scholarly journals Thermoregulatory role of insensible evaporative water loss constancy in a heterothermic marsupial

2017 ◽  
Vol 13 (11) ◽  
pp. 20170537 ◽  
Author(s):  
Christine Elizabeth Cooper ◽  
Philip Carew Withers

‘Insensible’ evaporative water loss of mammals has been traditionally viewed as a passive process, but recent studies suggest that insensible water loss is under regulatory control, although the physiological role of this control is unclear. We test the hypothesis that regulation of insensible water loss has a thermoregulatory function by quantifying for the first time evaporative water loss control, along with metabolic rate and body temperature, of a heterothermic mammal during normothermia and torpor. Evaporative water loss was independent of ambient relative humidity at ambient temperatures of 20 and 30°C, but not at 25°C or during torpor at 20°C. Evaporative water loss per water vapour pressure deficit had a positive linear relationship with relative humidity at ambient temperatures of 20 and 30°C, but not at 25°C or during torpor at 20 or 25°C. These findings suggest that insensible water loss deviates from a physical model only during thermoregulation, providing support for the hypothesis that regulation of insensible evaporative water loss has a thermoregulatory role.

2014 ◽  
Vol 281 (1784) ◽  
pp. 20140149 ◽  
Author(s):  
Philip C. Withers ◽  
Christine E. Cooper

It is a central paradigm of comparative physiology that the effect of humidity on evaporative water loss (EWL) is determined for most mammals and birds, in and below thermoneutrality, essentially by physics and is not under physiological regulation. Fick's law predicts that EWL should be inversely proportional to ambient relative humidity (RH) and linearly proportional to the water vapour pressure deficit (Δwvp) between animal and air. However, we show here for a small dasyurid marsupial, the little kaluta ( Dasykaluta rosamondae ), that EWL is essentially independent of RH (and Δwvp) at low RH (as are metabolic rate and thermal conductance). These results suggest regulation of a constant EWL independent of RH, a hitherto unappreciated capacity of endothermic vertebrates. Independence of EWL from RH conserves water and heat at low RH, and avoids physiological adjustments to changes in evaporative heat loss such as thermoregulation. Re-evaluation of previously published data for mammals and birds suggests that a lesser dependence of EWL on RH is observed more commonly than previously thought, suggesting that physiological independence of EWL of RH is not just an unusual capacity of a few species, such as the little kaluta, but a more general capability of many mammals and birds.


2017 ◽  
Vol 284 (1867) ◽  
pp. 20171478 ◽  
Author(s):  
E. C. Eto ◽  
P. C. Withers ◽  
C. E. Cooper

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.


1978 ◽  
Vol 29 (1) ◽  
pp. 161 ◽  
Author(s):  
PS Hopkins ◽  
GI Knights ◽  
AS Le Feuvre

Rectal temperature measurements of tropical Merino sheep taken in the sun during summer indicated that there were high and low temperature groups. Animals of low temperature status (e.g. 39.4°C) also exhibited a low respiration rate (e.g. 110/min) in comparison with their less adapted counterparts (40.0° and 190/min). These differences were greatest when ambient temperatures were high. The repeatability of temperature status was 0.46 (P < 0.01). Animals of folds (+) phenotype had significantly higher rectal temperatures than folds (–) animals (P < 0.05). Shearing caused a marked but transient increase in rectal temperature. Compensatory mechanisms apparently involved an increase in cutaneous heat dissipation and/or a decrease in exogenous heat load. Evaporative water loss (80–115 ml/kg/day) greatly exceeded the non-evaporative water loss (40–65 ml/kg/day) of sheep in metabolism cages. Respiratory water loss could account for only 8–10% of the total daily evaporative water loss. Non-respiratory evaporative water loss (as measured by difference) was c. 75–100 ml/kg/day. There were no striking differences between high and low temperature status sheep in this regard. Measurements of respiratory (2 ml/kg/hr) and non-respiratory (5.5 ml/kg/hr) evaporative water loss made in hygrometric tents suggested that the greater non-respiratory water loss was partly due to a higher rate of loss and partly to a longer period of loss per day. This suggestion was supported by the diurnal patterns of rectal temperatures and respiration rates reported here, though no firm conclusions could be made as to the thermotaxic effect of non-respiratory water loss and thermoregulation of tropical Merinos with varying amounts of wool cover.


1976 ◽  
Vol 87 (3) ◽  
pp. 527-532 ◽  
Author(s):  
S. A. Richards

SummaryThe rate of evaporative water loss has been studied in domestic fowls in the ambient temperature range from 0 to 40°C.Results for whole-body evaporation were similar when obtained by the open-flow and direct-weighing methods. At low levels of absolute humidity the rate increased by 0·03 mg/(g.h.°C) from 0 to 22 °C and by 0·17 mg/(g.h.°C) from 23 to 40 °C. Wholebody evaporation decreased with rising ambient water vapour pressure by 0·7 mg/(g.h.kPa).Cutaneous water loss was greater than respiratory water loss below 21 °C; it accounted for 78% of whole-body evaporation at 0 °C, falling to 25% at 40 °C.The rates of respiratory and whole-body evaporation could both be expressed as linear functions of respiratory frequency.


2014 ◽  
Vol 92 (1) ◽  
pp. 81-86 ◽  
Author(s):  
Michaël Guillon ◽  
Gaëtan Guiller ◽  
Dale F. DeNardo ◽  
Olivier Lourdais

Terrestrial ectotherms predominantly use behavioural means to thermoregulate and thereby optimize performances. However, thermoregulation can impart physiological challenges to other critical processes such as water balance by increasing evaporative water loss (EWL). Like thermoregulation, water balance is influenced by both external factors (e.g., microhabitat and environmental constraints) and endogenous traits (e.g., evaporative water loss rates, dehydration tolerance). Although thermoregulation and water balance are tightly linked, the role of water balance is often overlooked when evaluating species climatic adaptation and response to global warming. We studied two congeneric viperid species (the Aspic Viper, Vipera aspis (L., 1758), and the Common Viper, Vipera berus (L., 1758)) with contrasted climatic affinities (south European versus boreal, respectively). These parapatric species are syntopic in narrow contact zones where microhabitat partitioning has been reported. We compared total EWL and cutaneous evaporative water loss (CEWL) of the two species and monitored the thermal and hydric conditions of the microhabitats used in syntopic populations. We found that the boreal V. berus has greater EWL, both total and cutaneous. Accordingly, this species selected more humid microhabitats throughout the year. Humidity appears to be an important determinant of habitat selection, and therefore, V. berus is likely vulnerable to changing precipitation at the southern limit of its distribution.


1986 ◽  
Vol 34 (1) ◽  
pp. 35 ◽  
Author(s):  
RV Baudinette ◽  
P Gill ◽  
M O'driscoll

Rates of oxygen consumption and means of augmenting the resultant heat production were studied in the little penguin, Eudyptula minor. Metabolic rates were lower than those predicted for a 1-kg bird, but shivering and an energy response to feeding were both present. The latter effect was independent of ambient temperatures between 2 deg and 22 deg C. The birds have limited ability to dissipate heat by evaporative water loss. About 40% of the total heat production was the maximum amount lost by this route. Cooling of expired respiratory gas provided an effective saving of heat and water. Moulting resulted in a 1.5-fold increase in metabolic rate but rates of evaporative water loss were reduced. The increase in heat production is correlated with increased thermal conductance across the body surface, as new feathers are synthesized, but body temperature is the same as in non-moulting penguins. The results suggest that increased heat loss when the birds are in water might be replaced by calorigenesis associated with the response to feeding, and by shivering, as well as by activity.


1997 ◽  
Vol 45 (2) ◽  
pp. 145 ◽  
Author(s):  
D. J. Hosken

Nyctophilus major is the largest member of its Australian-centred genus. Flow-through respirometry was used to investigate the thermal and metabolic physiology of adult N. major from south-western Australia. Oxygen consumption, carbon dioxide production, respiratory quotient, evaporative water loss and thermal conductance were measured at ambient temperatures of 5–40C. N. major was thermally labile and could be euthermic or torpid at low Ta. N. major entered into and spontaneously aroused from torpor at Tas as low as 5C, and became torpid at Tas as high as 23C. Like other temperate-zone Australian vespertilionid bats, some torpid N. major maintained a relatively high Tb at low Ta. Body mass and the duration of captivity had no detectable effect on the thermal responses of bats. The basal metabolic rate (BMR) of N. major was 85% of predicted, and falls within the the range of mass-specific BMRs reported for vespertilionid bats. While mean torpid á VO2 was reasonably high, torpor still facilitates substantial metabolic savings. However, because of the high á VO2 , N. major may not be able to remain torpid for more than about 60 days, relying solely on fat reserves. The evaporative water loss (EWL) of euthermic and torpid N. major was also high, although EWL during torpor was reduced compared with euthermy. Wet conductance was lower than predicted and probably relates to the solitary, tree-roosting habits of N. major. As has been reported for other bats, conductance values during torpor were lower than those during euthermy, but when torpid bats maintained a large ( Tb – Ta) differential at low Ta or became torpid at relatively high Ta , conductance values approached euthermic levels.


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