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Species with broad geographic ranges may experience varied environmental conditions throughout their range leading to local adaptation. Variation among populations reflects potential adaptability or plasticity, with implications for populations impacted by disease, climate change, and other anthropogenic influences. However, behavior may counteract divergent selection among populations. We studied intraspecific variation in hibernation physiology of Myotis lucifugus (little brown myotis) and Corynorhinus townsendii (Townsend's big-eared bat), two species of bats with large geographic ranges. We studied M. lucifugus at three hibernacula which spanned a latitudinal gradient of 1500 km, and C. townsendii from 6 hibernacula spread across 1200 km latitude and 1200 km longitude. We found no difference in torpid metabolic rate among populations of either species, nor was there a difference in the effect of ambient temperature among sites. Evaporative water loss was similar among populations of both species, with the exception of one C. townsendii pairwise site difference and one M. lucifugus site that differed from the others. We suggest the general lack of geographic variation is a consequence of behavioral microhabitat selection. As volant animals, bats can travel relatively long distances in search of preferred microclimates for hibernation. Despite dramatic macroclimate differences among populations, hibernating bats are able to find preferred microclimate conditions within their range, resulting in similar selection pressures among populations spread across wide geographic ranges. [ABSTRACT FROM AUTHOR]

Environmental humidity is thought to be a major determinant of evaporative cooling capacity at high air temperatures (Ta), but the technical challenges of experimentally manipulating humidity in respirometry chambers have resulted in far less being known about the effects of humidity compared to those of Ta. We tested the prediction that at Ta approaching and exceeding normothermic body temperature (Tb), high humidity would result in higher Tb, lower evaporative water loss (EWL) and/or higher resting metabolic rate (RMR) in a passerine bird, the white-browed sparrow-weaver (Plocepasser mahali). We used open-system flow-through respirometry to measure EWL, RMR and Tb in sparrow-weavers experiencing Ta = 36-44 °C and chamber humidities of 6, 13, 19 or 25 g m− 3. Increasing humidity was associated with significantly higher Tb. The strongest effect of humidity, however, involved significant increases in RMR; at Ta = 40 °C, RMR at a humidity of 25 g m− 3 was ~ 40% higher compared to a humidity of 6 g m− 3. Moreover, the interaction between Ta and humidity exerted a significant effect on the ratio of evaporative heat loss (EHL) to metabolic heat production (MHP), evident as an increasing effect of humidity with increasing Ta. Our results, when compared with those of the limited number of previous studies that involved similar ranges of Ta and humidity, reveal that the relative effects of humidity on EWL and RMR vary among avian taxa, and support the notion that the overall effect of high humidity is a reduction in maximum EHL/MHP. [ABSTRACT FROM AUTHOR]

Much recent work on avian physiological adaptation to desert environments has focused on larks (Passeriformes: Alaudidae). We tested the prediction that the threatened red lark (Calendulauda burra), a species restricted to very arid parts of South Africa and which is not known to drink, exhibits highly efficient evaporative cooling and makes pronounced use of facultative hyperthermia when exposed to high air temperatures (Ta). We also predicted that C. burra possesses similarly low basal metabolic rate (BMR) and total evaporative water loss (EWL) at moderate Ta as reported for species from the deserts of the Middle East. Rest-phase thermoregulation in C. burra was characterized by an unusually low lower critical limit of thermoneutrality at Ta = ~ 21 °C and a BMR of 0.317 ± 0.047 W, the lowest BMR relative to allometrically-expected values yet reported in any lark. During the diurnal active phase, red larks were able to tolerate Ta up to 50 °C, with the onset of panting occurring at Ta = 38 °C. Maximum EWL was 1.475 ± 0.107 g h− 1 at Ta = 50 °C, equivalent to 620% of minimum EWL at thermoneutrality. The maximum ratio of evaporative heat dissipation to metabolic heat production was 1.58, a value towards the lower end of the range reported for passerines. Our data support the prediction that C. burra shows metabolic traits similar to those of other larks inhabiting extremely arid climates, but not the notion that evaporative cooling at high Ta in this species is more efficient than in most passerines. [ABSTRACT FROM AUTHOR]

Nightjars represent a model taxon for investigating physiological limits of heat tolerance because of their habit of roosting and nesting in sunlit sites during the heat of the day. We investigated the physiological responses of Rufous-cheeked nightjars ( Caprimulgus rufigena) and Freckled nightjars ( Caprimulgus tristigma) to high air temperatures ( T ) by measuring body temperature ( T ), resting metabolic rate (RMR) and total evaporative water loss (TEWL) at T ranging from 10 to 56 °C. Both species became hyperthermic at T > T . Lower critical limits of thermoneutrality occurred at T between 35 and 37 °C, whereas we detected no clear upper critical limits of thermoneutrality. Between T ≈ 37.0 and 39.9 °C, rates of TEWL increased rapidly with T . At T ≥ 40 °C, fractional increases in mass-specific TEWL rates were 78-106% of allometric predictions. Increasing evaporative heat dissipation incurred only small metabolic costs, with the RMR of neither species ever increasing by more than 20% above thermoneutral values. Consequently, both species displayed extremely efficient evaporative cooling; maximum evaporative heat dissipation was equivalent to 515% of metabolic heat production (MHP) at T ≈ 56 °C in C. rufigena and 452% of MHP at T ≈ 52 °C in C. tristigma. Our data reiterate that caprimulgids have evolved an efficient mechanism of evaporative cooling via gular fluttering, which minimizes metabolic heat production at high T and reduces total heat loads. This likely aids in reducing TEWL rates and helps nightjars cope with some of the most thermally challenging conditions experienced by any bird. [ABSTRACT FROM AUTHOR]

Seasonal variation in metabolic rate and evaporative water loss as a function of ambient temperature were compared in two species of bees. The endemic blue-banded bee, Amegilla chlorocyanea, is a solitary species that is an important pollinator in the south-west Australian biodiversity hotspot. Responses were compared with the European honeybee, Apis mellifera, naturalised in Western Australia almost 200 years ago. Metabolic rate increased exponentially with temperature to a peak in both species, and then declined rapidly, with unique scaling exponents and peaks for all species-by-season comparisons. Early in the austral summer, Apis was less thermally tolerant than Amegilla, but the positions reversed later in the foraging season. There were also significant exponential increases in evaporative water loss with increasing temperature, and both season and species contributed to significantly different responses. Apis maintained relatively consistent thermal performance of metabolic rate between seasons, but at the expense of increased rates of evaporative water loss later in summer. In contrast, Amegilla had dramatically increased metabolic requirements later in summer, but maintained consistent thermal performance of evaporative water loss. Although both species acclimated to higher thermal tolerance, the physiological strategies underpinning the acclimation differed. These findings may have important implications for understanding the responses of these and other pollinators to changing environments and for their conservation management. [ABSTRACT FROM AUTHOR]

The few within-species studies on the effects of long-term captivity on avian physiological variables have small samples sizes and contradictory results. Nevertheless, many physiological studies make use of long-term captive birds, assuming the results will be applicable to wild populations. Here we investigated the effects of long-term captivity on a variety of physiological measurements in a relatively small (~12 g) southern African endemic bird, the Cape white-eye ( Zosterops virens). Whole animal basal metabolic rate (BMR) and body mass (Mb) were influenced more by long-term captivity than by season, while mass-specific BMR, standard and basal whole animal and mass-specific evaporative water loss (EWL), and respiratory quotient (RQ), were all affected primarily by season, with long-term captivity having less of an effect. We therefore caution that whole animal BMR and Mb of long-term captive birds should not be used as representative of wild populations, and that the origin of study birds should be considered when comparing EWL and RQ of wild and long-term captive birds. [ABSTRACT FROM AUTHOR]

Bats in hot roosts experience some of the most thermally challenging environments of any endotherms, but little is known about how heat tolerance and evaporative cooling capacity vary among species. We investigated thermoregulation in three sympatric species ( Nycteris thebaica, Taphozous mauritianus and Sauromys petrophilus) in a hot, semi-arid environment by measuring body temperature ( T), metabolic rate and evaporative water loss (EWL) at air temperatures ( T) of 10-42 °C. S. petrophilus was highly heterothermic with no clear thermoneutral zone, and exhibited rapid increases in EWL at high T to a maximum of 23.7 ± 7.4 mg g h at T ≈ 42 °C, with a concomitant maximum T of 43.7 ± 1.0 °C. T. mauritianus remained largely normothermic at Ts below thermoneutrality and increased EWL to 14.7 ± 1.3 mg g h at T ≈ 42 °C, with a maximum T of 42.9 ± 1.6 °C. In N. thebaica, EWL began increasing at lower T than in either of the other species and reached a maximum of 18.6 ± 2.1 mg g h at T = 39.4 °C, with comparatively high maximum T values of 45.0 ± 0.9 °C. Under the conditions of our study, N. thebaica was considerably less heat tolerant than the other two species. Among seven species of bats for which data on T as well as roost temperatures in comparison to outside T are available, we found limited evidence for a correlation between overall heat tolerance and the extent to which roosts are buffered from high T. [ABSTRACT FROM AUTHOR]

Duration and start time of respirometry experiments have significant effects on the measurement of basal values for several commonly measured physiological variables (metabolic rate, evaporative water loss and body temperature). A longer measurement duration reduced values for all variables for all start times, and this was an effect of reduced animal activity rather than random sampling. However, there was also an effect of circadian rhythm on the timing of minimal physiological values. Experiment start time had a significant effect on time taken to reach minimal values for all variables, ranging from 0400 hours ± 38 min (body temperature, start time 2300 hours) to 0854 hours ± 52 min (evaporative water loss, start time 1700 hours). It also influenced the time of day that minimal values were obtained, ranging from 2224 hours ± 40 min (carbon dioxide production, start time 1500 hours) to 0600 hours ± 57 min (oxygen consumption, start time 2300 hours), and the minimum values measured. Consequently, both the measurement duration and the experiment start time should be considered in experimental design to account for both a handling and a circadian effect on the animal's physiology. We suggest that experiments to measure standard physiological variables for small diurnal birds should commence between 1700 and 2100 hours, and measurement duration should be at least 9 h. [ABSTRACT FROM AUTHOR]

Quolls ( Dasyurus) are medium-sized carnivorous dasyurid marsupials. Tiger (3,840 g) and eastern quolls (780 g) are mesic zone species, northern quolls (516 g) are tropical zone, and chuditch (1,385 g) were once widespread through the Australian arid zone. We found that standard physiological variables of these quolls are consistent with allometric expectations for marsupials. Nevertheless, inter-specific patterns amongst the quolls are consistent with their different environments. The lower Tb of northern quolls (34°C) may provide scope for adaptive hyperthermia in the tropics, and they use torpor for energy/water conservation, whereas the larger mesic species (eastern and tiger quolls) do not appear to. Thermolability varied from little in eastern (0.035°C °C−1) and tiger quolls (0.051°C ºC−1) to substantial in northern quolls (0.100°C ºC−1) and chuditch (0.146°C ºC−1), reflecting body mass and environment. Basal metabolic rate was higher for eastern quolls (0.662 ± 0.033 ml O2 g−1 h−1), presumably reflecting their naturally cool environment. Respiratory ventilation closely matched metabolic demand, except at high ambient temperatures where quolls hyperventilated to facilitate evaporative heat loss; tiger and eastern quolls also salivated. A higher evaporative water loss for eastern quolls (1.43 ± 0.212 mg H2O g−1 h−1) presumably reflects their more mesic distribution. The point of relative water economy was low for tiger (−1.3°C), eastern (−12.5°C) and northern (+3.3) quolls, and highest for the chuditch (+22.6°C). We suggest that these differences in water economy reflect lower expired air temperatures and hence lower respiratory evaporative water loss for the arid-zone chuditch relative to tropical and mesic quolls. [ABSTRACT FROM AUTHOR]

The honey possum is the only non-volant mammal to feed exclusively on a diet of nectar and pollen. Like other mammalian and avian nectarivores, previous studies indicated that the honey possum’s basal metabolic rate was higher than predicted for a marsupial of equivalent body mass. However, these early measurements have been questioned. We re-examined the basal metabolic rate (2.52 ± 0.222 ml O2 g−1 h−1) of the honey possum and confirm that it is indeed higher (162%) than predicted for other marsupials both before and after accounting for phylogenetic history. This, together with its small body mass (5.4 ± 0.14 g; 1.3% of that predicted by phylogeny) may be attributed to its nectarivorous diet and mesic distribution. Its high-basal metabolic rate is associated with a high-standard body temperature (36.6 ± 0.48°C) and oxygen extraction (19.4%), but interestingly the honey possum has a high point of relative water economy (17.0°C) and its standard evaporative water loss (4.33 ± 0.394 mg H2O g−1 h−1) is not elevated above that of other marsupials, despite its mesic habitat and high dietary water intake. [ABSTRACT FROM AUTHOR]

Parental care provides considerable benefits to offspring and is widespread among animals, yet it is relatively uncommon among squamate reptiles (e.g., lizards and snakes). However, all pythonine snakes show extended maternal egg brooding with some species being facultatively endothermic. While facultative endothermy provides thermal benefits, the presence of brooding in non-endothermic species suggests other potential benefits of brooding. In this study we experimentally tested the functional significance of maternal brooding relative to water balance in the children’s python, Antaresia childreni, a small species that does not exhibit facultative endothermy. Clutch evaporative water loss (EWL) was positively correlated with clutch mass and was much lower than expected values based on individual eggs. The conglomerate clutch behaved as a single unit with a decreasing surface area to volume ratio as clutch size increased. Maternal brooding had a dramatic impact on evaporation from eggs, reducing and possibly eliminating clutch EWL. In a separate experiment, we found that viability of unattended eggs is highly affected by humidity level, even in the narrow range from 75 to 100% relative humidity at 30.5°C (20–33 mg m−3 absolute humidity). However, the presence of the brooding female ameliorated this sensitivity, as viability of brooded clutches at 75% relative humidity was higher than that of non-brooded eggs at either the same absolute humidity or at near-saturated conditions. Overall, these results demonstrate that brooding behavior strongly promotes egg water balance (and thus egg viability) in children’s pythons. [ABSTRACT FROM AUTHOR]

Metabolic rate and evaporative water loss (EWL) were measured for a small, arid-zone marsupial, the stripe-faced dunnart ( Sminthopsis macroura), when normothermic and torpid. Metabolic rate increased linearly with decreasing ambient temperature ( Ta) for normothermic dunnarts, and calculated metabolic water production (MWP) ranged from 0.85±0.05 ( Ta=30°C) to 3.13±0.22 mg H2O g−1 h−1 ( Ta=11°C). Torpor at Ta=11 and 16°C reduced MWP to 24–36% of normothermic values. EWL increased with decreasing Ta, and ranged from 1.81±0.37 ( Ta=30°C) to 5.26±0.86 mg H2O g−1 h−1 ( Ta=11°C). Torpor significantly reduced absolute EWL to 23.5–42.3% of normothermic values, resulting in absolute water savings of 50–55 mg H2O h−1. The relative water economy (EWL/MWP) of the dunnarts was unfavourable, remaining >1 at all Ta investigated, and did not improve with torpor. Thus torpor in stripe-faced dunnarts results in absolute, but not relative, water savings. [ABSTRACT FROM AUTHOR]

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 °C. Torpid bats thermoconform at moderate ambient temperature, with body temperature ≈ ambient temperature, and have a low rate of oxygen consumption determined primarily by Q10 effects. At low ambient temperature (< 10 °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. [ABSTRACT FROM AUTHOR]

The purpose of this study is to examine diurnal variation in several thermal and metabolic parameters of the golden hamster, Mesocricetus auratus. Metabolic rate, core temperature, and evaporative water loss were measured during night and day at several ambient temperatures. Wet minimal thermal conductance, dry minimal thermal conductance, basal metabolic rate, minimal net heat production and the lower critical temperature difference were estimated from these measurements. Wet and dry minimal thermal conductance, evaporative water loss, core temperature, basal metabolic rate, and lower critical temperature difference were greater during the active phase than during the resting phase. The diurnal variation in wet minimal thermal conductance was much smaller than that predicted from published allometric equations. The diurnal variation in wet minimal thermal conductance was 9% of the 24-h mean. The diurnal variation in dry minimal thermal conductance was 26% of the 24-h mean. The higher active-phase core temperature and basal metabolic rate may function to enhance peak metabolic performance during the active phase. The lower resting phase metabolism and core temperature may reduce energetic costs. The greater active-phase lower critical temperature difference may be a result of the greater active-phase basal metabolic rate. Diurnal variation in minimal thermal conductance may be caused by changes in peripheral circulation. [ABSTRACT FROM AUTHOR]

The effect of clustering behaviour on metabolism, body temperature, thermal conductance and evaporative water loss was investigated in speckled mousebirds at temperatures between 5 and 36°C. Within the thermal neutral zone (approximately 30-35 °C) basal metabolic rate of clusters of two birds (32.5 J·g·h) and four birds (28.5 J·g·h) was significantly lower by about 11% and 22%, respectively, than that of individuals (36.4 J·g·h). Similarly, below the lower critical temperature, the metabolism of clusters of two and four birds was about 14% and 31% lower, respectively, than for individual birds as a result of significantly lower total thermal conductance in clustered birds. Body temperature ranged from about 36 to 41°C and was positively correlated with ambient temperature in both individuals and clusters, but was less variable in clusters. Total evaporative water loss was similar in individuals and clusters and averaged 5-6% of body weight per day below 30°C in individuals and below 25°C in clusters. Above these temperatures total evaporative water loss increased and mousebirds could dissipate between 80 and 90% of their metabolic heat production at ambient temperatures between 36 and 39°C. Mousebirds not only clustered to sleep between sunset and sunrise but were also observed to cluster during the day, even at high ambient temperature. Whereas clustering at night and during cold, wet weather serves a thermoregulatory function, in that it allows the brrds to maintain body temperature at a reduced metabolic cost, clustering during the day is probably related to maintenance of social bonds within the flock. [ABSTRACT FROM AUTHOR]