β-caryophyllene in the skin secretion of the Australian green tree frog, Litoria caerulea: an investigation of dietary sources

Abstract

Uptake of noxious and toxic compounds from the diet and their subsequent concentration in integumentary glands is an important step in the defence strategy of many frog species. In this study we show that the Australian green tree frog, Litoria caerulea White, is capable of sequestering β-caryophyllene (a prominent component of the parotoid gland secretion of wild frogs), and most probably other terpenes, from its diet. Animals fed caryophyllene-dosed crickets rapidly acquired the compound in high quantities after only one feeding. Furthermore, dietary analysis of wild-caught animals identified a major source of caryophyllene (the spur-throated grasshopper) in the frogs' diet. Although the ecological significance of this uptake system has not been clarified, the presence of terpenes in the parotoid gland secretions of L. caerulea is interesting when viewed in terms of their wide spectrum of bioactivity and abundance in the environment.