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.

Gross renal morphology of the numbat (Myrmecobius fasciatus) (Marsupialia:Myrmecobiidae)

There is a strong correlation between the structure of the mammalian kidney and its urinary concentrating ability. We examine here the kidney of an endangered termitivorous marsupial (Myrmecobius fasciatus) and use the measured kidney morphometrics to calculate maximal urinary concentration. The relative medullary area (1.34) of the kidney of M. fasciatus is typical of other dasyuromorph marsupials, as is its predicted maximal urinary concentration of 3617 mOsm kg–1 H2O, despite its historically semiarid/arid distribution. The termitivorous diet of M. fasciatus presumably provides it with sufficient water to limit selection for a high urinary concentrating capacity.

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 (ΔWVP) 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°C, EWL was independent of RH at≤63% RH, but decreased linearly at higher RH values. At Ta=30°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°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°C), and RH at Ta=30°C (MR higher and Cwet lower at the lowest RH) but not at 25°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.

Diet and foraging behaviour of the semi-aquatic Varanus mertensi (Reptilia:Varanidae)

We report on the aquatic and terrestrial foraging behaviour and diet of the semi-aquatic Varanus mertensi. Foraging behaviour of V. mertensi is similar to that of other large terrestrial varanids: slow, methodical forwards movement with the head swaying from side to side with regular tongue flicks. Both olfactory and visual cues are used to detect prey. Foraging in the water is remarkably similar to that in the terrestrial environment, with this species using both visual and olfactory cues. Like other varanids, this species is able to use previous experiences to maximise its chance of locating prey. V. mertensi consume a large number of freshwater crabs (Holthuisana sp.) and a variety of small invertebrate and vertebrate prey across their distribution. Dietary differences across geographic regions are minor. Its diet is sufficiently catholic to enable it to adapt to seasonal and spatial differences in prey availability, one reason for its widespread distribution in the wet–dry tropics of Australia. Stomach contents differ from those of scats, with soft-bodied prey items being absent from scat samples.

Physiological significance of the microclimate in night refuges of the numbat Myrmecobius fasciatus

Numbats (Myrmecobius fasciatus) seek overnight refuge in hollow logs, tree hollows and burrows, which provide protection from predators. Occupied night refuges were on average 5�C warmer than ambient temperature, which would result in considerable energy savings (35 kJ over 12 h). Use of a nest within the refuge reduced calculated energy expenditure by a further 55 kJ over 12 h. Mean nightly temperature didn?t differ with refuge type, but the nightly pattern of refuge temperature did. Burrows had higher insulation than logs or tree hollows, and had more constant night temperatures and higher minimum temperatures. Season had a significant influence on refuge temperature, with lower temperatures in winter than in other seasons for all refuge types. The gas composition of occupied night refuges was different to ambient, with refuge air differing in O2 content by a maximum of 2.3%, and CO2 by no more than 3.0% from ambient levels. The relative humidity in M. fasciatus refuges was extremely variable (23- 100%), but was generally lower than ambient relative humidity. The overnight refuges of M. fasciatus (hollow logs, tree hollows and burrows) significantly buffer thermal conditions without major effects on the gaseous or hygric environment.

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.

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.

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.

Influence of season and weather on activity patterns of the numbat (Myrmecobius fasciatus) in captivity

To separate the influence of weather from predation pressure and food availability, and to aid in the interpretation of activity data for wild numbats, we examined the influence of season and weather on the activity of captive numbats. Unlike other Australian marsupials, numbats are exclusively diurnal, being active for an average of 21.2% of the 24 h day. However, in the present study, activity duration varied seasonally, with numbats being active for longer periods in summer (39–65% of the available daylight) than winter (17–59%). During winter, captive numbats were active for shorter periods than wild numbats (presumably because captive numbats don't have to forage for food); however, they did not cease activity in the middle of the day during summer (suggesting that the inactivity of wild numbats at midday during summer is a response to food availability rather than a thermoregulatory response). Captive numbats were more active in summer than in winter, which may reflect their summer breeding season. Environmental conditions significantly affected daily activity, with low levels of activity recorded on days of low light intensity and high relative humidity. The majority of numbat activity occurred at ambient temperatures below thermoneutrality (<30°C). The associated costs of thermoregulation for active numbats were calculated, from activity time, to be higher in winter (0.586 mL O2 g–1 h–1) than in summer (0.274 mL O2�g–1�h–1).

Are day-active small mammals rare and small birds abundant in Australian desert environments because small mammals are inferior thermoregulators?

Small desert birds are typically diurnal and highly mobile (hence conspicuous) whereas small non-volant mammals are generally nocturnal and less mobile (hence inconspicuous). Birds are more mobile than terrestrial mammals on a local and geographic scale, and most desert birds are not endemic but simply move to avoid the extremes of desert conditions. Many small desert mammals are relatively sedentary and regularly use physiological adjustments to cope with their desert environment (e.g., aestivation or hibernation). It seems likely that prey activity patterns and reduced conspicuousness to predators have reinforced nocturnality in small desert mammals. Differences such as nocturnality and mobility simply reflect differing life-history traits of birds and mammals rather than being a direct result of their differences in physiological capacity for tolerating daytime desert conditions.

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.

Metabolic ecology of cockatoos in the south-west of Western Australia

This study examined the metabolic ecology of six cockatoo taxa endemic to the south-west of Western Australia. As the availability of food is one factor that may influence the abundance and distribution of these cockatoos, we document here their baseline energy requirements and feeding patterns. Evaporative waterloss was also measured as this may correlate with the aridity of the species’ environment. Basal metabolic rate was significantly lower at 0.62 ± 0.13 mL O2 g–1 h–1 for the inland red-tailed black cockatoo than 1.11 ± 0.16 mL O2 g–1 h–1 for the forest red-tailed black cockatoo, but there was no significant difference in metabolic rate between the two white-tailed black cockatoos (0.86 ± 0.18 for Carnaby’s and 0.81 ± 0.11 mL O2 g–1 h–1 for Baudin’s) or the two corellas (0.95 ± 0.12 for Butler’s and 0.70 ± 0.04 mL O2 g–1 h–1 for Muir’s). There were no significant differences between the two white-tailed black cockatoos, and between the two corellas, with respect to evaporative water loss. The inland red-tailed black cockatoo had a significantly lower rate of evaporative water loss (0.44 ± 0.07 mg g–1 h–1) than the forest red-tailed black cockatoo (0.70 ± 0.06 mg g–1 h–1), which is presumably an adaptation to its more arid habitat. The total energy content of assorted native and introduced food items that form significant proportions of the diets for these cockatoos varied from only 0.17 kJ for a 9-mg Emex australis seed to 63.9 kJ for a 3-g Banksia attenuata nut. The energy content of each food item and the estimated daily energy requirements of the cockatoos enabled the calculation of the numbers of nuts/cones/seeds required by each species for a day, which ranged from 11 B. attenuata nuts for a Carnaby’s cockatoo to 3592 Persoonia longifolia seeds for a forest red-tailed black cockatoo.

Re-evaluation of the allometry of wet thermal conductance for birds

Wet thermal conductance is an important thermoregulatory parameter for birds and mammals. It is generally calculated as C(wet) (ml O2 g(-1) h(-1) degrees C(-1)) = VO2/(T(b)-T(a)), where VO2 is metabolic rate measured in ml O2 g(-1) h(-1), T(b) is body and T(a) is ambient temperature measured in degrees C. Minimum C(wet) is measured at T(a) at or below the lower critical temperature (T(lc)) of the thermoneutral zone, and is strongly influenced by time of day (rest or activity phase) and body mass [J. Aschoff, Comp. Biochem. Physiol. 69A (1981) 611]. Allometric analyses indicate differences in C(wet) for passerine and non-passerine birds, in their rest and active phases (Aschoff, 1981). The allometric slope for non-passerine rest-phase (-0.583) is lower than that for non-passerine active-phase (-0.484), and passerine rest-phase (-0.461) and active-phase (-0.463), although none of these slopes are significantly different. This different-sloped relationship for non-passerine rest-phase C(wet) extrapolates to lower-than-expected values at high body mass, and so this allometric relationship may be inappropriate for predictive purposes. Consequently, we have reanalysed Aschoff's (1981) data, as well as more recent compilations, to determine a more useful allometric relationship for C(wet) of non-passerine rest-phase birds. Re-analyses of minimum thermal conductance data from Drent and Stonehouse [Comp. Biochem. Physiol. 40A (1971) 689], Aschoff (1981) and Gavrilov and Dolnik [Acta XVIII Congressus Internationalis Ornithologici Moscow (1982) 421] indicate that the most appropriate regressions for predicting C(wet) (ml O2 g(-1) h(-1) degrees C(-1)) of birds from body mass (M; g) are the pooled regressions for non-passerine and passerine birds, in the active (alpha) and resting (rho) phases, using data tabulated by Aschoff (1981): alpha, C(wet)=0.994M(-0.509); rho, C(wet)=0.702M(-0.519). C(wet) is approximately 40% higher in the active phase than the rest phase. Regressions of various data sets for C(wet) of birds and mammals indicate a similar slope of approximately -0.5 for the allometric relationship, but significantly higher elevations for mammals compared to birds. The approximately 50% higher C(wet) for mammals than birds indicates a better physical insulation for birds than mammals of the same body mass. The general scaling of C(wet) with M(-0.5) indicates that (T(b)-T(lc)) should scale with M(0.22), if mass-specific metabolic rate scales with M(-0.28) [Reynolds and Lee, Am. Nat. 147 (1996) 735]. The observed scaling for (T(b)-T(lc)) of M(0.183) (calculated from Gavrilov and Dolnik, 1985) is consistent with this expectation.

Design, calibration and calculation for flow-through respirometry systems

Flow-through respirometry systems that measure oxygen consumption (VO2), carbon dioxide production (VCO2) and evaporative water loss (EWL) require the accurate calibration of the flow meter and three separate analysers (O2, CO2 and H2O vapour). Correct measurement of VO2, VCO2 and EWL depends on the incurrent air flow (VI) and its condition (e.g. dry, CO2-free), and the excurrent air flow (VE) and its condition (e.g. dry, CO2-free), which can differ in different parts of the excurrent circuit. Usually either VI or VE is measured and the other is calculated from the gas composition. I describe here a procedure for precise calibration of CO2 and H2O analysers in a flow-through respirometry system by reference to a calibrated O2 analyser, using a small gas flame. Generic equations are derived for calculation of VO2, VO2 and EWL with a variety of configurations for a flow-through respirometry system. Procedures for selection of data from continuous records of VO2, VCO2 and EWL for calculation of minimal (basal or standard) values are briefly described. Finally, the importance of the correct order of data treatment prior to calculation is described.

Dracunculiasis eradication: delayed, not denied

By the end of 1998, Asia was free of dracunculiasis (Guinea worm disease), with Pakistan, India, and Yemen having interrupted transmission in 1993, 1996, and 1997, respectively. Transmission of the disease was also interrupted in Cameroon and Senegal during 1997. Chad reported only 3 cases during 1998. Dracunculiasis is now confined to only 13 countries in Africa. The overall number of cases has been reduced by more than 97% from the 3.2 million cases estimated to have occurred in 1986 to 78,557 cases reported in 1998. Because the civil war in Sudan remains the major impediment to eradication of dracunculiasis, the interim goal is to stop all transmission outside that country by the end of 2000. The most important operational need now is for national programs to improve the frequency and quality of supervision of village-based health workers in order to enhance the sensitivity of surveillance and effectiveness of case containment.

Metabolic physiology of the north-western marsupial mole, Notoryctes caurinus (Marsupialia : Notoryctidae)

We studied the thermal and metabolic physiology of a single specimen of the north-western marsupial mole, Notoryctes caurinus, an almost completely fossorial Australian marsupial, and compared it with the morphologically convergent Namib desert golden mole, Eremitalpa granti namibensis. This was the first study of any aspect of the physiology of this rare marsupial. Mean body mass of the marsupial mole was 34 g. Body temperature (Tb) was low and labile, ranging from 22.7 to 30.8˚C over a range of ambient temperature (Ta) from 15 to 30˚C. The highest Tb of 30.8˚C was significantly lower than expected for a marsupial of this body mass. Metabolic rate varied with Ta in an attenuated fashion for an endotherm, because of the labile Tb. Basal metabolic rate (BMR) was 0.63 mL O2 g–1 h–1, at a Ta of 30˚C. This was lower than expected for a 34-g marsupial, but was not different from expected for a marsupial when corrected to a Tb of 35˚C (0.94 mL O2 g–1 h–1). Evaporative water loss increased from 0.8 mg g–1 h–1 at 15˚C to 3.7 at 30˚C. Wet thermal conductance was 0.2 mL O2 g–1 h–1 ˚C–1 at 15˚C and 0.6 at 25˚C; these values were higher than expected for a marsupial. The net metabolic cost of transport (NCOT) for running (0.0022 mL O2 g–1 m–1 at a mean velocity of 484 m h–1) was similar to expected values for walking and running mammals. The NCOT for sand-swimming (0.124 mL O2 g–1 m–1 at a mean velocity of 7.6 m h–1) was substantially higher, and at a much lower velocity than for running, but was similar to NCOT for sand-swimming by the Namib golden mole. We conclude that the marsupial mole differs in some aspects of thermal and metabolic physiology from other marsupials, most likely reflecting its almost completely fossorial existence.

Metabolism and evaporative water loss of Western Australian geckos (Reptilia : Sauria : Gekkonomorpha)

Resting metabolic rate (RMR) and evaporative water loss (EWL) were measured, and resistance (R) to evaporative water loss and water use index (WUI = EWL/RMR) were calculated, for 22 species of Western Australian gecko. For all available gecko data, body mass and temperature explained 85% of the variability in RMR (=14.5 mass0.833 100.0398 Ta µL h–1), and 70% of the variability in EWL (=0.126 mass0.539 100.049 Ta mg h–1 ). For Western Australian geckos, RMR and EWL were significantly influenced by body mass, using conventional regression and phylogenetic analyses. Resistance to evaporative water loss (R) was not significantly affected by body mass. Water use index was inversely related to body mass: WUI = 21.9 M–0.344 mg mL O2–1. There were significant differences between species for R and for standardised residuals of RMR, EWL and WUI. R was not correlated with phylogeny, and was significantly higher (P = 0.020) for saxicolous geckos (1467 s cm-1) than terrestrial geckos (797 s cm–1); arboreal geckos had an intermediate R (977 s cm–1). Species that ate termites had lower standardised linear regression residuals (P = 0.003) for RMR than did species that ate more general diets. Standardised residuals for EWL were almost significantly related to microhabitat (P = 0.053). Standardised residuals for WUI were significantly related to microhabitat (P = 0.016); saxicolous species had lower WUI than terrestrial species. Standardised linear regression residuals of the residuals from autoregression (which should be independent of both mass and phylogeny effects) still significantly correlated RMR and diet, but not EWL or WUI with microhabitat.

Standard metabolic rates of three nectarivorous meliphagid passerine birds

Standard metabolic rate (VO2 STD) was determined for three species of passerine bird from the family Meliphagidae to investigate the possible effect of nectarivory on standard metabolic rate in this family. The three species that we investigated did not show a significant departure from allometric predictions of standard metabolic rate for passerine species. Disparities between standard metabolic rate for meliphagids in the present study and previous data appear to reflect methodological differences, and no general allometric relationship is apparent for meliphagids at present. In meliphagids, nectarivory per se is not an important correlate with standard metabolic rate. Data from additional meliphagid species, collected under standardised conditions, are required to confirm the generality of the findings of the present study, that nectarivorous meliphagids have a standard metabolic rate typical of passerine birds.

Urea: diverse functions of a 'waste' product

1. The urea cycle is essentially the simultaneous operation of two linear pathways, both primitive and widespread among animals; one is for arginine synthesis and the other is for arginine degradation to ornithine and urea. 2. All animals may have the genetic capacity to express a urea cycle and many diverse groups of animals, from flatworms to mammals, have a functional urea cycle. 3. Evolutionary changes in vertebrates of carbamylphosphate synthetase (CPS) are directed from glutamine-dependent (CPSIII) towards NH3-dependent (CPSI) ureagenesis. Invertebrates, cartilagenous fish and the coelacanth have CPSIII (i.e. glutamine-dependent), whereas lungfish, amphibians and amniote vertebrates have CPSI; the teleost Heteropneustes has CPSI-like activity. That the coelacanth has CPSIII and Heteropneustes has 'CPSI' suggests that the form of CPS may by physiologically related (CPSIII in a balancing solute role and CPSI in a terrestrial, air-breathing excretion role) rather than being phylogenetically constrained. 4. Urea is a major balancing osmolyte in marine cartilagenous fish, the coelacanth and a few amphibians and some aestivating terrestrial amphibians. It is a storage osmolyte in cocoon-forming aestivating lungfish and amphibians. 5. Urea contributes towards positive buoyancy in marine cartilagenous fish. 6. Urea functions for non-toxic N transport in ruminant and pseudoruminant mammals. 7. Urea is a major solute in the mammalian (but not avian) kidney, contributing to a renal medullary osmotic gradient; it is substantially reabsorbed by mammalian nephrons. 8. Urea is used as a preferred nitrogenous waste compared with ammonia at high ambient pNH3 or pH, with water restriction, or air breathing. 9. Urea synthesis maintains acid-base balance by the 1:1 stoichiometry of removal of HCO3- and NH4+.

The role of protein synthesis during metabolic depression in the Australian desert frog Neobatrachus centralis

Little is known about the role of energy consuming processes during metabolic depression. We have shown that aestivation in the Australian desert frog Neobatrachus centralis is accompanied by an in vivo metabolic depression of 77%. Using an in vitro liver slice preparation, we have measured an in vitro metabolic depression in liver of 55%, with a concomitant 67% decrease in the rate of protein synthesis. The decrease in protein synthesis accounts for 52% of the metabolic depression of the tissue, but only 4.9% of the metabolic depression of the whole animal. No in vitro metabolic depression or decrease in protein synthesis during aestivation was measured in muscle, but a decrease in the low rate of protein synthesis in muscle in vivo could not, in any case, account for more than 3% of the metabolic depression of the whole animal. The liver, although not a quantitatively important tissue in terms of metabolic depression in vivo, offers the opportunity to characterise the regulation of protein synthesis in a system in which metabolic depression is not confounded by changes in ambient temperature and PO2.

Oxygen consumption, carbon dioxide excretion and respiratory quotient of larval lampreys (Mordacia mordax) in air

The standard rates of O2 consumption of larval Mordacia mordax (weight range 1.3-2.3 g), after these ammocetes had been in humidified air for 18 hr, were 26.8, 46.3 and 71.2 microL x g(-1) x hr(-1) at 10, 15 and 20 degrees C, respectively. The corresponding rates of CO2 excretion were 20.7, 35.6 and 54.1 microL x g(-1) x hr(-1). The RQs at the three temperatures were essentially identical (0.76 or 0.77) and similar to that of adults of the lamprey Geotria australis in air at 15 degrees C. The above RQs for ammocoetes, which are probably similar to those that would be recorded in water, are consistent with the view that the aerobic respiration of these animals relies predominantly on lipid as an energy source, but that some energy is derived from carbohydrate and/or protein. The RQs for larval and adult lampreys in air lie well within the range recorded for amphibious fishes in air.

Protein synthesis in the liver of Bufo marinus: cost and contribution to oxygen consumption

While many estimates of the contribution of protein synthesis to metabolic rate exist for a variety of animals, most rely on theoretical costs of protein synthesis. The limitations of this approach are that theoretical costs depend upon variable estimates of ATP cost per peptide bond. In addition, they do not take into account the fact that there are protein-specific pre- and post-translational costs. By inhibiting, protein synthesis with cycloheximide and measuring the resultant decrease in oxygen consumption, we have measured the actual cost of protein synthesis and its contribution to metabolic rate in an in vitro system of tissue slices from Bufo marinus. Such measurements exist for endotherms, but there are few such measurements for ectotherms, and none have been done previously for amphibians. The cost of protein synthesis in liver slices from B. marinus was 7.32+/-1.19 mmol O2 x g(protein)(-1) (x +/- SE, n = 48) and protein synthesis accounted for 12% of the total metabolic rate of this tissue. This cost is comparable to values measured for other ectotherms although the contribution of protein synthesis to metabolic rate is at the lower end of the range of estimates for other ectotherms.

Standard and maximal metabolic rates of goannas (Squamata:Varanidae)

Standard metabolic rate and maximal metabolic rate during forced exercise are examined for nine species of goanna (genus Varanus), with body mass varying from 10 to 3,750 g. At 35 degrees C, the common pooled mass exponent for standard metabolic rate is 0.97 and at 25 degrees C it is 0.89, with considerable variation between species (0.43-1.20). Standard metabolic rate at 35 degrees C scales interspecifically with body mass0.92 and at 25 degrees C with body mass0.87. The Q10 for standard metabolic rate is approximately 2.5 between 25 degrees and 35 degrees C. At 35 degrees C, maximal metabolic rate scales intraspecifically with body mass0.79 and scales interspecifically with body mass0.72. Factorial metabolic scope ranges from nine for the larger species to 35 for the smaller species; it scales with body mass-0.199 at 35 degrees C. The maximal metabolic rate of 6.36 mL O2 g-1 h-1 for Varanus caudolineatus is the highest recorded for any squamate. Variations from the interspecific regression line appear to have some ecological significance. Varanus tristis (a widely foraging arboreal goanna) and Varanus eremius (a widely foraging terrestrial goanna) have a higher standard metabolic rate than Varanus acanthurus (a sedentary terrestrial goanna). The three arboreal goannas (Varanus caudolineatus, Varanus gilleni, and Varanus tristis) have a higher maximal metabolic rate than the terrestrial species (Varanus brevicauda, V. eremius, V. acanthurus, Varanus gouldii, Varanus rosenbergi, and Varanus panoptes).

Effects of urea on M4-lactate dehydrogenase from elasmobranchs and urea-accumulating Australian desert frogs

We measured the effect of urea on M4-lactate dehydrogenase (M4-LDH) from elasmobranchs and Australian desert frogs (urea accumulators) and from two animals that do not accumulate urea, the axolotl and the rabbit. An analysis of the effect of urea on the Kd(NADH), V, V/K(m(prr)) and V/K(m(NADH)) shows that in all cases the major effect of urea was on the binding of pyruvate, which fits with data in the literature that show that urea acts as a competitive inhibitor of LDH. The characteristics of the elasmobranch enzymes are consistent with a proposed adaptation model, but the situation for the enzymes from the aestivating frogs is equivocal. Urea (400 mM) had less effect on the K(m(prr)) of M4-LDH from the urea accumulators than it did on the non-accumulators, suggesting a general adaptation and that the enzyme produced by the aestivating frogs (urea accumulators) is kinetically different from that of non-aestivating frogs (non-accumulators). A new approach is used to characterize the overall pattern of adaptation to urea. The pattern is similar in an enzyme from an elasmobranch and an aestivating frog despite the temporary presence of urea in the latter and the phylogenetic difference between these animals.

Temperature regulation and metabolism of an Australian bat, Chalinolobus gouldii (Chiroptera:Vespertilionidae) when euthermic and torpid

The thermal and metabolic physiology of Chalinolobus gouldii, an Australian vespertilionid bat, was studied in the laboratory using flow-through respirometry. Chalinolobus gouldii exhibits a clear pattern of euthermic thermoregulation, typical of endotherms with respect to body temperature and rate of oxygen consumption. The basal metabolic rate of euthermic Chalinolobus gouldii is approximately 86% of that predicted for a 17.5-g mammal and falls into the range of mass-specific basal metabolic rates ascribed to vespertilionid bats. However, like most vespertilionid bats, Chalinolobus gouldii displays extreme thermolability. It is able to enter into torpor and spontaneously arouse at ambient temperatures as low as 5 degrees C. Torpid bats thermoconform at moderate ambient temperature, with body temperature approximately ambient temperature, and have a low rate of oxygen consumption determined primarily by Q10 effects. At low ambient temperature (< 10 degrees C), torpid C. gouldii begin to regulate their body temperature by increased metabolic heat production; they tend to maintain a higher body temperature at low ambient temperature than do many northern hemisphere hibernating bats. Use of torpor leads to significant energy savings. The evaporative water loss of euthermic bats is relatively high, which seems unusual for a bat whose range includes extremely arid areas of Australia, and is reduced during torpor. The thermal conductance of euthermic C. gouldii is less than that predicted for a mammal of its size. The thermal conductance is considerably lower for torpid bats at intermediate body temperature and ambient temperature, but increases to euthermic values for torpid bats when thermoregulating at low ambient temperature.

Effectors of metabolic depression in an estivating pulmonate snail (Helix aspersa): whole animal and in vitro tissue studies

We have examined metabolic depression in the land snail (Helix aspersa) during estivation, and have developed a tissue model of metabolic depression using an in vitro mantle preparation. The metabolic rate of H. aspersa is depressed by 84% in vivo within 4 weeks of onset of estivation, and this metabolic depression is accompanied by a decrease in haemolymph PO2 and pH, and an increase in haemolymph PCO2. The in vitro mantle preparation has a stable O2 consumption and energy charge, and an energy charge similar to that of mantle in vivo. The in vitro mantle is an O2-conforming tissue, with VO2 varying curvilinearly with PO2. Consequently, we have developed a mathematical method of calculating tissue VO2 at any PO2. These calculations show that under appropriate incubation conditions of pH and PO2, the mantle from estivating animals shows a stable in vitro metabolic depression of 48% compared to mantle from control snails. The extrinsic effects of PO2 and pH account for 70% of the total in vitro metabolic depression of mantle tissue; intrinsic effectors contribute a further 30%.

Oxygen consumption by ammocoetes of the lamprey Geotria australis in air

When covered by moistened lint-free gauze, the larvae (ammocoetes) of the lamprey Geotria australis survived, without apparent discomfort, for 4 days in water-saturated air at 10, 15 and 20 degrees C. In air, the mean standard rates of O2 consumption of medium to large ammocoetes of G. australis (mean = 0.52 g) at 10, 15 and 20 degrees C were 14.5, 35.7 and 52.1 microliters.g-1.h-1, respectively. At 15 degrees C, the slope of the relationship between log O2 consumption (microliter O2.h-1) and log body weight for ammocoetes over a wide range in body weight was 0.987. The Q10s for rate of O2 consumption between 10 and 15 degrees C, 15 and 20 degrees C and 10 and 20 degrees C were 4.9, 2.9 and 3.6, respectively. Our results and observations of the ammocoetes suggest that, when out of water, larval G. australis derives most of its O2 requirements from cutaneous respiration, particularly at lower temperatures. This would be facilitated by the small size and elongate shape (and thus a relatively high surface-to-volume ratio), low metabolic rate, thin dermis, extensive subdermal capillary network and high haemoglobin concentration of larval G. australis.

Do Australian desert frogs co-accumulate counteracting solutes with urea during aestivation?

Australian desert frogs of the genera Neobatrachus, Cyclorana and Heleioporus experience significant dehydration, and iono- and osmoconcentration, during aestivation in the laboratory and accumulate substantial amounts of urea (100-200 mmol)(l-1). We expected a priori that aestivating frogs probably would not need to accumulate balancing osmolytes but would accumulate trimethylamine oxide (TMAO) or betaine as counteracting solutes to urea. These aestivating frogs did not co-accumulate a substantial quantity of any particular balancing osmolyte or counteracting solute, such as a methylamine [TMAO, trimethylamine amine (TMA), betaine, sarcosine, glycerophosphorylcholine (GPC)] or polyol (inositol, mannitol, sorbitol) in plasma or muscle relative to urea accumulation. However, for aestivating frogs, the total concentration of all measured methylamines and polyols (TMAO + TMA + betaine + sarcosine + GPC + inositol) in muscle was approximately 35-45 mmol kg-1, and so it is possible that all of these solutes have a combined counteracting osmolyte role in aestivating frogs at a ratio to urea of approximately 1:2.5, as has been described for elasmobranch fishes. Alternatively, the absence of substantial co-accumulation with urea of any particular solute suggests that aestivating frogs might not require any major extracellular or intracellular counteracting solutes (TMAO, betaine, GPC). The enzyme systems of these aestivating frogs may be insensitive to the perturbing effects of urea, or the perturbing effects of accumulated urea may be a mechanism for metabolic depression, during aestivation.

Water and Energy Balance of Captive and Free-Ranging Spinifexbirds (Eremiornis Carteri) North (Aves:Sylviidae) on Barrow Island, Western Australia

The mean annual rainfall of Barrow Island, located about 90 km north of Onslow off the arid Western Australian coast, is 324 mm, 74% of which falls as cyclonic rain between February and May. Spinifexbirds captured in May 1992 had a mean body mass of 12.3 +/- 0.3 g and a total body water content (TBW) of 774 +/- 1.6%. In December 1992 the mean body mass was significantly lower (11.7 +/- 0.2 g; P < 0.05), despite a TBW of 73.4 +/- 1.0%. Spinifexbirds maintained water balance in both seasons, but water flux rates were significantly higher in May (P = 0.01). Respective influx and efflux rates in May were 0.70 +/- 0.30 and 0.72 +/- 0.03 mL (g day)(-1) compared with 0.60 +/- 0.04 and 0.57 +/- 0.04 mL (g day)(-1) in December. Field metabolic rates (FMRs), measured with doubly-labelled water ((3)HH(18)0), did not differ significantly between the two periods. The mean FMR in May was 6.8 +/- 0.6 mL CO2 (g h)(-1) compared with 7.2 +/- 0.9 mL CO2 (g h)(-1) in December, similar to rates predicted by Nagy and Peterson (1988) for a similar-sized passerine. The thermoneutral zone (TNZ) of spinifexbirds, determined by metabolic laboratory trials in December, extended from 30 to 39 degrees C. The standard metabolic rate (SMR) within the TNZ was 2.9 +/- 0.1 mL O-2 (g h)(-1), which is up to 20% lower than predicted values. Body temperature was maintained at 39.1 degrees C in the TNZ, but birds became hyperthermic at ambient temperatures (T(a)s) higher than 35 degrees C, with body temperatures reaching 44 degrees C. Wet thermal conductance and evaporative water loss increased markedly at T(a)s > 35 degrees C. The data suggest that spinifexbirds have limited physiological adaptations to desert conditions compared with some other arid-zone birds.

Dracunculiasis eradication: March 1994 update

Substantial progress has been realized in the global campaign to eradicate dracunculiasis by the end of 1995 since a previous review of the subject was published in this journal a year ago. All known endemic countries are now engaged in the eradication effort, and one or more control measures are now in place in 93% of endemic villages. Despite improved surveillance for the disease, the number of reported cases of the disease has been reduced by 41% (to about 221,000), and the number of known endemic villages has been reduced by 28% (to about 16,500) in the past year. Priorities for national eradication programs in 1994 include increasing the use of vector control and intensifying the case containment strategy in endemic villages. It is still possible to achieve the eradication target of December 1995, but greatly intensified efforts this year will be required to do so.

Cocoon Formation and Structure in the Estivating Australian Desert Frogs, Neobatrachus and Cyclorana

Formation of a cocoon during aestivation is described for the Australian hylid frogs Cyclorana maini, C. novaehollandiae and C. platycephala, and the myobatrachid frogs Neobatrachus aquilonius, N. centralis, N. fulvus, N. kunapalari, N. pelobatoides, N. sudelli, N. sutor and N. wilsmorei. At the onset of aestivation, these frogs assume a 'water-conserving' posture and become inactive. A thin, transparent cocoon is observed to form within a week of onset of inactivity, and becomes progressively thicker and more opaque. The cocoon covers the entire body surface, including mouth, eyes and cloaca, except for the narial openings. The cocoon consists of an accumulation of multiple layers of single-cell-thick sheets of outer epidermal cells, formed at regular periods of about every two days (Cyclorana) to four days (Neobatrachus), that correspond to the normal shedding frequency. Each layer of the cocoon has a thickness of about 0.4 mu m (Cyclorana) to 0.6 mu m (Neobatrachus). The thickness of the cocoon and the number of layers increase progressively with duration of aestivation.

Field Metabolism and Turnover in the Golden Bandicoot (Isoodon-Auratus) and Other Small Mammals From Barrow Island, Western-Australia

Barrow Island, which lies about 90 km north of Onslow off the arid Western Australian Pilbara coast, experienced its driest year on record in 1990 with a total of only 122.4 mm of rain. Golden bandicoots captured in November 1990 evidenced poor condition and mean body mass was a low 242.6 +/- 10.9 g with-a total body water content (TBW) of 76.3 +/- 1.4%. Despite this substantial loss of body water and solids, the animals maintained water and electrolyte balance during the period of turnover [water influx 79.5 +/- 6.9 v. efflux 83.3 +/- 5-7 mL (kg0.82 day)-1 and sodium influx 4.9 +/- 0.7 v. efflux 5.3 +/- 0.7 mmol (kg day)-1]. By April 1991, although only a further 37.4 mm of rain had been recorded on Barrow Island, the condition of the bandicoots had improved markedly, as a result of exploitation of insect resources, and their mean body mass had increased to 306.5 +/- 22.6 g and TBW decreased to 62.5 +/- 1.4% (both P < 0.001), the latter reflecting enhanced fat stores. This general improvement in condition of the bandicoots was in marked contrast to that of other herbivorous marsupials on the island. Rates of water and sodium turnover of the golden bandicoots were, however, not significantly different from those measured in the previous November, Field Metabolic Rates (FMRs), measured with doubly labelled water ((HHO))-H-3-O-18, were extremely low, averaging only 0.45 +/- 0.26 mL CO2 (g h)-1, which is very close to laboratory estimates of 0.35 +/- 0.09 mL O2(g h)-1 for the basal metabolic rate of this species. A major cyclone struck Barrow Island on 3 March 1992, with 162 mm of rain falling in 24 h, and turnover measurements in May of that year revealed a substantial increase in rates of water flux. Mean body mass further increased to 332.6 +/- 8.5 g and TBW averaged 61.8 +/- 1.1%. Water turnover rates were significantly elevated when compared with April of the previous year with an influx of 112.5 +/- 7.3 and an efflux of 119.0 +/- 7.6 mL (kg0.82 day)-1 respectively (both P = 0.001). Rates of sodium turnover, however, were only slightly lower at 3.6 +/- 0.5 and 4.1 +/- 0.5 mmol (kg day)-1 for influx and efflux respectively (P = 0.056 for influx only), suggesting a slight decrease in the average sodium content of the diet. The volume of water required to maintain hygric balance was estimated by regression analysis at 26.7 mL day-1 [=88.3 mL (kg0.82 day)-1] in November 1990, and 33-9 mL day-1 [=85.2 mL (kg0.82 day)-1] in May 1992, following rain. The FMR of eight bandicoots was very significantly elevated to 1.39 +/- 0.23 mL CO2 (g h)-1 after rain, which is substantially higher than even the FMR of 0.91 +/- 0.07 mL CO2(g h)-1, or 644 kJ day-1, reported for the closely related southern brown bandicoot (Isoodon obesulus) studied in the region of Perth by Nagy et al. (1991). Turnover rates of water and sodium for two rodent species, the Barrow Island mouse (Pseudomys nanus) and the rock rat (Zyzomys argurus), were very similar to those recorded for golden bandicoots in the dry period, but FMRs were a little higher at 0.80 +/- 0.26 and 0.59 +/- 0-36 mL CO2(g h)-l respectively. The FMR of Barrow Island mice increased very significantly to a mean of 2.73 +/- 0.50 mL CO2(g h)-l after rain, but rock rats were not caught at this time. The data document the impressive ability of these mammals to avail themselves of extremely limited resources and maintain physiological homoiostasis under conditions of extreme aridity.

Kidney Structure and Renal Indexes of Dasyurid Marsupials

Examination of kidney structure for 25 dasyurid marsupials showed that kidneys of species from arid habitats tend to have a relatively thicker medulla and higher renal indices than those of species from semi-arid, mesic and tropical areas. Arid-dwelling species such as Ningaui ridei and Pseudantechinus macdonnellensis had the highest renal indices while Antechinus swainsonii, collected from alpine environments, had the lowest renal index values. Renal indices were significantly correlated also with body weight, average daily maximum temperature and average annual rainfall of the habitat. The renal indices for xeric species differed significantly by discriminant analysis from the indices for other species. There was no obvious phylogenetic conservatism in renal indices; for example, renal indices varied almost as much within the genus Sminthopsis as between all of the other genera of Dasyuridae examined.