Abstract
Tannins and essential oils are well recognised as antiherbivore compounds. We investigated the relative effectiveness of the polyphenol, tannin, and the essential oils, 1,8-cineole and pine oil, as feeding deterrents against western grey kangaroos. Both groups of secondary metabolites are naturally abundant in many Australian plants. These three metabolite groups were incorporated separately or together into standard pellets for presentation to kangaroos, and their behaviour (sequence of food choice and feeding time) and amounts consumed were observed. The control (with no secondary metabolites) was much preferred. There was a sharp reduction in the ingestion of pellets containing tannins, 1,8-cineole or pine oil. Combinations of the metabolites resulted in almost no consumption. In association with tannin, pellets containing either 1,8-cineole or pine oil were as effective deterrents as both combined. There was a strong correlation between time spent feeding on the different diets and the amount of food consumed, although the rate of intake was markedly slower when secondary metabolites were present. Behavioural observations showed that the amount of food ingested is initially guided by the presence/absence of essential oils, apparently detected by smell, and later by the presence/absence of tannins, by taste. Both groups of secondary metabolites work in concert by stimulating different senses that minimise herbivory by marsupials, such as the western grey kangaroo, and help to explain their abundance in the Australian flora.
Highlights
Tannins and essential oils co-occur in several families well represented, if not dominant, in the Australian flora and elsewhere, especially in the families Lamiaceae, Mimosaceae, Myrtaceae, and Rutaceae [1,2,3,4]
Pine oil and 1,8-cineole were added at a concentration of 2% pellet dry weight, while tannin was added at 10% pellet dry weight
When individual essential oils were combined with tannin, consumption was
Summary
Tannins (polyphenolics) and essential oils (terpenoids) co-occur in several families well represented, if not dominant, in the Australian flora and elsewhere, especially in the families Lamiaceae, Mimosaceae, Myrtaceae, and Rutaceae [1,2,3,4]. These secondary plant metabolites are well established as antiherbivore chemicals in many parts of the world [3,5,6]. Formylated phloroglucinol metabolites (non-volatile combinations of condensed tannins and terpenes) are potent antifeeding chemicals in eucalypts, the dominant tree in Australian forests and woodlands (Myrtaceae [14])
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