The red tree frog Litoria rubella is distributed throughout the centre and north of Australia. There is some zoological evidence that there are different populations of this frog throughout Australia, but it is not known whether (i) these are separate species or subspecies, or (ii) the time scale over which these changes in population have occurred.

The glandular secretion of Litoria rubella may be obtained by the benign method of electrical stimulation. The secretion contains a number of peptides of the tryptophyllin family [e.g. 1-3] that may be separated by HPLC and identified by FAB mass spectrometry. These peptides are thought to be neurotransmitters. Specimens of Litoria rubella were collected from a number of locations throughout Australia, and their peptide content analysed by mass spectrometry. These results indicated that there are at least four major populations of this frog throughout Australia, i.e. they show different and reproducible peptide profiles. Of particular interest is the population on the eastern seaboard of Queensland which shows a gradual change in peptide content from Brisbane to Cairns.