Stewart C. Nicol

Temperature regulation in the little penguin,Eudyptula minor, in air and water

Summary1.Metabolic rate and body temperature were measured at various air and water temperatures in the little penguin.2.In air the basal metabolic rate was 4.93 W·kg−1 and body temperature was 38.4°C. The thermoneutral zone extended from 10 to 30°C.3.In water there was no thermoneutral zone. Metabolic rat increased gradually until a critical water temperature was reached at 10°C whereupon heat production increased sharply. Body temperature in water was 39.2°C.4.Little penguins in air had insulative values similar to the emperor penguin. Penguin feathers provide the major component of insulation and their function as a waterproof barrier implies relatively high rates of heat loss on land.5.Little penguins could not maintain body temperature at water temperatures below 5°C. Their small size has limited southern distribution.

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.

Cool Sex? Hibernation and Reproduction Overlap in the Echidna

During hibernation there is a slowing of all metabolic processes, and thus it is normally considered to be incompatible with reproduction. In Tasmania the egg-laying mammal, the echidna (Tachyglossus aculeatus) hibernates for several months before mating in mid-winter, and in previous studies we observed males with females that were still hibernating. We monitored the reproductive activity of radio-tracked echidnas by swabbing the reproductive tract for sperm while external temperature loggers provided information on the timing of hibernation. Additional information was provided by camera traps and ultrasound imaging. More than a third of the females found in mating groups were torpid, and the majority of these had mated. Some females re-entered deep torpor for extended periods after mating. Ultrasound examination showed a developing egg in the uterus of a female that had repeatedly re-entered torpor. The presence of fresh sperm in cloacal swabs taken from this female on three occasions after her presumed date of fertilization indicated she mated several times after being fertilized. The mating of males with torpid females is the result of extreme competition between promiscuous males, while re-entry into hibernation by pregnant females could improve the possibility of mating with a better quality male.

Sleep and metabolic rate in the little penguin,Eudyptula minor

SummaryThe effects of sleep upon metabolic rate in the little penguin were examined at thermoneutral and low temperatures in day and night experiments.Little penguins show similar electrophysiological indices of sleep to other birds. The amount of sleep increased at night due to increased frequency of sleep periods and decreased with cold exposure due to a reduction in the length of sleep periods.Sleep was associated with a slight decrease (8%) in metabolic rate when compared to quiet wakefulness in all experimental conditions. This descrease, however, represents only a marginal reduction in daily energy costs. There would be a difference of only 2.4% in the hypothetical daily energy budget of a resting little penguin if it did not sleep at all.

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.

Diving behaviour, dive cycles and aerobic dive limit in the platypus Ornithorhynchus anatinus.

We investigated the diving behaviour, the time allocation of the dive cycle and the behavioural aerobic dive limit (ADL) of platypuses (Ornithorhynchus anatinus) living at a sub-alpine Tasmanian lake. Individual platypuses were equipped with combined data logger-transmitter packages measuring dive depth. Mean dive duration was 31.3 s with 72% of all dives lasting between 18 and 40 s. Mean surface duration was 10.1 s. Mean dive depth was 1.28 m with a maximum of 8.77 m. Platypuses performed up to 1600 dives per foraging trip with a mean of 75 dives per hour. ADL was estimated by consideration of post-dive surface intervals vs. dive durations. Only 15% of all dives were found to exceed the estimated ADL of 40 s, indicating mainly aerobic diving in the species. Foraging platypuses followed a model of optimised recovery time, the optimal breathing theory. Total bottom duration or total foraging duration per day is proposed as a useful indicator of foraging efficiency and hence habitat quality in the species.

Thermoregulation, respiration and sleep in the Tasmanian devil,Sarcophilus harrisii (Marsupialia: Dasyuridae)

Summary1.Body temperature (Tb), skin temperature (Tsk), metabolic rate (MR), respiratory frequency (f), tidal volume (VT) and respiratory minute volume (E) were measured in adult Tasmanian devils during wakefulness (W), slow wave sleep (SWS) and paradoxical sleep (PS) over a range of ambient temperature (Ta) from 2–45 °C.2.The thermoneutral zone was 28.5 to 32 °C. During SWS and W shivering occurred atTas below 28.5 °C, while aboveTa=32 °C, panting occurred.3.Below the thermoneutral zone MR andTb varied cyclically. These cycles were due to alternation of SWS and PS. During PS shivering did not occur and MR fell markedly.4.Tb was very variable atTas from 12–28 °C (Fig. 4), withTb falling as low as 32.5 °C, whileTbs below 32 °C were sometimes measured at the beginning of an experiment.Tb increased at lowerTas and atTas above 28 °C. Panting commenced atTb=37 °C andTb rarely exceeded 38 °C during heat exposure.5.VT decreased with increasingTa in W, SWS and PS, but the change was less during PS (Fig. 6).6.Below the thermoneutral zone, during W and SWS, E andf increased asTa decreased while during PS, E andf were not affected byTa (Fig. 6, Table 1).7.Above the thermoneutral zone, during W and SWS, E andf increased rapidly due to panting, while during PS the panting response was weakened but not abolished (Fig. 6, Table 1).8.PS appears to have an important role in reducing energy expenditure during rest.

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.