Phenotypic flexibility in heat production and heat loss in response to thermal and hydric acclimation in the zebra finch, a small arid-zone passerine

Abstract

To maintain constant body temperature (Tb) over a wide range of ambient temperatures (Ta) endothermic animals require large amounts of energy and water. In hot environments, the main threat to endothermic homeotherms is insufficient water to supply that necessary for thermoregulation. We investigated flexible adjustment of traits related to thermoregulation and water conservation during acclimation to hot conditions or restricted water availability, or both, in the zebra finch, Taeniopygia guttata a small arid-zone passerine. Using indirect calorimetry, we measured changes in whole animal metabolic rate (MR), evaporative heat loss (EHL) and Tb before and after acclimation to 23 or 40 °C, with different availability of water. Additionally, we quantified changes in partitioning of EHL into respiratory and cutaneous avenues in birds exposed to 25 and 40 °C. In response to heat and water restriction zebra finches decreased MR, which together with unchanged EHL resulted in increased efficiency of evaporative heat loss. This facilitated more precise Tb regulation in heat-acclimated birds. Acclimation temperature and water availability had no effect on the partitioning of EHL into cutaneous or respiratory avenues. At 25 °C, cutaneous EHL accounted for ~ 60% of total EHL, while at 40 °C, its contribution decreased to ~ 20%. Consistent among-individual differences in MR and EHL suggest that these traits, provided that they are heritable, may be a subject to natural selection. We conclude that phenotypic flexibility in metabolic heat production associated with acclimation to hot, water-scarce conditions is crucial in response to changing environmental conditions, especially in the face of current and predicted climate change.

The thermoregulatory role of relative bill and leg surface areas in a Mediterranean population of Great tit (Parus major)

“…), which occasionally matched the onset of panting. This behavior was also observed in Zebra finch (Taeniopygia guttata) individuals inside metabolic chambers when exposed to 40°C, favoring an increase in cutaneous evaporative heat loss (CEWL;Wojciechowski et al, 2021). However, during the metabolic trials, neither T b nor behaviors were registered, impeding formal analyses to evaluate their possible effects on Great tit thermoregulation.…”

Evaporative Water Loss and Stopover Behavior in Three Passerine Bird Species During Autumn Migration

“…This could be an explanation for the observation in our study. In addition, different adaptations to optimize heat loss in arid conditions, such as the ability to tolerate high body temperatures during facultative hyperthermia (Tieleman and Williams, 1999;Smit et al, 2013Smit et al, , 2016Nilsson et al, 2016), the dependence on wing-drooping as alternative heat dissipation behavior (Smit et al, 2016;Wojciechowski et al, 2021) or the reduction of metabolic rate (Williams and Tieleman, 2005;Wojciechowski et al, 2021) may also influence the temperature of panting onset. These factors clearly indicate new avenues for further research investigating the response of different species to dehydrating conditions.…”

“…The proportion of CWL and RWL to total evaporative water loss (TEWL) varies among species, but it is generally around 50% at moderate T a 's (Wolf and Walsberg, 1996;Tieleman and Williams, 2002;Ro and Williams, 2010). When T a approaches or exceeds T b , birds increase both cutaneous and respiratory water loss, but the latter to a greater extent (Wolf and Walsberg, 1996;Tieleman and Williams, 2002;Wojciechowski et al, 2021). With the exception of Columbiforms (McKechnie and Wolf, 2004), respiratory water loss is the main avenue of water loss when a bird is exposed to heat stress (Wolf and Walsberg, 1996;Tieleman and Williams, 2002;Wojciechowski et al, 2021).…”

“…When T a approaches or exceeds T b , birds increase both cutaneous and respiratory water loss, but the latter to a greater extent (Wolf and Walsberg, 1996;Tieleman and Williams, 2002;Wojciechowski et al, 2021). With the exception of Columbiforms (McKechnie and Wolf, 2004), respiratory water loss is the main avenue of water loss when a bird is exposed to heat stress (Wolf and Walsberg, 1996;Tieleman and Williams, 2002;Wojciechowski et al, 2021). Birds experiencing high rates of TEWL may have difficulties to keep their body adequately hydrated while maintaining body temperature below critical hyperthermia (Webster, 1991).…”

“…CWL is reduced through a specific lipid composition of the skin's stratum corneum, which makes it less permeable to endogenous water (Tieleman and Williams, 2002;Haugen, 2003;Haugen et al, 2003;Muñoz-Garcia and Williams, 2011;Champagne et al, 2012). A reduction of RWL in desert birds as a mechanism of water conservation has been discussed (Williams and Tieleman, 2005) and was observed in zebra finches (Taeniopygia guttata) acclimated to limited water availability (Wojciechowski et al, 2021). However, in the Kalahari Desert, bird species relying on food as their only water source started panting at a higher temperature and have overall higher evaporative scope when compared with species that drink water (Smit et al, 2016;Czenze et al, 2020).…”