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Illiger, 1811
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The Short-beaked Echidna (Tachyglossus aculeatus), also known as the spiny anteater, is one of the four living species of echidna and the only member of the genus Tachyglossus. The Short-beaked Echidna is covered in fur and spines and has a distinctive snout and a specialised tongue which it uses to catch termites and ants at a great speed. Like the other extant monotremes, the Short-beaked Echidna lays eggs; the monotremes are the only group of mammals to do so.
The species is found throughout Australia and in coastal and highland regions of New Guinea. It is not threatened with extinction, however human activites such as hunting and habitat destruction and predatory species and their parasites introduced by humans have had negative impacts on the species distribution.
Taxonomy and evolution
The Short-beaked Echidna was first described by George Shaw in 1792. He named the species Myrmecophaga aculeata, thinking it might be related to the South American anteater. Since Shaw first described the species, its name has undergone four revisions: from M. aculeata to Ornithorhynchus hystrix, Echidna hystrix, Echidna aculeata and, finally, Tachyglossus aculeatus, the Short-beaked Echidna.[1] The name Tachyglossus means "quick tongue", in reference to the speed the echidna uses its tongue to catch ants and termites.
The Short-beaked Echidna is the only member of its genus, sharing the family Tachyglossidae with the extant species of the genus Zaglossus that occur in New Guinea. Zaglossus are much larger than Tachyglossus. Species of the Tachyglossidae are mammals that lay eggs, and they and the related family Ornithorhynchidae are the only living monotremes in the world.
There are five subspecies of the Short-beaked Echidna, each found in a different geographical location. The subspecies also vary from each other in terms of hairiness, spine length and diameter, and size of grooming claw on the hind feet.
- T. a. multiaculeatus is found on Kangaroo Island;
- T. a. setosus is found on Tasmania and some islands in Bass Strait;
- T. a. acanthion is found in Northern Territory and Western Australia;
- T. a. aculeatus is found in Queensland, New South Wales, South Australia and Victoria;
- T. a. lawesii is found coastal regions and the highlands of New Guinea and potentially in the rainforests of Northeast Queensland.[2]
Physical description
Short-beaked Echidnas are typically 30 to 45 centimetres in length, have a 75-millimetre snout, and weigh between two and five kilograms. The Tasmanian subspecies, T. a. setosus, is larger than its Australian mainland counterparts. As the neck is not externally visible, the head and body appear to merge together. The ear holes on either side of the head with no external pinnae. The eyes are small and located at the base of the wedge-shaped snout. Both the nostrils and the mouth are located at the distal end of the snout; the mouth of the Short-beaked Echidna cannot open wider than 5 mm.[3] The body of the Short-beaked Echidna is, with the exception of the underside, face and legs, covered with cream-coloured spines. The spines, which may be up to 50 mm long, are modified hairs. Insulation is provided by fur between the spines, which ranges in colour from honey to a dark reddish-brown and even black; the underside and short tail are also covered in fur. Its fur may sometimes be infested with what is said to be the world's largest flea, Bradiopsylla echidnae, which is about 4 mm long.
The limbs of the Short-beaked Echidna are adapted for rapid digging, having short limbs and powerful claws. The claws on the hind feet are elongated and curve backwards to enable cleaning and grooming between the spines. Like the Platypus the male Short-beaked Echidna has a spur on the hind foot; unlike the Platypus the spur is blunt, and the venom gland is not developed. Its low body temperaature, which is between 30 and 32 degrees celcius, is another characteristic it shares with the Platypus. The Short-beaked Echidna, like all monotremes, has one orifice for the passage of faeces, urine and reproductive products. The male has internal testes, no external scrotum and a highly unusual penis with four knobs on the tip. The pregnant female develops a pouch on its underside.
The musculature of the Short-beaked Echidna has a number of unusual aspects. The panniculus carnosus is an enormous muscle that is just beneath the skin and covers the entire body. By contraction of various parts of the panniculus carnosus, the Short-beaked Echidna can change shape – the most characteristic shape change is rolling itself into a ball when threatened, protecting the belly and presenting a defensive array of sharp spines.
The musculature of the face, jaw and tongue is also specialised to allow the Echidna to feed. The tongue of the Short-beaked Echidna is the animal's sole means of catching prey and can protrude up to 180 mm outside the snout. The tongue is sticky because of the presence of glycoprotein-rich mucous, which both lubricates movement in and out of the snout and helps to catch ants and termites as they stick to it. Protrusion of the tongue is achieved by contraction of circular muscles which deform the tongue and force it forward, and contraction of two genioglossal muscles attached to the caudal end of the tongue and to the mandibles. The protruded tongue is stiffened by the rapid flow of blood, allowing it to penetrate wood and soil. Retraction requires the contraction of the sternoglossi, two internal longitudinal muscles. When the tongue is retracted, the prey is caught on backward-facing keratinous "teeth" located along the roof of the buccal cavity. The tongue moves with great speed, and has been measured to move in and out of the snout 100 times per minute.[4]
The Short-beaked Echidna has numerous physiological adaptations to aid its lifestyle. Because the Short-beaked Echidna burrows, it can tolerate very high levels of carbon dioxide in inspired air, and can voluntarily remain in situations where carbon dioxide concentrations are high. The ear is sensitive to low frequency sound, which is probably ideal for detecting sounds emitted by termites and ants underground. The leathery snout is covered in mechano- and thermoreceptors, which provide information about the surrounding environment.[5] The Short-beaked Echidna has a well-developed olfactory system, which may be used to detect mates and prey. It also has a well-developed optic nerve and has been shown to have visual discrimination comparable to a rat.
Reproduction
The solitary Short-beaked Echidna looks for a mate between May and September; the precise timing of the mating season varies with geographic location. Both males and females give off a strong odour during the mating season. The male locates and pursues the female, and trains of up to seven males may follow a single female. This courtship ritual may last for up to four weeks; however, the length of the courtship period also varies with location. Before mating the male smells the female, paying particular attention to the cloaca. The male is often observed to roll the female onto her side and then assumes a similar position so that the two animals are abdomen to abdomen.
Fertilisation takes place in the oviduct. Gestation takes between 21 and 28 days, and during this period the female constructs a nursery burrow. Following the gestation period, a single rubbery-skinned egg between 13 and 17 millimetres in diameter is laid directly into a small, backward-facing pouch which has developed on the abdomen of the female. Ten days after it is laid, the egg hatches within the pouch. The embryo develops an egg tooth during incubation that it uses to tear open the egg; the egg tooth disappears soon after hatching.
When the egg hatches, the hatchling is about 1.5 mm long and weighs between 0.3 and 0.4 g. The hatchling attaches to the milk areolae or milk patch, which is a specialised patch on the skin that secretes milk, since monotremes do not have nipples. The way the young imbibes the milk is unknown, but they ingest large amounts of milk during a feeding period, since the mother may leave them in the burrow unattended for between five and ten days. The principle components of the milk are fucosyllactose and saialyllactose; it is also high in iron which gives it a pink colour. Juveniles are eventually ejected from the pouch at around two to three months of age because of the continuing growth of their spines. Suckling gradually decreases until the juvenile is weaned at about 6 months of age. The duration of lactation is about 200 days, and the young leaves the burrow between 180 and 240 days.
The age of sexual maturity is not known with confidence, but may be two to three years. The Short-beaked Echidna does not breed yearly. They probably live to 20 years in the wild, and captive specimens have been known to live longer.
Ecology and behaviour
No systematic study of the ecology of the Short-beak Echidna has been published; however, studies of aspects of their ecological behaviour have been made. Short-beaked Echidnas live alone and apart from the burrow created for rearing young; they have no fixed shelter or nest site. They do not have a home territory, but range over a wide area. The Short-beaked Echidna is typically active in the daytime; however, they are ill equipped to deal with heat as they have no sweat glands and do not pant. Thus in warm weather they must change their pattern of activity, becoming crepuscular or nocturnal. They can tolerate cold temperatures, and in very cold regions, they hibernate for the winter months.
The Short-beaked Echidna locates its food by smell and by using sensors in the tip of its snout. The Short-beaked species regularly feasts on ants or termites, thus earning its common nickname, the spiny anteater. They are powerful diggers, using their clawed front paws to dig out prey or create burrows for shelter. They may also rapidly dig themselves into the ground when they are in danger if they cannot find cover.
The Short-beaked Echidna can live anywhere that has a good supply of food. They are most common in forested areas where there are abundant termite-filled fallen logs. In agricultural areas they are most likely to be found in uncleared scrub; they may also be found in grassland, arid areas, and in the outer suburbs of the capital cities.
Conservation status
The Short-beaked Echidna is common throughout most of temperate Australia and lowland New Guinea – it is not listed as endangered by any agency. In Australia, the number of Short-beaked Echidna's has not been as affected by land clearing as other species, since they do not require specialised habitat, just a good supply of ants and termites. Despite their spines they are preyed upon by birds of prey, Tasmanian Devils, cats, foxes and dogs. They were also eaten by Indigenous Australians and the early European settlers of Australia. The most common threats to the Short-beaked Echidna in Australia are the automobile and habitat destruction leading to localised extinction. Infection with the introduced parasite Spirometra erinacei is also fatal for the Enchidna.
Captive breeding is difficult. Only five zoos have managed to breed captive Short-beaked Echidnas; however, no captive-bred young have survived to maturity. This has conservation implications for the endangered species of echidna from the genus Zaglossus, and to a lesser extent for the Short-beaked Echidna.
Cultural references
The Short-beaked Echidna is an iconic animal in Australia, appearing on the 5 cent piece. The anthropomorphic Echidna Millie was a mascot for the 2000 Summer Olympics.
Notes
- ^ Iredale, T. and Troughton, E. 1934. A checklist of mammals recorded from Australia. Memoirs of the Australian Museum 6: i–xii, 1–122
- ^ Griffiths, M.E. 1978. The Biology of Monotremes. Academic Press : New York
- ^ Murray, P.F. 1981. A unique jaw mechanism in the echidna, Tachglossus aculeatus (Monotremata). Australian Journal of Zoology 29: 1–5
- ^ Doran, G.A. and Baggett, H. 1970. The vascular stiffening mechanism in the tongue of the echidna (Tachyglossus aculeatus). Anatomical Record 167: 197–204
- ^ Iggo, A., McIntyre, A.K. & Proske, U. (1985). Responses of mechanoreceptors and thermoreceptors in skin of the snout of the echidna Tachyglossus aculeatus. Proceedings of the Royal Society of London B 223: 261–277
References
- Augee, M and Gooden, B. 1993. Echidnas of Australia and New Guinea. Australian National History Press ISBN 9780868400464
- Augee, M.L. 1983. R. Strahan Ed. The Australian Museum Complete Book of Australian Mammals. p. 8-9. Angus & Robertson ISBN 0207144540
- Griffiths, M. 1989. Tachyglossidae. Pp. 407–435 in Fauna of Australia (D. W. Walton and B. J. Richardson, eds.). Mammalia, Canberra, Australian Capital Territory 1B:1–1227.