Ecological example of conditioned flavor aversion in plant-herbivore interactions: Effect of terpenes of Eucalyptus leaves on feeding by common ringtail and brushtail possums

We investigated the hypothesis that feeding deterrence of common ringtail p ossums (Pseudocheirus peregrinus) and common brushtail possums (Trichosurus vulpecula) by Eucalyptus terpenes (in this case 1,8-cineole) is a result o f a conditioned flavor aversion (CFA), due to die association of terpenes w ith postingestive effects of another group of Eucalyptus toxins, the diform ylphloroglucinol compounds (DFPCs). Wild-caught common ringtail and common brushtail possums showed a dose-dependent reduction in food intake when 1,8 -cineole was added to the diet. However, after continued exposure over 12 d ays to increasing amounts of cineole in the diet, both species substantiall y increased their intakes of cineole relative to control animals. This indi cated that the aversion to cineole was a conditioned response rather than a physiological limitation in their ability to detoxify terpenes. Subsequent exposure to a diet including both cineole and jensenone (a simple DFPC als o found in Eucalyptus and considered to cause postingestive emesis) in corr esponding amounts was able to recondition the dose-dependent aversion. Cons equently, animals that had been given jensenone showed an aversion to cineo le-rich diets that matched the behavior of animals in the control group. Th is supported our hypothesis that the effect of terpenes on feeding of these marsupial folivores on Eucalyptus is due to a CFA. Possums can cope with l evels of terpenes in the diet that far exceed those occurring naturally. Th e role of terpenes in marsupial folivore-Eucalyptus interactions appears to be to act as a cue to levels of toxic DFPCs in the leaves, rather than act ing as toxins in their own right.