Evaporative water loss, relative water economy and evaporative partitioning of a heterothermic marsupial, the monito del monte (Dromiciops gliroides)

Abstract

SUMMARYWe examine here evaporative water loss, economy and partitioning at ambient temperatures from 14 to 33°C for the monito del monte (Dromiciops gliroides), a microbiotheriid marsupial found only in temperate rainforests of Chile. The monitoʼs standard evaporative water loss (2.58mgg -1 h -1 at 30°C) was typical for a marsupial of its body mass and phylogenetic position. Evaporative water loss was independent of air temperature below thermoneutrality, but enhanced evaporative water loss and hyperthermia were the primary thermal responses above the thermoneutral zone. Non-invasive partitioning of total evaporative water loss indicated that respiratory loss accounted for 59-77% of the total, with no change in respiratory loss with ambient temperature, but a small change in cutaneous loss below thermoneutrality and an increase in cutaneous loss in and above thermoneutrality. Relative water economy (metabolic water production/evaporative water loss) increased at low ambient temperatures, with a point of relative water economy of 15.4°C. Thermolability had little effect on relative water economy, but conferred substantial energy savings at low ambient temperatures. Torpor reduced total evaporative water loss to as little as 21% of normothermic values, but relative water economy during torpor was poor even at low ambient temperatures because of the relatively greater reduction in metabolic water production than in evaporative water loss. The poor water economy of the monito during torpor suggests that negative water balance may explain why hibernators periodically arouse to normothermia, to obtain water by drinking or via an improved water economy.

Physiological regulation of evaporative water loss in endotherms: is the little red kaluta (Dasykaluta rosamondae) an exception or the rule?

“…This non-exponential effect of T a on EWL below thermoneutrality is generally attributed to the counteracting effects of T a on respiratory and cutaneous EWL. Thermoregulatory adjustments in MR increase respiratory ventilation and EWL at low T a , which counterbalances the expected decrease in cutaneous EWL [24,25]. In the light of our findings for EWL constancy at low RH, an alternative interpretation of this EWL constancy at low T a is that EWL is acutely regulated over this T a range.…”

“…2] and a higher EWL/Dwvp at 358C compared with 258C and 308C (this study; figure 2). At T a below TNZ, EWL of endotherms is often constant or even decreases with increasing T a [24,25], rather than increasing exponentially with T a as would be predicted (by the physical effect). Kaluta are no exception.…”

“…by modification of skin lipids [30][31][32], and/or reduced respiratory EWL, e.g. by lowered expired air temperature by nasal counter-current heat and water exchange [25,[33][34][35][36].…”

Ecological consequences of temperature regulation: Why might the mountain pygmy possumBurramys parvusneed to hibernate near underground streams?

“…The ratio of these, relative water economy (relative water economy = metabolic water production/evaporative water loss), is therefore an index of the state of water balance for a torpid mammal. 16 Many small mammals, even tropical and mesic species, have a favorable relative water economy (i.e., they make more metabolic water than they lose by evaporation) when euthermic at moderate to low ambient temperatures. [23][24][25][26] However during torpor, their metabolic rate (and therefore metabolic water production) decreases proportionally more than their evaporative water loss, and so the relative water economy becomes more unfavorable, and water balance is typically negative.…”

“…[23][24][25][26] However during torpor, their metabolic rate (and therefore metabolic water production) decreases proportionally more than their evaporative water loss, and so the relative water economy becomes more unfavorable, and water balance is typically negative. 16,[27][28][29][30] Water loss equivalent to about 5% body mass appears to be a critical limit requiring arousal from torpor, 31 and so it is likely that hibernating mammals reaching this limit must arouse to drink. For another hibernating marsupial, the monito del monte (Dromiciops gliroides), rates of mass loss calculated from RWE during torpor correlated with observed periodicity of arousals in the field, 16 indicating that maintenance of water balance may indeed be an important function of periodic arousals during hibernation.…”