How real are the subspecies of Tachyglossus aculeatus ? A review of geographic differences in morphology, diet, behaviour, physiology and genetics

Short-Beaked Echidnas (Tachyglossus aculeatus) are Australia’s most widespread native mammal and are found in all terrestrial environments on mainland Australia and most major islands, as well as New Guinea. Despite the obvious differences in appearance of echidnas from different areas of Australia, and their current division into five subspecies based on these differences, two mtDNA based phylogenetic studies failed to find any genetic support for the subspecies. Differences between the subspecies extend beyond variations in the hair and spines and include physical features such as the length and angle of the beak, physiological features such as use of hibernation and torpor, lactation duration and milk composition, and differences in mating behaviour and maternal care. Most of these differences appear to be directly or indirectly related to climate. Based on the fossil history and current theories of the origins of tachyglossids, the failure to find mtDNA support for the subspecies is likely to be the result of fairly recent, probably Pleistocene dispersal, consistent with immigration from New Guinea and rapid adaptation of populations to local environmental conditions. The case for recognising distinct subspecies of Tachyglossus aculeatus appears overwhelming, and some of the differences are so important I urge against making generalised statements about echidna biology if they are based on observations of one subspecies. The genetic studies do show some significant problems with the current subspecies designations: Western Australian, and probably central Australian, echidnas are not acanthion, and the dark Queensland form described as lawesii is probably not lawesii.