seed length in his analyses at ≥0.5 cm when based on his own data (Knogge and Heymann Folia Primatologica, 74, 33-47, 2003) the mean length of seeds voided by his tamarin study groups exceeded 1.7 cm. We commend Heymann for advancing this discussion; however, we feel that given our current state of knowledge the curative function hypothesis remains a viable explanation to account for seed swallowing in wild tamarins. © 2013 Springer Science+Business Media New York.