Temperature regulation in the echidna (Tachyglossus aculeatus)

Abstract

The echidna (Tachyglossus aculeatus) maintained a body temperature of 30.7"C f 1.03 s.d. ( N = 23) at ambient temperatures (TA) between 0 and 25°C.It may, however, also become hypothermic at low TA. At T*=3O0C or above the echidna became hyperthermic. The thermoneutral range was about 20-30°C. At low TA the metabolic rate might be increased several fold. The thermal conductance was at a minimum at TA = 20"C, and was not further reduced at lower TA. At higher TA the thermal conductance increased up to five-fold. The evaporation showed little change with increasing TA. At the highest TA we used (33°C) the evaporation on the average accounted for the dissipation of only about one-third of the metabolic heat produced. These findings suggest that the echidna, although it can maintain its body temperature at low ambient temperature, cannot rely upon evaporation as the major avenue for heat loss at high ambient temperature.The egg-laying mammals, echidna and platypus, are usually described as physiologically primitive in regard to their temperature regulation. This concept is founded upon early measurements which showed that their body temperature is lower than the usual range of placental mammals, and they were therefore considered as intermediate between "warmblooded and "cold-blooded animals. For example, occasional measurements made in the last century on echidna yielded a body temperature of some 28" to 32°C. It was therefore concluded that echidna follows its primitive anatomy by placing itself between the high temperature level of "real" mammals (about 38°C) and the "cold-blooded reptiles.The interesting study of thermal adjustment in monotremes and marsupials published by C. J. Martin in 1903 contributed the first detailed account of respiratory metabolism and thermoregulation in these mammals. It concluded: "Echidna is the lowest in the scale of warm-blooded animals. Its attempts at homoeothermism fail to the extent of 10°C when the environment varies from 5" to 35°C." This conclusion has been quoted, simplified, and rephrased in numerous texts and papers. Further support of the concept of an "ascending evolutionary order" was expressed by Robinson ('54) who observed the reactions to high temperature of the J. CELL. PHYSIOL., 67: 63-72. two extant monotremes as well as six marsupials. However, as far as we know, since Martin's paper there have been no studies of the temperature regulation in the echidna over a wide range of ambient temperatures, and we therefore found it desirable to study three individuals available to us. The results show that the echidna in some respects is an excellent temperature regulator, in other respects less capable, but probably no more so than many "higher" mammals. MATERIALS AND METHODS Animals.Three echidnas (spiny anteater, Tachyglossus aculeatus) were obtained through an Australian animal dealer. The original locality of capture is not known. They weighed between 2.5 and 3.5 kg and were apparently in good condition on arrival. Over a period of two months we determined...

Hibernation in a monotreme, the echidna (Tachyglossus aculeatus)

“…1). These results, the first from echidnas free-ranging in their natural habitat, confirm the findings of studies on captive animals (Schmidt-Nielsen et al, 1966;Augee and Ealey, 1968). The animals were active from late morning for most of the day and, sometimes, into the night as well.…”

“…The short-beaked echidna (T. aculeatus) occurs throughout Australia and in parts of Papua-New Guinea and is the only native mammal in Australia whose distribution may be said to be continent-wide (Griffiths, 1968), a distribution that implies great adaptability to habitats as diverse as hot inland deserts, mild coastal woodlands and cold alpine meadows. Echidnas have long been known to be heterothermic (Martin, 1902;Schmidt-Nielsen et al, 1966;Augee and Ealey, 1968) yet there has been no previous study of their thermal relations under field conditions.…”

Reexamining Echidna Physiology: The Big Picture forTachyglossus aculeatus acanthion

“…Our measured basal T b of 29.5°C for Western Australian echidnas was 0.6 -2.9°C lower than other basal T b estimates for this species (at T a between 23 and 30°C; Martin 1903;Warlow 1914;Schmidt-Nielsen et al 1966;Augee 1976;Dawson et al 1979;Frappell et al 1994). It is unclear if this reflects differences between sub-species (e.g.…”

“…Robinson (1954), McMurchie and Raison (1975) and Augee (1976) also subsequently concluded that short-beaked echidnas are poor homeotherms, unable to maintain a constant T b over fluctuating T a . However, Schmidt-Nielsen et al (1966) concluded that echidnas are generally very effective thermoregulators, especially at low ambient temperatures, as did McNab (1984); echidnas maintained T b within the usual range (30-31°C) even at T a as low as 0°C, although T b increased by several degrees when exposed to high T a (30°C or above). Dawson and Hulbert (1970) argued that the pattern of metabolism/endothermy/homoethermy of mammals is a distinct jump from the reptilian pattern, and differences between monotremes, marsupials and placentals need not reflect phylogenetic patterns.…”

“…They apparently lack sweat glands (Martin 1903;Schmidt-Nielsen et al 1966;Augee 1976), andMartin (1903) concluded they lack vasomotor adjustments (e.g. vasoconstriction, vasodilation).…”