Role of detoxification of plant secondary compounds on diet breadth in a mammalian herbivore, Trichosurus vulpecula

Theory predicts that mammalian herbivores detoxify different classes of plant secondary compounds via separate metabolic pathways and that generalist herbivores maintain broad diet breadth to avoid overloading individual detoxification pathways. We tested the hypothesis that a generalist marsupial herbivore, the common brushtail possum, Trichosurus vulpecula. can maintain a higher intake of food when allowed to select from two diets containing different profiles of secondary compounds (phenolics and terpenes) than when given access to the diets individually. Diets consisted of a fruit and vegetable mash to which was added ground leaves of either Eucalyptus melliodora or E. radiata. E. melliodora and E. radiata differ in their concentrations and types of secondary compounds. Brushtail possums include these eucalypt species as parr of their natural diet. We measured food consumption and detoxification metabolites of possums on these diets. Consistent with the hypothesis, animals presented with a choice of both diets consumed more food than animals given diets singly. One of the two indicators of detoxification, acid load in urine, differed significantly between diets while the other, glucuronic acid, did nor. These results provide partial support for the hypothesis that diet breadth is governed by detoxification abilities.