Can birds do it too? Evidence for convergence in evaporative water loss regulation for birds and mammals.

Birds have many physiological characteristics that are convergent with mammals. In the light of recent evidence that mammals can maintain a constant insensible evaporative water loss (EWL) over a range of perturbing environmental conditions, we hypothesized that birds might also regulate insensible EWL, reflecting this convergence. We found that budgerigars (Melopsittacus undulatus) maintain EWL constant over a range of relative humidities at three ambient temperatures. EWL, expressed as a function of water vapour pressure deficit, differed from a physical model where the water vapour pressure deficit between the animal and the ambient air is the driver of evaporation, indicating physiological control of EWL. Regulating EWL avoids thermoregulatory impacts of varied evaporative heat loss; changes in relative humidity had no effect on body temperature, metabolic rate or thermal conductance. Our findings that a small bird can regulate EWL are evidence that this is a common feature of convergently endothermic birds and mammals, and may therefore be a fundamental characteristic of endothermy.

Reexamining Echidna Physiology: The Big Picture for Tachyglossus aculeatus acanthion.

The early divergence of monotremes and therian mammals has resulted in considerable interest in the comparative physiology of the short-beaked echidna (Tachyglossus aculeatus), the most common and widespread living monotreme. However, there are many and varied interpretations of its physiology, reflecting the many and varied studies, limitations and uncertainties of aspects of some previous studies, and potential differences between the various subspecies. Consequently, we thoroughly examine here the standardized physiology of the most widely distributed subspecies of short-beaked echidna (T. aculeatus acanthion) over a wide range of ambient temperatures to definitively assess its physiology in a comparative context. We conclude that the low and variable body temperature of the short-beaked echidna is physiologically "primitive," but it also reflects adaptation to its myrmecophagous niche. Other aspects of its physiology are more typically mammalian. A low metabolic rate reflects its low body temperature, and ventilatory variables are matched to accommodate a modest gas exchange requirement. Thermal conductance is typical for a mammal of equivalent mass. In contrast to previous studies, we demonstrate that short-beaked echidnas can enhance evaporative water loss above thermoneutrality, like other mammals, with a similar capacity for evaporative heat loss. Cooling of their nasal blood sinus with nasal mucous may contribute to this enhanced evaporative cooling. Their capacity to evaporatively cool explains how their distribution can include habitats where ambient temperature, even in shelters, exceeds their supposed critical thermal limit.

Environmental physiology of a small marsupial inhabiting arid floodplains.

Giles' planigale (Planigale gilesi) is among the smallest extant marsupials and inhabits deep soil cracks in arid floodplains. We examined whether its physiology shows specific adaptations to its extreme habitat. Metabolic rate, body temperature, evaporative water loss and thermal conductance were measured for eight planigales (average mass 9 g) exposed to four different ambient temperatures ranging from 10 degrees C to 32 degrees C. Water economy and respiratory variables were measured for the first time in this species. All of these standard physiological variables conformed to allometrically-predicted values for a marsupial. All variables were significantly affected by ambient temperature, except tidal volume and dry thermal conductance. Metabolic rate increased substantially at low ambient temperatures, as required to maintain a relatively constant body temperature of about 32-34 degrees C. This increased oxygen demand was accommodated by increased ventilation rather than increased oxygen extraction. Planigales had a comparatively high point of relative water economy of 19.1 degrees C, consistent with their small body size and arid habitat. Torpor reduced energy expenditure by 79% and evaporative water loss by 62%. Our study suggests that torpor use, along with behavioural adaptations, suffice for P. gilesi to live underground in arid habitats without further physiological adaptations.

Effect of sampling regime on estimation of basal metabolic rate and standard evaporative water loss using flow-through respirometry.

Strict criteria have been established for measurement of basal metabolic rate and standard evaporative water loss to ensure that data can be compared intra- and interspecifically. However, data-sampling regimes vary, from essentially continuous sampling to interrupted (switching) systems with data recorded periodically at more widely spaced intervals. Here we compare one continuous and three interrupted sampling regimes to determine whether sampling regime has a significant effect on estimation of basal metabolic rate or standard evaporative water loss. Compared to continuous 20-s sampling averaged over 20 min, sampling every 6 min and averaging over 60 min overestimated basal metabolic rate and evaporative water loss, sampling every 3 min and averaging over 21 min underestimated basal metabolic rate, and sampling every 12 min and averaging over 36 min showed no difference in estimates. Increasing the period over which the minimum mean was calculated significantly increased estimates of physiological variables. Reducing the frequency of sampling from 20 s to a longer interval of 3, 6, or 12 min underestimated basal metabolic rate but not evaporative water loss. This indicates that sampling frequency per se influences estimates of basal metabolic rate and that differences are not just an artifact of differences in the period over which the mean is calculated. Sampling regime can have a highly significant influence on estimation of standard physiological variables, although the actual differences between sampling regimes were generally small (usually <5%). Although continuous sampling is the preferred sampling regime for open-flow respirometry studies, if time and cost are prohibitive, then use of an appropriate switching system will result in smaller errors than measuring individuals continuously for shorter periods.

Effects of measurement duration on the determination of basal metabolic rate and evaporative water loss of small marsupials: how long is long enough?

We examined the time course for measurement of basal metabolic rate (BMR; measured as O(2) consumption and CO(2) production) and standard evaporative water loss (EWL) for six species of small marsupial to determine the minimum time required to achieve basal/standard values. There was a highly significant effect of measurement duration on measured physiological variables with values for O(2) consumption, CO(2) production, and EWL decreasing with time for all species. The time required to attain values statistically indistinguishable from minimal differed significantly between species, but in general O(2) consumption rate reached basal values after 4.3 h, CO(2) production after 4.5 h, and evaporative water loss after 5.2 h. For 16 BMR measurements of small marsupial species in the literature, with experimental duration provided, 10 were for less than 4 h, suggesting that their BMR values might be overestimates. For EWL, three of the four published values for small marsupials may be overestimates. It is clear that appropriate experimental duration is an important component of the measurement protocol for both BMR and standardized water loss, which needs to be rigorously observed in future studies.

Metabolic, ventilatory and hygric physiology of the chuditch (Dasyurus geoffroii; Marsupialia, Dasyuridae).

The chuditch is a large carnivorous dasyurid marsupial. Historically it had one of the widest geographical distributions of all marsupials, encompassing much of arid Australia, but it is now restricted to the mesic south-west of Western Australia. It is therefore of interest to determine if its physiology better reflects adaptation to its historically arid or present mesic habitat. The basic physiological parameters of the chuditch conform to other marsupials. Body mass of males (1385 g) was >400% of that predicted by phylogeny and this may be related to its carnivorous diet. Body temperature was 33.9 degrees C at ambient temperatures < or = thermoneutrality, with hyperthermia occurring above thermoneutrality. Basal metabolic rate was 0.361 mL O(2) g(-1) h(-1) at an ambient temperature of 31 degrees C. Metabolic rate increased below the thermoneutral zone by 0.038 mL O(2) g(-1) h(-1) degrees C(-1), and above the thermoneutral zone to 0.444+/-0.059 mL O(2) g(-1) h(-1) at 33.3 degrees C. Standard evaporative water loss was 0.498+/-0.071 mg g(-1) h(-1) at an ambient temperature of 26.0 degrees C, and increased at higher ambient temperatures due to panting and licking. Changes in wet thermal conductance largely reflected changes in evaporative heat loss, and dry thermal conductance increased at high ambient temperature due in part to posture change. Ventilatory parameters were consistent with metabolic demands in and below thermoneutrality, and suggested augmented evaporative heat loss above the thermoneutral zone. Chuditch had a high point of relative water economy of 22.6 degrees C, indicating favourable water economy at even moderate ambient temperatures, due to its low evaporative water loss rather than high metabolic water production. Chuditch were physiologically more similar to marsupials from arid rather than mesic habitats, better reflecting their historical distribution than their current geographical range.

Metabolic, ventilatory, and hygric physiology of the gracile mouse opossum (Gracilinanus agilis).

We present the first complete study of basic laboratory-measured physiological variables (metabolism, thermoregulation, evaporative water loss, and ventilation) for a South American marsupial, the gracile mouse opossum (Gracilinanus agilis). Body temperature (T(b)) was thermolabile below thermoneutrality (T(b) = 33.5 degrees C), but a substantial gradient between T(b) and ambient temperature (T(a)) was sustained even at T(a) = 12 degrees C (T(b) = 30.6 degrees C). Basal metabolic rate of 1.00 mL O2 g(-1) h(-1) at T(a) = 30 degrees C conformed to the general allometric relationship for marsupials, as did wet thermal conductance (5.7 mL O2 g(-1) h(-1) degrees C(-1)). Respiratory rate, tidal volume, and minute volume at thermoneutrality matched metabolic demand such that O2 extraction was 12.4%, and ventilation increased in proportion to metabolic rate at low T(a). Ventilatory accommodation of increased metabolic rate at low T(a) was by an increase in respiratory rate rather than by tidal volume or O2 extraction. Evaporative water loss at the lower limit of thermoneutrality conformed to that of other marsupials. Relative water economy was negative at thermoneutrality but positive below T(a) = 12 degrees C. Interestingly, the Neotropical gracile mouse opossums have a more positive water economy at low T(a) than an Australian arid-zone marsupial, perhaps reflecting seasonal variation in water availability for the mouse opossum. Torpor occurred at low T(a), with spontaneous arousal when T(b) > 20 degrees C. Torpor resulted in absolute energy and water savings but lower relative water economy. We found no evidence that gracile mouse opossums differ physiologically from other marsupials, despite their Neotropical distribution, sympatry with placental mammals, and long period of separation from Australian marsupials.

Allometry of evaporative water loss in marsupials: implications of the effect of ambient relative humidity on the physiology of brushtail possums (Trichosurus vulpecula).

To better understand the effects of ambient relative humidity (RH) on physiological variables and the implications of RH-correcting evaporative water loss (EWL) data for marsupials, we examined the effect of RH on EWL, body temperature (Tb), metabolic rate (MR) and thermal conductance (C) of the brushtail possum (Trichosurus vulpecula), a medium-sized marsupial. Correcting EWL data for 27 species of marsupial for water vapour pressure deficit (DeltaWVP) in the chamber during measurement significantly increased, rather than decreased, the variability of the allometric relationship for EWL. For the brushtail possum, both ambient temperature (Ta) and RH significantly affected EWL. At Ta=25 degrees C, EWL was independent of RH at "63% RH, but decreased linearly at higher RH values. At Ta=30 degrees C, EWL was significantly related to RH from 26% to 92% RH. There was a significant effect of Ta on Tb and dry thermal conductance (Cdry; higher at 30 degrees C), but no effect of RH. For MR and wet thermal conductance (Cwet) there was a significant effect of Ta (MR higher and Cwet lower at 25 degrees C), and RH at Ta=30 degrees C (MR higher and Cwet lower at the lowest RH) but not at 25 degrees C. Our results indicate that brushtail possums do not necessarily show the linear relationship between ambient RH and EWL expected for an endotherm, possibly because of behavioural modification of their immediate microclimate. This may account for the failure of WVP deficit correction to improve the allometric EWL relationship for marsupials. Chamber RH is an important environmental factor to be considered when measuring standard physiological variables such as MR and Cwet.

Environmental correlates of physiological variables in marsupials.

We analyzed body temperature (T(b)), basal metabolic rate (BMR), wet thermal conductance (C(wet)), and evaporative water loss (EWL) of marsupials by conventional and phylogenetically corrected regression. Allometric effects were substantial for BMR, C(wet), and EWL but not T(b). There was a strong phylogenetic signal for mass and all physiological traits. A significant phylogenetic signal remained for BMR, C(wet), and EWL even after accounting for the highly significant phylogenetic signal of mass. T(b), BMR, C(wet), and EWL allometric residuals were correlated with some diet, distribution, and climatic variables before and after correction for phylogeny. T(b) residuals were higher for marsupials from arid environments (high T(a) and more variable rainfall). The fossorial marsupial mole had a lower-than-expected T(b) residual. The allometric slope for BMR was 0.72-0.75. Residuals were consistently related to distribution aridity and rainfall variability, with species from arid and variable rainfall habitats having a low BMR, presumably to conserve energy in a low-productivity environment. The nectarivorous honey possum had a higher-than-expected BMR. For C(wet), the allometric slope was 0.55-0.62; residuals were related to diet, with folivores having low and insectivores high C(wet) residuals. The allometric slope for EWL was 0.68-0.73. EWL residuals were consistently correlated with rainfall variability, presumably facilitating maintenance of water balance during dry periods.

Numbats and aardwolves--how low is low? A re-affirmation of the need for statistical rigour in evaluating regression predictions.

Many comparative physiological studies aim to determine if a particular species differs from a prediction based on a linear allometric regression for other species. However, the judgment as to whether the species in question conforms to this allometric relationship is often not based on any formal statistical analysis. An appropriate statistical method is to compare the new species' value with the 95% confidence limits for predicting an additional datum from the relationship for the other species. We examine the basal metabolic rate (BMR) of the termitivorous numbat (Myrmecobius fasciatus) and aardwolf (Proteles cristatus) to demonstrate the use of the 95% prediction limits to determine statistically if they have a lower-than-expected BMR compared to related species. The numbat's BMR was 83.6% of expected from mass, but fell inside the 95% prediction limits for a further datum; a BMR < 72.5% of predicted was required to fall below the one-tail 95% prediction limits. The aardwolf had a BMR that was only 74.2% of predicted from the allometric equation, but it also fell well within the 95% prediction limits; a BMR of only 41.8% of predicted was necessary to fall below the one-tail 95% prediction limits. We conclude that a formal statistical approach is essential, although it is difficult to demonstrate that a single species statistically differs from a regression relationship for other species.

Water relations of the burrowing sandhill frog, Arenophryne rotunda (Myobatrachidae).

Arenophryne rotunda is a small (2-8 g) terrestrial frog that inhabits the coastal sand dunes of central Western Australia. While sand burrowing is a strategy employed by many frog species inhabiting Australia's semi-arid and arid zones, A. rotunda is unique among burrowing species because it lives independently of free water and can be found nocturnally active on the dune surface for relatively extended periods. Consequently, we examined the physiological factors that enable this unique frog to maintain water balance. A. rotunda was not found to have any special adaptation to reduce EWL (being equivalent to a free water surface) or rehydrate from water (having the lowest rehydration rate measured for 15 Western Australian frog species), but it was able to maintain water balance in sand of very low moisture (1-2%). Frogs excavated in the field were in dune sand of 4.4% moisture content, as a consequence of recent rain, which was more than adequate for these frogs to maintain water balance as reflected by their low plasma and urine osmotic concentrations. We suggest that in dry periods of the year, A. rotunda can achieve positive water balance by cutaneous water uptake by burrowing deeper into the substrate to where the percent water content is greater than 1.5%.

Significant decrease in the prevalence of Wuchereria bancrofti infection in anopheline mosquitoes following the addition of albendazole to annual, ivermectin-based, mass treatments in Nigeria.

A prospective entomological survey was conducted in four sentinel villages in central Nigeria from 1999-2002, to assess the impact of annual, single-dose, mass drug administrations (MDA), with a combination of ivermectin and albendazole, on the transmission of Wuchereria bancrofti. As they were also endemic for human onchocerciasis, the four villages had received annual MDA based on ivermectin alone for 7 years prior to the addition of albendazole. Resting Anophelines gambiae s. l., An. funestus and Culex species were collected from 92 sequentially sampled households and dissected. Mosquitoes harbouring any larval stage of W. bancrofti were classified as 'infected', and those containing the third-stage larvae of the parasite were classified as 'infective'. Over the 41-month observation period, 4407 mosquitoes were captured and dissected, of which 64% were An. gambiae s. l., 34% An. funestus, and 1% Culex species. The baseline data, from dissections performed before the addition of albendazole to the MDA, showed high prevalences of mosquito infection (8.9%) and infectivity (2.9%), despite apparently good treatment coverages during the years of annual ivermectin monotherapy. Only the anopheline mosquitoes were found to harbour W. bancrofti larvae. After the third round of MDA with the ivermectin-albendazole combination, statistically significant decreases in the prevalences of mosquito infection (down to 0.6%) and infectivity (down to 0.4%) were observed (P<0.0001 for each). The combination of albendazole and ivermectin appears to be superior to ivermectin alone for reducing the frequency of W. bancrofti infection in mosquitoes.

Termite digestibility and water and energy contents determine the water economy index of numbats (Myrmecobius fasciatus) and other myrmecophages.

Digestibility by captive numbats for termites was determined by feeding trials to be 81%+/-1.2% for Coptotermes sp. and 64%+/-3.3% for Nasutitermes sp. Water, ash, and energy content of both the Coptotermes (0.96+/-0.099 mg(dry mass) individual(-1), 78.0%+/-0.36% water, 5.8%+/-0.31% ash, 23.1+/-0.19 kJ g-1dry total energy) and Nasutitermes (0.91+/-0.046 mg(dry mass) individual(-1), 76.7%+/-3.09% water, 7.5%+/-1.10% ash, 22.7+/-0.36 kJ g-1dry total energy) were similar to values measured previously for other termites and for ants and insects in general. Numbats have a slow passage time for termites (20-30 h), presumably to enhance the digestion of termites. The water economy index (WEI) was 0.2 for captive numbats feeding on Coptotermes and 0.25 for Nasutitermes, whereas the WEI measured for wild, free-living numbats was 0.29, which corresponds to a digestibility of 58%. The WEI of a myrmecophage diet is determined by the energy and water contents and digestibilities of termites and ants, in the absence of drinking. The WEI for numbats, and other termitivorous mammals as well as reptiles, is higher than would be expected for an animal-based diet because of their relatively low digestibility (58%-81%) for termites. A high WEI preadapts myrmecophages to survival in arid environments without having to drink.

Spermatogenesis and plasma testosterone levels in Western Australian burrowing desert frogs, Cyclorana platycephala, Cyclorana maini, and Neobatrachus sutor, during aestivation.

Changes in testis size, histological status, and plasma levels of testosterone were monitored for males of three species of Western Australian desert frogs, Cyclorana maini, Cyclorana platycephala, and Neobatrachus sutor during aestivation. The frogs were induced to burrow and form cocoons soon after their capture and then disinterred at intervals in order to monitor changes in reproductive activity of the testes. All stages of spermatogenesis were evident in active frogs, which were collected a few days following rain from breeding choruses. Relative testis mass declined gradually in all species during the first 7 months of aestivation and then increased significantly at 16-19 months in the two species for which extended data were available (C. maini and N. sutor). A decrease in the number of sperm bundles 2-4 months after cocooning was associated with an initial increase in the number of free spermatazoa in all three species, which then returned to the levels seen in active animals after 7 months. Increases in the number of primary and secondary spermatogonia were most evident in C. platycephala after 4-7 months of aestivation, but early stages of spermatocytogenesis were evident in all species after 7 months of aestivation, especially in individuals that contained neither sperm bundles nor mature spermatazoa. Changes in plasma testosterone levels correlated significantly with variations in the diameter of the seminiferous tubules and the GSI, suggesting that this hormone plays a major role in controlling testicular recrudescence in aestivating, cocooned, desert frogs. Data from this study show that, in the absence of any external cues, testicular recrudescence is evident after approximately one year of aestivation in desert frogs which prepares them to breed again, once rain falls.

Ventilatory physiology of the numbat (Myrmecobius fasciatus).

This study examines the ventilatory physiology of the numbat (Myrmecobius fasciatus), a small to medium-sized (550 g) termitivorous marsupial. Ventilatory parameters at thermoneutrality reflect the slightly low (83% of predicted) basal metabolic rate of the numbat, with ventilation frequency (fR; 30.6+/-3.65 breaths min(-1)), tidal volume [VT; 6.0+/-0.66 ml at body temperature and pressure, saturated (BTPS)] and consequently minute volume (VI; 117.7+/-15.22 ml min(-1); BTPS) all being 80-87% of that expected for a marsupial of similar body mass. Oxygen extraction was 27.7+/-1.37% in the thermoneutral zone. As is typical of marsupials, numbats accommodated increased oxygen consumption rates at ambient temperatures (Ta) below the thermoneutral zone by increasing minute volume (up to 411.2+/-43.98 ml min(-1); BTPS at Ta=10 degrees C) rather than oxygen extraction. Minute volume at 10 degrees C increased more by changes in ventilation frequency (up to 45.5+/-4.85 breaths min(-1)) than tidal volume (9.4+/-1.03 ml, BTPS), as is also typical for a small-medium sized marsupial.

Field metabolic rate and water turnover of the numbat (Myrmecobius fasciatus).

The numbat (Myrmecobius fasciatus) is a diurnal and exclusively termitivorous marsupial. This study examines interrelationships between diet, metabolic rate and water turnover for wild, free-living numbats. The numbats (488+/-20.8 g) remained in mass balance during the study. Their basal metabolic rate (BMR) was 3.6 l CO(2) day(-1), while their field metabolic rate (FMR) was 10.8+/-1.22 l CO(2) day(-1) (269+/-30.5 kJ day(-1)). The ratio FMR/BMR was 3+/-0.3 for numbats. We suggest that the most accurate way to predict the FMR of marsupials is from the regression log FMR=0.852 log BMR+0.767; ( r(2)=0.97). The FMR of the numbat was lower than, but not significantly different from, that of a generalised marsupial, both before (76%) and after (62-69%) correction for the significant effect of phylogeny on FMR. However the numbat's FMR is more comparable with that of other arid-habitat Australia marsupials (98-135%), for which the regression relating mass and FMR is significantly lower than for nonarid-habitat marsupials, independent of phylogeny. The field water turnover rate (FWTR) of free-living numbats (84.1 ml H(2)O day(-1)) was highly correlated with FMR, and was typical (89-98%) of that for an arid-habitat marsupial after phylogenetic correction. The higher than expected water economy index for the numbat (FWTR/FMR=0.3+/-0.03) suggests that either the numbats were drinking during the study, the water content of their diet was high, or the digestibility of their termite diet was low. Habitat and phylogenetic influences on BMR and FMR appear to have pre-adapted the numbat to a low-energy termitivorous niche.

Biophysical properties of the pelt of a diurnal marsupial, the numbat (Myrmecobius fasciatus), and its role in thermoregulation.

Numbats are unusual marsupials in being exclusively diurnal and termitivorous. They have a sparse (1921 hairs cm(-2)) and shallow (1.19 mm) pelt compared with other marsupials. Coat reflectivity is low (19%) for numbats compared with nocturnal marsupials, but absorptivity is similar to that of diurnal North American ground squirrels (72%), indicating that the coat of the numbat may be adapted for acquisition of solar heat. Numbat coat thermal resistance decreases significantly with wind speed from 45.9 s m(-1) (at 0.5 m s(-1)) to 29.8 s m(-1) (at 3 m s(-1)). Erecting the fur significantly increases pelt depth (6.5 mm) and coat resistance (79.2-64.2 s m(-1)) at wind speeds between 0.5 m s(-1) and 3 m s(-1). Numbat coat resistance is much lower than that of other marsupials, and wind speed has a greater influence on coat resistance for numbats than for other mammals, reflecting the low pelt density and thickness. Solar heat gain by numbats through the pelt to the level of the skin (60-63%) is similar to the highest value measured for any mammal. However the numbat's high solar heat gain is not associated with the same degree of reduction in coat resistance as seen for other mammals, suggesting that its pelt has structural and spectral characteristics that enhance both solar heat acquisition and endogenous heat conservation. Maximum solar heat gain is estimated to be 0.5-3.6 times resting metabolic heat production for the numbat at ambient temperatures of 15-32.5 degrees C, so radiative heat gain is probably an important aspect of thermoregulation for wild numbats.

Thermoregulatory physiology of the Crested Pigeon Ocyphaps lophotes and the Brush Bronzewing Phaps elegans.

The metabolic physiology of the Crested Pigeon (Ocyphaps lophotes) and the Brush Bronzewing (Phaps elegans) is generally similar to that expected for birds of their size, but the Crested Pigeon has a number of characteristics which would aid survival in hot and dry regions. Body temperature increased similarly for the Crested Pigeon (from 38.8 degrees C to 41.5 degrees C) and the Brush Bronzewing (39.3 degrees C to 41.4 degrees C) over ambient temperatures (T(a)s) from 10 degrees C to 35 degrees C. Both species became hyperthermic (body temperature, T(b)>42 degrees C) at T(a)=45 degrees C. Basal metabolic rate of the Crested Pigeon (0.65 ml O(2) g(-1) h(-1) at 40 degrees C) was approximately 71% of that predicted for a columbid bird, while BMR of the Brush Bronzewing (0.87 ml O(2) g(-1) h(-1) at 20 degrees C to 40 degrees C) was approximately 102% of predicted. Total evaporative water loss increased exponentially with T(a) for both species, from <1 mg H(2)O g(-1) h(-1) at 10 degrees C to >12 mg H(2)O g(-1) h(-1) at 45 degrees C. It was similar and low for both species at T(a)<30 degrees C, but was higher for the Brush Bronzewing than the Crested Pigeon at T(a)>30 degrees C. Ventilatory minute volume matched oxygen consumption, such that oxygen extraction efficiency did not change with T(a) and was similar for both species (approximately 20%). Expired air temperature was considerably lower than T(b) for both species at T(a)<35 degrees C, potentially reducing respiratory water loss by approximately 65% at T(a)=10 degrees C to approximately 30% at T(a)=35 degrees C. Cutaneous evaporative cooling was significant for both species, with skin resistance decreasing as T(a) increased. The Crested Pigeon had a lower skin resistance than the Brush Bronzewing at T(a)=45 degrees C. The Brush Bronzewing had apparently reached its maximum cutaneous water loss at 30 degrees C and relied on panting to cool at higher T(a).

Metabolic physiology of the numbat (Myrmecobius fasciatus).

The numbat (Myrmecobius fasciatus) is unique amongst marsupials as it is exclusively diurnal, feeds only on termites and is semi-fossorial. This study examines the thermal and metabolic physiology of the numbat to determine if its physiology reflects its phylogeny, diet and semi-fossorial habit. Numbats (mean adult body mass 552 g) were able to regulate body temperature at ambient temperatures of 15-30 degrees C, with a body temperature at thermoneutrality (30 degrees C) of 34.1 degrees C. The thermoneutral body temperature was not significantly different from that predicted for an equivalent-sized marsupial. Basal metabolic rate, measured at 30 degrees C, was 0.389 +/- 0.025 ml O(2) g(-1) h(-1), and was slightly but not significantly lower at 82.5% of that predicted for a typical marsupial of equivalent body mass. Metabolic rate increased with decreasing ambient temperatures below 30 degrees C. Patterns of metabolic cycling observed for completely inactive numbats at ambient temperatures below 30 degrees C are likely to be related to sleep phase. Wet thermal conductance of 1.94 J g(-1) h(-1) degrees C(-1) (at 30 degrees C) was 131% of that predicted for a marsupial. Evaporative water loss of the numbat remained constant below the thermoneutral zone (<30 degrees C) at approximately 0.6 ml g(-1) h(-1), only 47.4% of that predicted for a marsupial. It increased to 1.01 +/- 0.16 ml g(-1) h(-1) at an ambient temperature of 32.5 degrees C. The thermal and metabolic physiology of the numbat is generally similar to that expected for other marsupials, and is also comparable to that of termitivorous placental mammals. Thus the reduction in body temperature and basal metabolic rate of placental termitivores is a "marsupial-like" low energy turnover physiology, and the numbat being a marsupial already has an appropriate physiology to survive exclusively on a low energy diet of termites.

Water content, body weight and acid mucopolysaccharides, hyaluronidase and beta-glucuronidase in response to aestivation in Australian desert frogs.

This study investigates the effects of aestivation on body water content, body mass, acid mucopolysaccharide (AMPS) and some of its degrading enzymes in different tissues for some Australian desert frogs. The AMPS component of the liver, kidney, skin and cocoon alter during aestivation to help retain water, which is unchanged in most tissues of all frog species, and to protect the frogs from desiccation during extended periods of aestivation. Hepatic AMPS was unaltered in Cyclorana maini, C. platycephala and Neobatrachus sutor but increased significantly after 2 months of aestivation in C. australis. The level of AMPS in the kidney was elevated in all four frog species after 5 months of aestivation. Skin AMPS content in the skin of awake frogs decreases with aestivation period and increases in the cocoon. AMPS in the cocoon probably works as a cement between the cocoons' layers and its physical presence presumably contributes to preventing water flux. Changes in AMPS content in different tissues were accompanied by significant changes in both hyaluronidase and beta-glucuronidase activities, which play an important role in AMPS metabolism. Alcian blue staining of control and digested skin of C. australis and C. platycephala with testicular hyaluronidase indicated the presence of AMPS, concentrated in a thin layer (called ground substance, GS) located between stratum compactum and stratum spongiosum, and acid mucin concentrated in the mucous glands and in a 'tubular' structure which could be observed in the epidermal layer. Hyaluronidase digestion of the cocoon slightly changed the Alcian Blue colour, suggesting the presence of a large amount of acid mucin similar to that found in the skin mucous gland. The results of this study present data for the redistribution of AMPS, which may help in reducing water loss across the cocoon and reabsorption of water in the kidney during aestivation.