Mechanisms of Toxin Resistance by Wild Mammalian Herbivores

Some wild vertebrate herbivores are able to ingest potentially toxic plants. However, the mechanisms that facilitate toxin tolerance are relatively unknown in free-ranging vertebrate herbivores. We hypothesized that one mechanism of toxin tolerance is regulated absorption of ingested toxins resulting in excretion of unchanged toxins in feces and low blood exposure to toxins. We tested this hypothesis using free-ranging moose (Alces americanus) in Isle Royale National Park in Lake Superior, Michigan. These moose consume large amounts of balsam fir (Abies balsamea) that contains high concentrations of plant secondary metabolites (PSM), which are toxic to most herbivores. To assess regulated absorption, we measured concentrations of unchanged monoterpenes in fecal samples of moose and in paired samples of balsam fir using gas chromatography. Understanding the mechanisms of how herbivores regulate and tolerate toxins may offer vital information that could lead to predicting and managing drug tolerance in humans, pest species, and bacteria