Physiological responses of a rodent to heliox reveal constancy of evaporative water loss under perturbing environmental conditions

Abstract

Total evaporative water loss of endotherms is assumed to be determined essentially by biophysics, at least at temperatures below thermoneutrality, with evaporative water loss determined by the water vapor deficit between the animal and the ambient air. We present here evidence, based on the first measurements of evaporative water loss for a small mammal in heliox, that mammals may have a previously unappreciated ability to maintain acute constancy of total evaporative water loss under perturbing environmental conditions. Thermoregulatory responses of ash-grey mice (Pseudomys albocinereus) to heliox were as expected, with changes in metabolic rate, conductance, and respiratory ventilation consistent with maintaining constancy of body temperature under conditions of enhanced heat loss. However, evaporative water loss did not increase in heliox. This is despite our confirmation of the physical effect that heliox augments evaporation from nonliving surfaces, which should increase cutaneous water loss, and increases minute volume of live ash-grey mice in heliox to accommodate their elevated metabolic rate, which should increase respiratory water loss. Therefore, mice had not only a thermoregulatory but also a hygroregulatory response to heliox. We interpret these results as evidence that ash-grey mice can acutely control their evaporative water loss under perturbing environmental conditions and suggest that hygroregulation at and below thermoneutrality is an important aspect of the physiology of at least some small mammals.

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

“…The generally accepted physical model for insensible EWL is that Dwvp is the driving force (e.g. [5][6][7][8]19,34]), predicting that EWL/Dwvp is independent of RH (slope ¼ 0) and so a slope = 0 implies some form of EWL regulation. To examine the hypothesis that EWL/Dwvp is independent of RH, it is straightforward to statistically determine if the slope of the function of EWL/Dwvp versus RH ¼ 0, but it is not so straightforward to calculate EWL/Dwvp.…”

Respiration of thermogenic inflorescences of skunk cabbage Symplocarpus renifolius in heliox

“…The 1.4‐fold effect of heliox in S. renifolius is the same as the 1.4‐fold increase in hairless mice Mus musculus (Rosenmann & Morrison, ). Conductance increases relatively more in mammals that are more highly insulated, for example 1.6‐fold in ash‐grey mice Pseudomys albocinereus (Cooper & Withers, ), and 2.3‐fold in wild, highland mice M. musculus (Rosenmann & Morrison, ).…”

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

“…The specific physiological role of insensible EWL control is unknown. One hypothesis is that maintaining EWL constant over a range of DWVP simplifies thermoregulation [5,6]. Changes in EWL in response to a changing DWVP will modify evaporative heat loss (EHL), requiring a regulatory adjustment of heat production if T b is to remain constant.…”