Niels A. Andersen

Nonshivering Thermogenesis in Marsupials: Absence of Thermogenic Response to β3-Adrenergic Agonists

The status of nonshivering thermogenesis (NST) in marsupials remains controversial. Although morphological studies have failed to find evidence for the presence of brown adipose tissue (BAT) in adults or juveniles of species from all extant families of marsupial, a number of studies have investigated the metabolic response of marsupials to noradrenaline (NA) and yielded conflicting results. In eutherian mammals, NA stimulates NST in BAT by acting on beta 3-receptors, and in the experiments reported here we investigated the response of adult and juvenile brush tail possums (Trichosurus vulpecula), a Brazilian opossum (Monodelphis domestica), adult and juvenile red-necked (Bennetts) wallabies (Macropus rufogriseus) and the laboratory rat to selective beta 3-agonists (ICI D7114 and BRL 35135) and to NA. Wallabies were tested with the beta 3-agonists only. Although NA and both beta 3-agonists caused an 85% increase in oxygen consumption in rats, there was no significant effect on any of the marsupials. These results clearly indicate no beta 3-stimulated NST in these marsupials. All reports of metabolic responses to NA are from macropods, and a recent study demonstrates that NA and other alpha-adrenergic agonists stimulate thermogenesis in a small macropod, the bettong (Bettongia gaimardi), by acting on alpha 1-receptors. Thermogenic responses to NA seems to be restricted to macropods, showing the danger of characterising the response of any one marsupial species as being representative of marsupials as a group.

Reproductive strategies of the short-beaked echidna – a review with new data from a long-term study on the Tasmanian subspecies (Tachyglossus aculeatus setosus)

The short-beaked echidna is the most widely distributed endemic Australian mammal, and echidnas from different geographic areas differ so much in appearance that they have been assigned to several subspecies. In this paper, we present data obtained from free-ranging echidnas in southern Tasmania, and compare this with studies from other parts of Australia. In Tasmania mating occurs between early June and mid-September, and throughout Australia the normal breeding season lies within these limits. In echidnas from the more easterly parts of Australia reproduction closely follows hibernation, with Tasmanian echidnas showing a significant overlap between hibernation and reproduction. There is intense competition between males, and female echidnas from Tasmania show multiple matings. There are significant differences between echidnas from different areas of Australia in the use of nursery burrows and maternal care. One of the most dramatic differences is in duration of lactation: echidnas from Kangaroo Island wean the young at 204–210 days, but in Tasmania weaning occurs at 139–152 days, even though the masses of the young at weaning are comparable.

The echidna manifests typical characteristics of rapid eye movement sleep

The failure to identify rapid eye movement sleep (REMS) in an early study of the echidna at an unmeasured ambient temperature (T(a)) was unexpected, as its brain stem structures resemble those that generate REMS in other mammals. However, typical mammalian REMS was evident in echidnas exposed to several T(a)s. The parallel presence of REMS in birds points to its reptilian origin.

Modification of macrophage response to lipopolysaccharide by fetuin.

The physiological role(s) of fetuin, a protein present in plasma and many tissues of developing animals at levels much higher than in the adult, is unknown. Here we show that fetuin can modify the responses of macrophages to lipopolysaccharide (LPS) stimulation. At concentrations of fetuin in the medium, corresponding to fetal levels of this protein in plasma, the production and secretion of interleukin 1beta (IL-1beta) and nitric oxide (NO) is almost abolished, tumour necrosis factor-alpha (TNF-alpha) reduced, while that of IL-6 is not affected. On the other hand, concentrations of fetuin corresponding to adult plasma levels (i.e. 40-60 mg/100 ml) were without much effect on macrophage synthesis and secretion of these cytokines.

The life history of an egg-laying mammal, the echidna (Tachyglossus aculeatus)

ABSTRACT Echidnas have a low metabolic rate, and energy expenditure is reduced even further by the use of torpor and hibernation. Thus, echidnas appear to lie at the slow extreme of the fast–slow continuum, and this is reflected in many aspects of echidna life history: a long life, a long lactation period, and a single young that matures late. Reproductive activity occurs in mid-winter, shortly after arousal from hibernation. After a pregnancy of about 3 weeks the female lays a single egg into her pouch that hatches after 10–11 d. Initially, the young is incubated in the pouch. Later, it is left in the nursery burrow while the mother forages for ants, termites, and other invertebrates. Lactation lasts for 150–200 d, the duration differing significantly between geographic regions. Growth rates during late lactation are very high, and, when weaned, the young has reached about 40% of adult mass. The young loses mass before entering its first hibernation, which extends from early autumn to late spring. The young echidna reaches adult mass after about 3–5 years.

Patterns of Hibernation of Echidnas in Tasmania

We present new data showing detailed records of the patterns of hibernation and reproduction of free living echidnas. As in other hibernators echidnas show periodic arousals the frequency of which changes with the season. These periodic arousals appear to be triggered by rises in ambient temperature, and although solitary, echidnas in the study area tend to arouse at the same time. Males enter hibernation in late summer or early autumn, and the final arousal occurs at about the winter solstice. Reproductive females enter and arouse from hibernation slightly later than males, mating nearly immediately on arousal while non-reproductive animals may hibernate until October. This means that adult echidnas are active and foraging during the coldest part of the year.

Cooling rates and body temperature regulation of hibernating echidnas(Tachyglossus aculeatus)

SUMMARY Echidnas (Tachyglossus aculeatus) are amongst the largest deep hibernators, but it is difficult to get them to hibernate normally under laboratory conditions. We measured body temperature (Tb) in 14 free-ranging echidnas using implanted data-loggers. Cooling during entry into hibernation bouts followed a Newtonian cooling curve, and conductances calculated from cooling curves were identical to those observed in cold exposed euthermic echidnas. Comparison with a reference soil temperature demonstrated that echidnas showed behavioural thermoregulation during hibernation; early in the hibernation season echidnas preferred to hibernate in cool areas, while during the coldest months they moved to warmer hibernacula, giving a preferred Tb in the range 8–10°C. Thermal buffering against excessive variation in Tb may be as important as maintaining a low Tb.

Field energetics of free-living, lactating and non-lactating echidnas (Tachyglossus aculeatus).

We measured daily energy expenditure (DEE) and water turnover rates in lactating and non-lactating short beaked echidnas (Tachyglossus aculeatus) using the doubly labelled water technique during the lactation period in spring. Reproductively inactive echidnas were on average significantly heavier (median: 3354 g; range: 2929-3780 g; N=4) than lactating females (median: 2695 g; range: 2690-2715 g; N=3) during the equivalent time period. The median water flux rate of lactating echidnas (152 ml day(-1); range: 120-198 ml day(-1)) did not differ significantly from that of non-lactating females (170 ml day(-1); range: 128-227 ml day(-1)). The median DEE of echidnas that were lactating was 645 kJ day(-1) (range: 581-850 kJ day(-1)), which was not different from the median DEE of non-reproductive control females (763 kJ day(-1); range: 720-766 kJ day(-1)). Lactating females somehow compensate for the energy costs of milk production, resulting in a daily energy budget that is not different from that of non-reproductive females. At least part of their energy minimising strategy could involve the use of moderate heterothermy, allowing a greater proportion of daily energy expenditure to diverted to milk production.

Spatial ecology of a ubiquitous Australian anteater, the short-beaked echidna (Tachyglossus aculeatus)

Abstract The only specialized ant-eating mammal in Australia and New Guinea is the egg-laying short-beaked echidna (Tachyglossus aculeatus), and this single species occurs throughout Australia in a wide range of habitats. Despite the diversity of habitats and density and distribution of prey species, home-range sizes throughout Australia seem remarkably similar. We radiotracked echidnas in a population in Tasmania over a 13-year period and calculated home-range sizes using the fixed kernel method and the minimum convex polygon method. No relationship was found between body mass and home-range size, and mean annual home-range size of males (90% kernels) was 107 ha ± 48 SD, twice that of females (48 ± 28 ha). Male home ranges overlapped considerably and also overlapped with those of several females. The echidna follows the pattern seen in many solitary eutherian mammals: both sexes are promiscuous, and males have larger home ranges than females. Echidnas show a high degree of home-range fidelity but can make rare excursions out of their normal area. Hibernating echidnas move between shelters during their periodic arousals, resulting in home-range sizes similar to those of the active period. Consistent with their very low metabolic rate, echidnas have home-range sizes considerably smaller than predicted for carnivorous or omnivorous mammals. Examination of data from other ant-eating mammals shows that as a group anteaters not only have smaller than predicted home ranges but they depart significantly from the normal relationship between home-range size and body mass.

Descriptive Study of the Diaphragm and Lungs in the Short-Nosed Echidna, Tachyglossus aculeatus (Mammalia: Monotremata)

ABSTRACT