SPECIFICITY OF TANNIN-BINDING SALIVARY PROTEINS RELATIVE TO DIET SELECTION BY MAMMALS

The tannin-binding specificity of salivary proteins in several mammals was investigated as a possible explanation for observed food habits. Moose (Alces alces) and beaver (Castor canadensis) produce salivary proteins that only bind the linear condensed tannins common in their preferred foods, such as willow, aspen, or birch. The mule deer (Odocoileus hemionus), which has a more generalized diet, produces salivary proteins that bind linear and branched-chain condensed tannins and gallotannins, but not an ellagitannin. The omnivorous black bear (Ursus americanus) produces salivary proteins that bind all types of tannins. In feeding trials beaver and mule deer were fed tannins that were not bound by salivary tannin-binding proteins in the in vitro assays. The results confirmed that these tannins reduce digestibility more than tannins that are bound by salivary proteins. Thus, salivary tannin-binding proteins are not always generalized scavengers of dietary tannins, but can be very specific for the types of tannins that are consumed in the preferred diet. The diversity of tannin chemistry and the specificity of salivary tannin-binding proteins must be considered in optimal foraging studies and in cost-benefit models of herbivore diet selection.