Chemical signals in the echidna: differences between seasons, sexes, individuals and gland types

Seasonally reproducing animals show many behavioural and physiological changes during the mating period, including increased signalling for mate attraction. Mammals often rely on chemical signals for communication and coordination of mating and other social behaviours, but our understanding of the subtleties and functions of mammalian signalling could be increased with more input from non-model systems. We used gas chromatography–mass spectrometry and non-parametric statistics to investigate the volatile and non-volatile composition of odorous secretions in an egg-laying mammal (monotreme), the short-beaked echidna Tachyglossus aculeatus. We collected a total of 778 odorant samples from 69 wild, sexually mature individuals over 3 years at our field site in southern Tasmania. Animals were sampled during the breeding and non-breeding seasons, as well as during hibernation. Odorants included swabs from the cloaca and ‘waxy’ secretions from putative scent glands in the cloacal wall and at the base of the spurs. Chemical profiles varied between different gland secretions and by sex and season. Female spur and cloacal wax secretion profiles had higher relative abundances of sterols, whereas male wax secretion profiles had more long chain fatty acids. Male spur secretions changed significantly during the mating season and could function in intra-sexual competition or female mate choice. Echidna scent gland secretions also varied between individuals, suggesting olfactory cues could be used for individual recognition. Our results indicate that echidna secretions contain information that could be used by individuals to attract and locate mates during the breeding season. We also provide evidence for the potential importance of compounds traditionally classified as ‘non-volatile’, including sterols and fatty acids, as cues for individual recognition or mate assessment.