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Reaction norms for heat tolerance and evaporative cooling capacity do not vary across a climatic gradient in a passerine bird.

Abstract

There is increasing evidence for considerable phenotypic flexibility in endotherm thermal physiology, a phenomenon with far-reaching implications for the evolution of traits related to heat tolerance. Numerous studies have documented intraspecific variation in avian thermoregulatory traits, but few have revealed the shapes of thermoregulatory reaction norms or how these might vary among populations. We investigated phenotypic flexibility in the ability of a model Afrotropical passerine bird (the white-browed sparrow-weaver, Plocepasser mahali) to handle high air temperatures (Ta). We allocated birds from three sites varying by ~ 11 °C in mean daily summer maximum Ta to three acclimation temperature (Taccl) treatments (daytime Taccl ≈ 30 °C, 36 °C or 42 °C respectively; n ≈ 10 per site per Taccl). After an acclimation period of 30 days, heat tolerance and evaporative cooling capacity was quantified by exposing birds to progressively higher Ta until they approached severe hyperthermia (body temperature [Tb] = 44.5 °C; Ta range: 38-54 °C). We measured metabolic rate and evaporative water loss using open flow-through respirometry, and Tb using temperature-sensitive passive-integrated transponder tags. Hyperthermia threshold Ta (Ta,HT) was significantly higher and Tb significantly lower in birds acclimated to the hottest Taccl compared to those from milder acclimation treatments. Population (i.e., site of capture) was not a significant predictor of any thermoregulatory variables or hyperthermia threshold Ta (Ta,HT) after acclimation, revealing that the shape of reaction norms for heat tolerance and evaporative cooling capacity does not vary among these three populations.

Authors+Show Affiliations

DST-NRF Centre of Excellence at the FitzPatrick Institute, Department of Zoology and Entomology, University of Pretoria, Pretoria 0002, South Africa.DST-NRF Centre of Excellence at the FitzPatrick Institute, Department of Zoology and Entomology, University of Pretoria, Pretoria 0002, South Africa; South African Research Chair in Conservation Physiology, National Zoological Garden, South African National Biodiversity Institute, Pretoria, South Africa. Electronic address: aemckechnie@up.ac.za.

Pub Type(s)

Journal Article

Language

eng

PubMed ID

31278988

Citation

Noakes, Matthew J., and Andrew E. McKechnie. "Reaction Norms for Heat Tolerance and Evaporative Cooling Capacity Do Not Vary Across a Climatic Gradient in a Passerine Bird." Comparative Biochemistry and Physiology. Part A, Molecular & Integrative Physiology, vol. 236, 2019, p. 110522.
Noakes MJ, McKechnie AE. Reaction norms for heat tolerance and evaporative cooling capacity do not vary across a climatic gradient in a passerine bird. Comp Biochem Physiol, Part A Mol Integr Physiol. 2019;236:110522.
Noakes, M. J., & McKechnie, A. E. (2019). Reaction norms for heat tolerance and evaporative cooling capacity do not vary across a climatic gradient in a passerine bird. Comparative Biochemistry and Physiology. Part A, Molecular & Integrative Physiology, 236, p. 110522. doi:10.1016/j.cbpa.2019.06.022.
Noakes MJ, McKechnie AE. Reaction Norms for Heat Tolerance and Evaporative Cooling Capacity Do Not Vary Across a Climatic Gradient in a Passerine Bird. Comp Biochem Physiol, Part A Mol Integr Physiol. 2019;236:110522. PubMed PMID: 31278988.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Reaction norms for heat tolerance and evaporative cooling capacity do not vary across a climatic gradient in a passerine bird. AU - Noakes,Matthew J, AU - McKechnie,Andrew E, Y1 - 2019/07/03/ PY - 2019/04/22/received PY - 2019/06/02/revised PY - 2019/06/27/accepted PY - 2019/7/7/pubmed PY - 2019/7/7/medline PY - 2019/7/7/entrez KW - Acclimation KW - Arid-zone birds KW - Evaporative water loss KW - Heat stress, hyperthermia KW - Heat tolerance KW - Passerine KW - Phenotypic flexibility KW - Reaction norms SP - 110522 EP - 110522 JF - Comparative biochemistry and physiology. Part A, Molecular & integrative physiology JO - Comp. Biochem. Physiol., Part A Mol. Integr. Physiol. VL - 236 N2 - There is increasing evidence for considerable phenotypic flexibility in endotherm thermal physiology, a phenomenon with far-reaching implications for the evolution of traits related to heat tolerance. Numerous studies have documented intraspecific variation in avian thermoregulatory traits, but few have revealed the shapes of thermoregulatory reaction norms or how these might vary among populations. We investigated phenotypic flexibility in the ability of a model Afrotropical passerine bird (the white-browed sparrow-weaver, Plocepasser mahali) to handle high air temperatures (Ta). We allocated birds from three sites varying by ~ 11 °C in mean daily summer maximum Ta to three acclimation temperature (Taccl) treatments (daytime Taccl ≈ 30 °C, 36 °C or 42 °C respectively; n ≈ 10 per site per Taccl). After an acclimation period of 30 days, heat tolerance and evaporative cooling capacity was quantified by exposing birds to progressively higher Ta until they approached severe hyperthermia (body temperature [Tb] = 44.5 °C; Ta range: 38-54 °C). We measured metabolic rate and evaporative water loss using open flow-through respirometry, and Tb using temperature-sensitive passive-integrated transponder tags. Hyperthermia threshold Ta (Ta,HT) was significantly higher and Tb significantly lower in birds acclimated to the hottest Taccl compared to those from milder acclimation treatments. Population (i.e., site of capture) was not a significant predictor of any thermoregulatory variables or hyperthermia threshold Ta (Ta,HT) after acclimation, revealing that the shape of reaction norms for heat tolerance and evaporative cooling capacity does not vary among these three populations. SN - 1531-4332 UR - https://www.unboundmedicine.com/medline/citation/31278988/Reaction_norms_for_heat_tolerance_and_evaporative_cooling_capacity_do_not_vary_across_a_climatic_gradient_in_a_passerine_bird_ L2 - https://linkinghub.elsevier.com/retrieve/pii/S1095-6433(19)30278-8 DB - PRIME DP - Unbound Medicine ER -