HOW HERBIVORES TRACK VARIABLE ENVIRONMENTS - RESPONSE TO VARIABILITY OF PHYTOTOXINS

The concentration of toxins in plants can vary with plant phenology an d environmental factors. Changes in toxicity may or may not be associa ted with changes in plant flavor. These factors may make it difficult for herbivores to avoid toxic plants. We conducted three experiments c oncerning animals' ability to detect toxins. In experiment 1, we exami ned whether animals familiar with a tastable toxin on food would adjus t intake when toxin concentrations changed. Lambs were initially offer ed oats with either a low, medium, or high concentration of lithium ch loride (LiCl; a salty-tasting toxin). Later, when all lambs were offer ed oats with the medium concentration of LiCl, lambs that were conditi oned with the low LiCl concentration decreased intake while lambs cond itioned with the high LiCl concentration increased intake. In experime nt 2, we examined flavor aversions formed when animals sampled food wi th two flavor levels prior to illness. Lambs initially ate the same am ount of barley with a low and with a high concentration of either sodi um saccharin (a sweet flavor) or aluminum sulfate (a bitter flavor). L ambs then received a mild dose of LiCl. Later, when lambs were offered a choice between barley with either a low or high flavor concentratio n, lambs preferred the barley with the low flavor concentration. Exper iment 3 examined how variable toxicity affected intake when the flavor remained constant. Lambs were initially offered oregano-flavored barl ey and then received a dose of LiCl. Lambs received either a medium do se, a high dose, or a dose that varied randomly among low, medium, or high amounts of LiCl. Lambs in the medium dose group ate more oregano- flavored barley at the end of the trial than did lambs in either of th e other groups.