Cutaneous water evaporation—I. Its significance in heat-stressed birds

Birds in subtropical deserts face significant thermoregulatory challenges because environmental temperatures regularly exceed avian body temperature. To understand the differing susceptibility of desert birds to increasing temperatures, we examined thermoregulatory performance and estimated heat tolerance limits (HTLs) for three Sonoran Desert nesting bird species -Gambel's quail, mourning doves and white-winged doves. Using flow-through respirometry we measured daytime resting metabolism, evaporative water loss and real-time body temperature at air temperatures (T air ) from 30°C to 66°C. We found marked increases in resting metabolism at the upper critical temperature (T uc ), which was significantly lower in the quail (T air =41.1°C) than in both dove species (T air =45.9-46.5°C). Gambel's quail maintained low resting metabolic rates and low rates of evaporative water loss at their T uc (0.71 W and 1.20 g H 2 O h −1 , respectively), but were more sensitive to increasing air temperature, reaching their HTL at T air of 52°C. Mourning doves and white-winged doves maintained low resting metabolic rates (0.66 and 0.94 W), but higher rates of evaporative water loss (1.91 and 2.99 g H 2 O h −1 ) at their T uc and reached their HTL at T air of 58-60°C. Mass-specific evaporative water loss in white-winged doves (147 g) and mourning doves (104 g) was 45% and 30% greater, respectively, than the rate observed in Gambel's quail (161 g) at T air of 48°C. Higher rates of evaporation and higher T uc made the doves exceptionally heat tolerant, allowing them to maintain body temperatures at least 14°C below air temperatures as high as 60°C (140°F).

Section: Introductionmentioning

confidence: 63%

Avian thermoregulation in the heat: resting metabolism, evaporative cooling and heat tolerance in Sonoran Desert doves and quail

Smith

O'Neill

Gerson

et al. 2015

“…Models of cutaneous water movement are subject to uncertainties related to the phase state of water moving through epidermal tissues and the potential effects of hydration and temperature (Scheuplein and Blank, 1971;Mautz, 1982;Marder and Ben-Asher, 1983). Webster et al (1985) properly note that if liquid water moves into the superficial layers of the skin, water in the vapor phase might diffuse across a shorter pathway and, hence, reduced resistance.…”

Section: Water Permeation In Keratinsmentioning

confidence: 99%

Water relations of tetrapod integument

Lillywhite

2006

265

240

“…This reduction in CWL was associated with an increase in the proportion of more polar ceramides, and a decrease in the proportion of free fatty acids (Haugen et al, 2003a;Haugen et al, 2003b). However, the skin of some species of birds also plays a role in thermoregulation, at least when T a is high (Bernstein, 1971;Marder and Ben-Asher, 1983). So, when T a is favorable, desert birds should have minimal water loss through the skin, but when T a exceeds body temperature, CWL should be elevated.…”

Section: Introductionmentioning

confidence: 99%

Cutaneous water loss and sphingolipids in the stratum corneum of house sparrows,Passer domesticusL., from desert and mesic environments as determined by reversed phase high-performance liquid chromatography coupled with atmospheric pressure photospray ionization mass spectrometry

Muñoz‐Garcia

Brown³

et al. 2008

SUMMARYBecause cutaneous water loss (CWL) represents half of total water loss in birds, selection to reduce CWL may be strong in desert birds. We previously found that CWL of house sparrows from a desert population was about 25% lower than that of individuals from a mesic environment. The stratum corneum (SC), the outer layer of the epidermis, serves as the primary barrier to water vapor diffusion through the skin. The avian SC is formed by layers of corneocytes embedded in a lipid matrix consisting of cholesterol, free fatty acids and two classes of sphingolipids, ceramides and cerebrosides. The SC of birds also serves a thermoregulatory function; high rates of CWL keep body temperatures under lethal limits in episodes of heat stress.In this study, we used high-performance liquid chromatography coupled with atmospheric pressure photoionization-mass spectrometry (HPLC/APPI-MS) to identify and quantify over 200 sphingolipids in the SC of house sparrows from desert and mesic populations. Principal components analysis (PCA) led to the hypotheses that sphingolipids in the SC of desert sparrows have longer carbon chains in the fatty acid moiety and are more polar than those found in mesic sparrows. We also tested the association between principal components and CWL in both populations. Our study suggested that a reduction in CWL found in desert sparrows was, in part, the result of modifications in chain length and polarity of the sphingolipids, changes that apparently determine the interactions of the lipid molecules within the SC.