Herbivore experience with plant defense compounds influences acquisition of new flavor aversions

Multiple experiments were conducted with a mammalian herbivore to determine how experience with plant secondary metabolites (terpenes and tannins) influenced acquisition of new aversions to diets containing these same plant metabolites. Goats (Capra aegagrus hircus) were employed as behavioral models for this study. Twenty-four subjects were assigned to three treatment groups that received 20 days of experience with test diets: (A) terpene diet only; (B) tannin diet only; and (C) terpene and tannin diets offered singly on alternate days. In experiment 1, all subjects were offered both diets in a two-choice test to determine if experience affected diet preference. Both treatments A and B demonstrated significant preferences for the terpene diet, while treatment C subjects did not exhibit a diet preference. Both diets were offered to all subjects and immediately followed with a 150 mg/kg dose of lithium chloride (LiCl) in experiment 2. A two-choice preference test was conducted to determine if lithiuminduced toxicosis would be associated with the least familiar diet. As in experiment 1, treatments A and B preferred terpene diet while treatment C did not demonstrate a preference. Lithium chloride exposure was specifically paired with one of the test diets in experiment 3. A two-choice preference test demonstrated that treatments A, B, and C acquired aversions to tannin diet when it was paired with LiCl administration. However, terpene-paired LiCl administration did not produce an aversion to the terpene diet in treatments A and B. Treatment C preferred tannin diet when the terpene diet was paired with LiCl. A novel flavor was added to the choice of diets in experiment 4. All subjects were offered citric acid (CA), terpene, and tannin-containing diets and immediately dosed with LiCl. Subjects that acquired aversions to the tannin diet in experiment 3 continued to avoid tannin diet in experiment 4 and preferred terpene diet while eating significant quantities of the novel CA diet. Only treatment C subjects with previous terpene-paired LiCl exposures demonstrated aversions to the CA diet. These results have implications for the conduct of flavor aversion studies and the application of flavor aversion learning (FAL)