Free-ranging koalas generally feed at night; however, captive koalas are usually fed during the day in order to encourage activity for display purposes. We studied the temporal effect of feeding on body temperature of captive koalas in Queensland, to determine whether nocturnal feeding may be beneficial for koalas in warmer climates. Six adult koalas were implanted with thermal transmitters and data loggers, waxed together as a single package, to record internal body temperature. Koalas were exposed to two treatments: koalas were fed in the morning (between 0730 and 0830 hours) during the AM treatment or late afternoon (between 1700 and 1800 hours) for the PM treatment. The body temperature of koalas fed in the mornings was on average 0.5°C higher at its peak (P ≤ 0.01) when compared to koalas fed in the evening. Furthermore, the body temperature maxima of morning-fed koalas was reached ~2 h earlier in the afternoon, compared with those fed in the evening. There was no significant difference between behaviours associated with the two feeding regimes: inactivity (P = 0.840), feeding (P = 0.472) and activity (P = 0.634). We postulate that nocturnal feeding by koalas may be an adaptive mechanism that reduces diurnal heat load during times of high environmental temperatures.

Dugongs (Dugong dugon) are fully marine mammals that live independently of fresh water so must balance water and electrolytes in a hyperosmotic environment. To investigate osmoregulation, matched plasma and urine from 51 live wild dugongs were analysed for osmolality, major electrolytes (Na+, Cl−, K+), urea, creatinine, and glucose. Maximum urine osmolality (1468 mOsm kg –1) and Na+, K+, and Cl– concentrations (757, 131.3, 677 mmol L–1, respectively) indicate that dugongs are capable of concentrating urine above seawater and could potentially realise a net gain of free water from drinking seawater. However, mean urine osmolality of 925.4 (± 46.6) mOsm kg–1 suggests that mariposia is unlikely to be an important osmoregulatory mechanism. Dugongs may obtain enough preformed water from their seagrass diet and metabolic oxidation to maintain homeostasis. Mean plasma osmolality of 339.6 (± 1.8) mOsm kg–1 is higher than in the related manatees but within the range for fully marine cetaceans. Relatively high mean plasma Na+ (175.5 ± 1.7 mmol L–1) and K+ (6.9 ± 0.1 mmol L–1), as well as mean urinary Na+ (469.6 ± 22.5 mmol L–1) and K+ levels (32.5 ± 4.5 mmol L–1) may reflect a salt-rich seagrass diet. Pregnant females had higher mean plasma osmolality (355.3 ± 4.9 mmol L–1) than non-pregnant females and males (337.9 ± 1.7 mOsm kg–1), suggesting that fluid retention was not a feature of pregnancy. Further research on water intake and endocrinology will enhance our understanding of osmoregulation in dugongs.

The distribution of the koala (Phascolarctos cinereus) in Queensland is predicted to contract as a result of climate change, driven by the frequency, intensity and duration of heatwaves and drought. However, little is known about the physiological responses of this species to environmental extremes under field conditions. This study aimed to establish the efficacy of surgically implanted thermal radio transmitters and data loggers to measure the body temperature of free-ranging koalas across a range of environmental conditions and ambient temperatures. Five free-ranging koalas in southeast Queensland were implanted with thermal transmitters and data loggers waxed together as a single package. Body temperatures were recorded for variable periods ranging from 3 to 12 months. Diurnal rhythms in body temperature were detected irrespective of season. The long-term diurnal body temperature peak for all koalas occurred between 16:00 and 17:00 h and body temperature was 36.7–36.9 °C, the long-term nadir occurred between 07:00 and 08:00 h and body temperature was 35.4–35.7 °C. Koala body temperatures as low as 34.2 °C and as high as 39.0 °C were recorded. Thermolability became apparent when ambient temperatures were outside the deduced thermal neutral zone for koalas (14.5–24.5 °C): heat was accumulated during the day and dissipated during the cool of the night. While this study is the first to report on body temperature of free-ranging koalas in their normal behavioural context, further investigations are necessary to determine the physiological boundaries of the thermal niche for this species, in order to better equip models that will more accurately predict the impacts of climate change on koalas.

OBJECTIVE:Compare the use of four techniques to measure body temperature in koalas: intraperitoneal (thermal data logger and temperature sensitive radio transmitter), rectal (certified thermometer), tympanic (infrared thermometer), and hind foot (infrared camera). METHODS:The body temperature data collected concurrently from the intraperitoneal loggers were used as the benchmark in the analyses. RESULTS:The rectal, foot and tympanic methods consistently recorded lower body temperature when compared with the benchmark. There was a strong positive relationship (R2  = 0.79) between logger and rectal measurements, but no significant relationship between logger and foot or logger and tympanic measurements. CONCLUSION:Rectal measurements can be used to record internal body temperature, with the caveat that such measurements will generally register a temperature approximately 0.25°C lower than the actual intraperitoneal temperature.

The bull’s scrotum and scrotal cord vasculature has traditionally been regarded as a thermoregulatory device for maintaining optimal testicular temperature for normal spermatogenesis. This assumption has mostly been derived from discrete measurements using thermocouples with limited data correlating continuous scrotal temperature (ST) to body temperature (BT). From mid-summer to early autumn, four Wagyu bulls (9–18 months) were surgically implanted with two data loggers (DL) logging at 30 min intervals: one on the right hand side flank and the other was attached to the visceral vaginal tunic of the mid-testis. Bulls were firstly housed in a paddock (PK) for 13 days and then moved to individual pens (IP), again for 13 days. Repeated measures analysis modelled the long-term and diurnal trends in BT and ST. While both day and time of day (TOD) were significant effects for ST at both housing locations (P < 0.005), only TOD showed significance for BT at both locations (P < 0.0001). Significant effects were seen between bulls with ST (F = 167.2, P < 0.001) but not BT (F = 0.03, P = 0.863), suggestive of variation in individual bull thermoregulatory capacity. Dual peaks were observed in ST at 0500 and 2130 h when housed in PK but not IP, suggesting ST may be influenced by external stimuli such as postural or behavioural changes. Reporting concurrent and continuous BT and ST will allow further investigation into factors influencing bovine ST and should be useful in selecting bulls with high degrees of thermoregulation capacity.

Synchronous and continuous measurement of body (BT) and scrotal temperature (ST) without adverse welfare or behavioural interference is essential for understanding thermoregulation of the bull testis. This study compared three technologies for their efficacy for long-term measurement of the relationship between BT and ST by means of (1) temperature sensitive radio transmitters (RT), (2) data loggers (DL) and (3) infrared imaging (IRI). After an initial pilot study on two bulls to establish a surgical protocol, RTs and DLs were implanted into the flank and mid-scrotum of six Wagyu bulls for between 29 and 49 days. RT frequencies were scanned every 15 min, whilst DLs logged every 30 min. Infrared imaging of the body (flank) and scrotum of each bull was recorded hourly for one 24-h period and compared to RT and DL data. After a series of subsequent heat stress studies, bulls were castrated and testicular tissue samples processed for evidence of histopathology. Radio transmitters were less reliable than DLs; RTs lost > 11 % of data, whilst 11 of the 12 DLs had 0 % data loss. IRI was only interpretable in 35.8 % of images recorded. Pearson correlations between DL and RT were strong for both BT (r > 0.94, P < 0.001) and ST (r > 0.80, P < 0.001). Surgery produced temporary minor inflammation and scrotal hematoma in two animals post-surgery. Whilst scar tissue was observed at all surgical sutured sites when bulls were castrated, there was no evidence of testicular adhesion and normal active spermatogenesis was observed in six of the eight implanted testicles. There was no significant correlation of IRI with either DL or RT. We conclude that DLs provided to be a reliable continuous source of data for synchronous measurement of BT and ST.

BACKGROUND:Under predicted climate change scenarios, koala distribution in Australia is expected to be adversely affected. Recent studies have attempted to identify suitable habitat, based on models of bioclimatic regions, but to more accurately reflect the thermal tolerance and behavioural adaptations of the various regional populations, the koala's response to periods of heat stress will need to be investigated at the individual animal level.OBJECTIVE:To explore the safety and suitability of temperature-sensitive intra-abdominal implants for monitoring core body temperature in the koala.METHODS:A temperature-sensitive radio transmitter and thermal iButton data-logger, waxed together as a package, were surgically implanted into the abdominal cavity of four captive koalas. In one animal the implant was tethered and in the other three, it was left free-floating.RESULTS:After 3 months, the implants were removed and all four koalas recovered without complications. The tethering of the package in the one koala resulted in minor inflammation and adhesion, so this practice was subsequently abandoned. The free-floating deployments were complication-free and revealed a diurnal body temperature rhythm, with daily ranges of 0.4-2.8°C. The minimum recorded body temperature was 34.2°C and the maximum was 37.7°C. The difference in the readings obtained from the transmitters and iButtons never exceeded 0.3°C.CONCLUSIONS:The suitability of the surgical approach was confirmed, from both the animal welfare and data collection points of view.

Captive breeding of the short-beaked echidna (Tachyglossus aculeatus) has proven a difficult challenge; as recently as 2009, there were fewer than 10 echidnas born in captivity. We present observations of captive reproductive behaviour following video surveillance and measurements of body temperature collected from six captive female echidnas over a six-year period. In the first series of observations (2009–10) we examined the efficacy of artificial burrow boxes as possible aids for reproductive success. Females with access to burrow boxes had significantly higher levels of reproductive activity (P = 0.001), there was coincidental improvement in the production of eggs or pouch young (two eggs, one unhatched and one offspring). During 2009–10, a range of reproductive behaviours (courtship, copulation and postcopulation) were documented and analysed, as were new observations of oestrous cycle activity. Female body temperature was characteristically stable during egg incubation during this study and has the potential to be used as a tool for the assessment of reproductive status. Following initial observations, burrow boxes and infrared lamps were implemented as standard husbandry in our echidna breeding facility and the effects on reproductive success were monitored, albeit less intensively, for a further four years (2011–14). Although no direct causal effect could be ascribed, the use of burrow boxes and heat lamps coincided with a total of 13 young being born to four females in the last four years (2011–14). These female echidnas were found to be receptive at intervals throughout the breeding season, both before and after presumed incubation phases, suggesting that captive animals exhibit polyoestry. In 2012 and 2014, the same female showed evidence of producing two young from one breeding event.

We measured gas exchange of eggs and mound material as well as gas concentrations at different times during incubation in the mound nests of the salt water crocodile, Crocodylus porosus and the American alligator, Alligator mississippiensis. Oxygen consumption increased gradually during development in both species, peaking well before hatching (at approximately 80% of the incubation period in A. mississippiensis). The RE of eggs at 30 °C and at peak O2 was 0.74 in C. porosus and 0.70 in A. mississippiensis. In a typical mound nest of C. porosus, the oxygen demand of the decomposing nest itself is likely to be 4-7 times that of the clutch at the end of incubation, with a respiratory exchange ratio (RE) of about 0.9. Despite the oxygen demand of nest material, the gaseous environment of the nest is favourable for embryonic development. The lowest pO2 we measured was125 Torr in nests of C. porosus and 133 Torr in nests of A. mississippiensis, with maximum pCO2 of 22 Torr for C. porosus and 23 Torr for A. mis...

The short-beaked echidna (Tachyglossus aculeatus) is an exceptionally long-living mammal having a maximal lifespan of -50 years. This is about four times that predicted from its body mass and, consequently, its longevity quotient is ∼4.This longevity quotient is similar to two other exceptionally long-living mammalian species; the naked mole-rat (Heterocephalus glaber) and Homo sapiens. In recent times, the types of fats that make up cellular membrane have been implicated in the determination of a species' maximum lifespan. This modification of the oxidative stress theory of aging, which has been called the membrane pacemaker theory of aging, derives from the fact that polyunsaturated fats are very susceptible to lipid peroxidation whereas monounsaturated fats are resistant to peroxidation. As a test of the theory we measured the fatty acid composition of membrane lipids isolated from tissues of echidnas.We found that, as In the other long-living mammals, echidna membranes are more monounsaturated and less polyunsaturated than would be predicted from their body size and that the peroxidation Index of their membrane lipids is what their maximum longevity would predict.

In this study of body temperatures (Tb) in free ranging dromedary camels, we found that bulls in rut start the days cooler. Daily minima during rut averaged 0.6°C lower than at other times (95% CI 0.27–0.94°C) and daily maxima averaged 0.45°C higher (95% CI −0.01 to –0.91°C), increasing the daily Tb cycle. Knut Schmidt-Nielsen described a similar pattern in captive dromedaries deprived of water in hot conditions, which he interpreted as a strategy to conserve water. Our observations were made in winter and with water freely available. Dromedaries can apparently employ heterothermy for more than just water conservation. In the strenuous daily contests between rival bulls in rut, a lower Tb early in the day should extend the time for which a contestant can challenge or defend before heat stress becomes a problem. Calculations show that lowering Tb by even 0.6°C extends that time by more than 30 min, and many daily minima during rut were lower than that. Because the eventual winner of contests gains or retains a herd of females, we speculate that cooler Tb at the start of daily contests confers an advantage which translates directly into increased reproductive success.

The echidna Tachyglossus aculeatus is a monotreme mammal from Australia that is exceptionally long-living. Its documented maximum lifespan of 50 years is 3.7 times that predicted from its body mass. Other exceptionally long-living mammals (naked mole-rats and humans) are known to have peroxidation-resistant membrane composition, raising the question about echidnas. Phospholipids were extracted from skeletal muscle, liver and liver mitochondria of echidnas and fatty acid composition measured. As with other exceptionally long-living mammals, membrane lipids of echidna tissues were found to have a lower content of polyunsaturates and a higher content of monounsaturates than predicted for their body size. The peroxidation index (=peroxidation susceptibility) calculated from this membrane composition was lower-than-expected for their body size, indicating that the cellular membranes of echidnas would be peroxidation-resistant. Additionally when the calculated peroxidation index was plotted against maximum lifespan, the echidna values conformed to the relationship for mammals in general. These findings support the membrane pacemaker theory of aging and emphasise the potential importance of membrane fatty acid composition in aging and in the determination of maximum longevity.

Oxygen equilibrium curves and other respiratory-related variables were determined on blood from the flatback turtle (Natator depressus) and, for comparison, on some samples from the loggerhead turtle (Caretta caretta). The oxygen carrying capacity of the flatback turtle, 4.9-8.7 mmol l(-1) (n = 49), is at the high end of the range in diving reptiles. Oxygen affinity (P(50)) was similar in both species at 5% CO(2), ranging from 37 to 55 mmHg (43 mmHg +/- 5.3 SD, n = 24, 25 degrees C, pH 7.17) in flatbacks and 43-49 mmHg in loggerheads (46 mmHg +/- 2.0 SD, n = 7, 25 degrees C, pH 7.13), whereas at 2% CO(2), flatbacks had a higher oxygen affinity. The curves differed in sigmoidicity, with Hill n coefficients of 2.8 and 1.9 in flatbacks and loggerheads, respectively. The Bohr effect was small in both the species, consistent with results from other sea turtles. Lactate levels were high, perhaps because the samples were taken from turtles coming ashore to lay eggs. Flatbacks are rarely found in waters deeper than 45 m. It is suggested that they have a respiratory physiology particularly suited to sustain prolonged shallow dives.

We investigated the capacity of two reptiles, an agamid lizard Pogona barbata and a chelid turtle Emydura signata, to compensate for the effects of temperature by making changes in their whole blood respiratory properties. This was accomplished by measuring the P50 (at 10, 20 and 30 °C), hematocrit (Hct), haemoglobin concentration ([Hb]) and mean cell haemoglobin concentration (MCHC) in field acclimatised and laboratory acclimated individuals. The acute effect of temperature on P50 in P. barbata, expressed as heat of oxygenation (ΔH), ranged from − 16.8 ± 1.84 to − 28.5 ± 2.73 kJ/mole. P50 of field acclimatised P. barbata increased significantly from early spring to summer at the test temperatures of 20°C (43.1 ± 1.2 to 48.8 ± 2.1 mmHg) and 30 °C (54.7 ± 1.2 to 65.2 ± 2.3 mmHg), but showed no acclimation under laboratory conditions. For E. signata, ΔH ranged from − 31.1 ± 6.32 to − 48.2 ± 3.59 kJ/mole. Field acclimatisation and laboratory acclimation of P50 did not occur. However, in E. signata, there was a significant increase in [Hb] and MCHC from early spring to summer in turtles collected from the wild (1.0 ± 0.1 to 1.7 ± 0.2 mmol/L and 4.0 ± 0.3 to 6.7 ± 0.7 mmol/L, respectively).

Many elements of mammalian and avian thermoregulatory mechanisms are present in reptiles, and the changes involved in the transition to endothermy are more quantitative than qualitative. Drawing on our experience with reptiles and echidnas, we comment on that transition and on current theories about how it occurred. The theories divide into two categories, depending on whether selection pressures operated directly or indirectly on mechanisms producing heat. Both categories of theories focus on explaining the evolution of homeothermic endothermy but ignore heterothermy. However, noting that hibernation and torpor are almost certainly plesiomorphic (=ancestral, primitive), and that heterothermy is very common among endotherms, we propose that homeothermic endothermy evolved via heterothermy, with the earliest protoendotherms being facultatively endothermic and retaining their ectothermic capacity for "constitutional eurythermy." Thus, unlike current models for the evolution of endothermy that assume that hibernation and torpor are specialisations arising from homeothermic ancestry, and therefore irrelevant, we consider that they are central. We note the sophistication of thermoregulatory behavior and control in reptiles, including precise control over conductance, and argue that brooding endothermy seen in some otherwise ectothermic Boidae suggests an incipient capacity for facultative endothermy in reptiles. We suggest that the earliest insulation in protoendotherms may have been internal, arising from redistribution of the fat bodies that are typical of reptiles. We note that short-beaked echidnas provide a useful living model of what an (advanced) protoendotherm may have been like. Echidnas have the advantages of endothermy, including the capacity for homeothermic endothermy during incubation, but are very relaxed in their thermoregulatory precision and minimise energetic costs by using ectothermy facultatively when entering short- or long-term torpor. They also have a substantial layer of internal dorsal insulation. We favor theories about the evolution of endothermy that invoke direct selection for the benefits conferred by warmth, such as expanding daily activity into the night, higher capacities for sustained activity, higher digestion rates, climatic range expansion, and, not unrelated, control over incubation temperature and the benefits for parental care. We present an indicative, stepwise schema in which observed patterns of body temperature are a consequence of selection pressures, the underlying mechanisms, and energy optimization, and in which homeothermy results when it is energetically desirable rather than as the logical endpoint.

Five species of antarctic fishes can be arranged in order of increasing anaerobic capacity of the white muscles for burst swimming: Rhigophila dearborni (Zoarcidae), icefish (Channichthyidae), Dissostichus mawsoni, Trematomus centronotus, and Pagothenia borchgrevinki (Nototheniidae). This order reflects increasing dependence on anaerobic work done during short bursts of speed during prey capture or predator avoidance. Buffer capacity (β) for white muscle was lower than that of behaviourally equivalent fish from lower latitudes and β is itself temperature-dependent.

We present some generalizations about the use of radio telemetry in physiological ecology, particularly to monitor body temperature and heart rate, drawn from work on free-ranging camels, echidnas, platypus, Tasmanian devils, quolls, crocodiles, bearded dragon lizards, goannas, freshwater turtles, and Queensland lungfish. We identify some potential pitfalls and describe some case studies, including the questions that drove the research and a brief review of some of the results.

We used implanted transmitters to track echidnas and record body temperatures year round. The resultant discovery of hibernation in these non-placental mammals (but not in their close relatives, platypus), sometimes in quite benign climates, poses questions about the origin of the ability to hibernate and the origin of endothermy itself. To help answer some of these, we developed a configuration for implantable transmitters to monitor heart rate in the field as an index of metabolic rate.

Short-beaked echidnas undergo both torpor and hibernation, expressed to different extents in different climates. We propose that when well fed animals hibernate in comparatively mild climates, with food available, they are using the winter cold as a resource and “putting themselves on ice” until the next breeding season. That is, echidnas are hibernating in mild climates for energy advantage, not from energetic necessity. We interpret the use of hibernation by echidnas in the more severe climates, where there is a food shortage, as a specialisation of a more general, ancestral capacity. There are also avian, marsupial and eutherian species in which torpor in mild climates appears to be practised for energetic advantage rather than from necessity. The similarity of patterns of hibernation in echidnas, mountain pigmy possums and arctic ground squirrels emphasises the likelihood that torpor and hibernation are plesiomorphic across all three Sub-classes of Mammalia. Attention is drawn to parallels between the daily/seasonal cycles in the body temperatures of torpidators/hibernators and those seen commonly in reptiles, and to the extent to which thermoregulatory mechanisms in reptiles foreshadow those in mammals and birds. The entry of mammals into torpor/hibernation may involve a reversal of the same physiological mechanisms which accompanied the evolution of endothermy from ectothermy, and echidnas may provide a useful model. A stepwise scenario for the evolution of endothermy is presented, with torpor/hibernation as a central theme. In presenting this scenario, we take care to distinguish between pattern and mechanism, recognising that the terms torpor and hibernation, like poikilothermy and homeothermy, are descriptive of patterns, not mechanisms, and that this limitation of the current terminology must be recognised.