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

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.

Download Full-text

Water turnover and the northern range of the koala (Phascolarctos cinereus).

Australian Mammalogy ◽

10.1071/am07010 ◽

2007 ◽

Vol 29 (1) ◽

pp. 85 ◽

Cited By ~ 14

Author(s):

I.D. Clifton ◽

W.A.H. Ellis ◽

A. Melzer ◽

G. Tucker

Keyword(s):

Relative Humidity ◽

Moisture Content ◽

Water Loss ◽

Evaporative Water Loss ◽

Water Requirements ◽

Water Turnover ◽

Evaporative Water ◽

Phascolarctos Cinereus ◽

Energy Demands ◽

Cooling Mechanism

Water turnover for koalas is positively correlated with the moisture content of selected trees suggesting that browse choice was driven by water requirements in summer but energy demands in winter. We compared the distribution of the koala to relative humidity and found that the bioregional delineation of the koala?s range corresponds closely to regions experiencing an average 9am relative humidity of less than 80% in February. This indicates that the northern coastal distribution of the koala may be limited by respiratory evaporative water loss as a cooling mechanism.

Download Full-text

Temperature regulation and evaporative water loss in the brush-tailed possum Trichosurus vulpecula

Comparative Biochemistry and Physiology ◽

10.1016/0010-406x(69)91353-x ◽

1969 ◽

Vol 28 (1) ◽

pp. 401-407 ◽

Cited By ~ 28

Author(s):

Terence J. Dawson

Keyword(s):

Temperature Regulation ◽

Water Loss ◽

Evaporative Water Loss ◽

Trichosurus Vulpecula ◽

Evaporative Water

Download Full-text

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

Biology Letters ◽

10.1098/rsbl.2017.0537 ◽

2017 ◽

Vol 13 (11) ◽

pp. 20170537 ◽

Cited By ~ 1

Author(s):

Christine Elizabeth Cooper ◽

Philip Carew Withers

Keyword(s):

Relative Humidity ◽

Water Loss ◽

Physiological Role ◽

Vapour Pressure Deficit ◽

Evaporative Water Loss ◽

Regulatory Control ◽

Water Vapour Pressure ◽

Evaporative Water ◽

Ambient Temperatures

‘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.

Download Full-text