Avian thermoregulation in the heat: evaporative cooling in five Australian passerines reveals within-order biogeographic variation in heat tolerance
| Autor: | Todd J. McWhorter, Eric Krabbe Smith, William A. Talbot, Blair O. Wolf, Andrew E. McKechnie, Alexander R. Gerson |
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| Rok vydání: | 2016 |
| Předmět: |
030110 physiology
0301 basic medicine Thermotolerance Hot Temperature Physiology Aquatic Science Pomatostomus ruficeps Songbirds 03 medical and health sciences Animal science Animals Molecular Biology Ecology Evolution Behavior and Systematics Acanthagenys Grey butcherbird biology Ecology Australia Lichenostomus ornatus Thermoregulation biology.organism_classification Honeyeater Insect Science Basal metabolic rate Animal Science and Zoology Evaporative cooler Body Temperature Regulation |
| Zdroj: | The Journal of experimental biology. 220(Pt 13) |
| ISSN: | 1477-9145 |
| Popis: | Evaporative heat loss pathways vary among avian orders, but the extent to which evaporative cooling capacity and heat tolerance vary within orders remains unclear. We quantified the upper limits to thermoregulation under extremely hot conditions in five Australian passerines: yellow-plumed honeyeater ( Lichenostomus ornatus ; ∼17 g), spiny-cheeked honeyeater ( Acanthagenys rufogularis ; ∼42 g), chestnut-crowned babbler ( Pomatostomus ruficeps ; ∼52 g), grey butcherbird ( Cracticus torquatus ; ∼86 g) and apostlebird ( Struthidea cinerea ; ∼118 g). At air temperatures ( T a ) exceeding body temperature ( T b ), all five species showed increases in T b to maximum values around 44–45°C, accompanied by rapid increases in resting metabolic rate above clearly defined upper critical limits of thermoneutrality and increases in evaporative water loss (EWL) to levels equivalent to 670–860% of baseline rates at thermoneutral T a . Maximum cooling capacity, quantified as the fraction of metabolic heat production dissipated evaporatively, ranged from 1.20 to 2.17, consistent with the known range for passerines, and well below the corresponding ranges for columbids and caprimulgids. Heat tolerance limit (HTL, the maximum T a tolerated) scaled positively with body mass, varying from 46°C in yellow-plumed honeyeaters to 52°C in a single apostlebird, but was lower than that of three southern African ploceid passerines investigated previously. We argue this difference is functionally linked to a smaller scope for increases in EWL above baseline levels. Our data reiterate the reliance of passerines in general on respiratory evaporative heat loss via panting, but also reveal substantial within-order variation in heat tolerance and evaporative cooling capacity. |
| Databáze: | OpenAIRE |
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