Temperature regulation and metabolic rhythms in populations of the house sparrow, Passer domesticus

Intraspecific variation in avian thermoregulatory responses to heat stress has received little attention, despite increasing evidence that endothermic animals show considerable physiological variation among populations. We investigated seasonal (summer versus winter) variation in heat tolerance and evaporative cooling in an Afrotropical ploceid passerine, the white-browed sparrow-weaver (Plocepasser mahali; ∼47 g) at three sites along a climatic gradient with more than 10°C variation in mid-summer maximum air temperature (T a ). We measured resting metabolic rate (RMR) and total evaporative water loss (TEWL) using open flow-through respirometry, and core body temperature (T b ) using passive integrated transponder tags. Sparrow-weavers were exposed to a ramped profile of progressively higher T a between 30 and 52°C to elicit maximum evaporative cooling capacity (N=10 per site per season); the maximum T a birds tolerated before the onset of severe hyperthermia (T b ≈44°C) was considered to be their hyperthermia threshold T a (T a,HT ). Our data reveal significant seasonal acclimatisation of heat tolerance, with a desert population of sparrow-weavers reaching significantly higher T a in summer (49.5± 1.4°C, i.e. higher T a,HT ) than in winter (46.8±0.9°C), reflecting enhanced evaporative cooling during summer. Moreover, desert sparrow-weavers had significantly higher heat tolerance and evaporative cooling capacity during summer compared with populations from more mesic sites (T a,HT =47.3±1.5 and 47.6±1.3°C). A better understanding of the contributions of local adaptation versus phenotypic plasticity to intraspecific variation in avian heat tolerance and evaporative cooling capacity is needed for modelling species' responses to changing climates.

Section: Discussionmentioning

confidence: 83%

Seasonal and geographical variation in heat tolerance and evaporative cooling capacity in a passerine bird

Noakes

Wolf

McKechnie

2016

“…We injected birds immediately before placing them into the metabolic chamber. We maintained flow rates of dry, CO 2 -free air at 290mlmin −1 and kept the chamber temperature at 30°C, which is within the thermal neutral zone for house sparrows (Arens and Cooper, 2005;Hudson and Kimzey, 1966), throughout the RMR trials. We kept birds within the metabolic chambers overnight for ~12h.…”

Section: Resting Metabolic Ratementioning

confidence: 99%

Activation of the immune system incurs energetic costs but has no effect on the thermogenic performance of house sparrows during acute cold challenge

King

Swanson

2013

SUMMARYTrade-offs between the immune system and other condition-dependent life-history traits (reproduction, predator avoidance and somatic growth) have been well documented in both birds and mammals. However, no studies have examined the impact of immune activation on thermoregulatory performance during acute cold exposure. Because of their high surface-area-to-volume ratios, small birds incur high energetic costs associated with thermoregulation during cold exposure. Consequently, we predicted that the immune system and the thermoregulatory system would compete for energetic resources. To test this, we immunologically challenged adult house sparrows (Passer domesticus) with 5mgkg -1 of lipopolysaccharide (LPS) to induce an acute phase response and measured both resting (RMR; minimum metabolic rate) and summit (M sum ; maximal metabolic rate during cold exposure) metabolic rates. We found that birds injected with LPS had significantly higher RMR and M sum than birds injected with phosphate-buffered saline, indicating that LPS-treated birds were able to support the cost of both immune activation and thermoregulation under conditions eliciting maximal thermogenic performance. These results suggest that, in the absence of a pathogen, birds that experience short-term activation of the immune system have higher energetic costs during cold exposure, but immune activation does not compromise maximum thermoregulatory performance.

“…We controlled the temperature of the air in the chamber using a Neslab circulating water bath (model RTE-140) set at 30.0°C, a temperature within the thermoneutral zone of sparrows (Hudson and Kimzey, 1966). Sparrows stood on a wire mesh platform over a layer of mineral oil that trapped feces, eliminating them as a source of water in our measurements.…”

Section: Measurement Of Metabolic Rate and Evaporative Water Lossesmentioning

confidence: 99%

Cutaneous water loss and lipids of the stratum corneum in house sparrowsPasser domesticusfrom arid and mesic environments

Muñoz‐Garcia¹,

Williams²

2005

·SC·dry·mass in Ohio), and a lower percentage of cholesterol (4.1±3.6% in Saudi Arabia; 5.4±2.5% in Ohio) in their SC.Although CWL was lower in sparrows from Arabia, and lipid composition of their SC differed, we could not detect differences between rates of water loss through non-living skin attached to glass vials (46.0±15.7·mg·H 2 O·cm -2 ·day -1 for sparrows in Saudi Arabia; 45.8±27.2·mg·H 2 O·cm -2 ·day -1 for sparrows in Ohio). These results suggest that biological control mechanisms interact with layers of lipids in the stratum corneum to adjust CWL to the environment.