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Nowack J, Turbill C. Survivable hypothermia or torpor in a wild-living rat: rare insights broaden our understanding of endothermic physiology. J Comp Physiol B 2021; 192:183-192. [PMID: 34668054 PMCID: PMC8817056 DOI: 10.1007/s00360-021-01416-3] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2021] [Revised: 09/08/2021] [Accepted: 10/03/2021] [Indexed: 12/16/2022]
Abstract
Maintaining a high and stable body temperature as observed in endothermic mammals and birds is energetically costly. Thus, it is not surprising that we discover more and more heterothermic species that can reduce their energetic needs during energetic bottlenecks through the use of torpor. However, not all heterothermic animals use torpor on a regular basis. Torpor may also be important to an individual’s probability of survival, and hence fitness, when used infrequently. We here report the observation of a single, ~ 5.5 h long hypothermic bout with a decrease in body temperature by 12 °C in the native Australian bush rat (Rattus fuscipes). Our data suggest that bush rats are able to rewarm from a body temperature of 24 °C, albeit with a rewarming rate lower than that expected on the basis of their body mass. Heterothermy, i.e. the ability to withstand and overcome periods of reduced body temperature, is assumed to be an evolutionarily ancestral (plesiomorphic) trait. We thus argue that such rare hypothermic events in species that otherwise appear to be strictly homeothermic could be heterothermic rudiments, i.e. a less derived form of torpor with limited capacity for rewarming. Importantly, observations of rare and extreme thermoregulatory responses by wild animals are more likely to be discovered with long-term data sets and may not only provide valuable insight about the physiological capability of a population, but can also help us to understand the constraints and evolutionary pathways of different phenologies.
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Affiliation(s)
- Julia Nowack
- Hawkesbury Institute for the Environment and School of Science, Western Sydney University, Richmond, NSW, Australia. .,School of Biological and Environmental Sciences, Liverpool John Moores University, Byrom Street, Liverpool, L3 3AF, UK.
| | - Christopher Turbill
- Hawkesbury Institute for the Environment and School of Science, Western Sydney University, Richmond, NSW, Australia
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Nowack J, Levesque DL, Reher S, Dausmann KH. Variable Climates Lead to Varying Phenotypes: “Weird” Mammalian Torpor and Lessons From Non-Holarctic Species. Front Ecol Evol 2020. [DOI: 10.3389/fevo.2020.00060] [Citation(s) in RCA: 38] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
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Cortes PA, Bozinovic F, Blier PU. Mitochondrial phenotype during torpor: Modulation of mitochondrial electron transport system in the Chilean mouse-opossum Thylamys elegans. Comp Biochem Physiol A Mol Integr Physiol 2018; 221:7-14. [PMID: 29551753 DOI: 10.1016/j.cbpa.2017.12.014] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2017] [Revised: 11/30/2017] [Accepted: 12/08/2017] [Indexed: 12/20/2022]
Abstract
Mammalian torpor is a phenotype characterized by a controlled decline of metabolic rate, generally followed by a reduction in body temperature. During arousal from torpor, both metabolic rate and body temperature rapidly returns to resting levels. Metabolic rate reduction experienced by torpid animals is triggered by active suppression of mitochondrial respiration, which is rapidly reversed during rewarming process. In this study, we analyzed the changes in the maximal activity of key enzymes related to electron transport system (complexes I, III and IV) in six tissues of torpid, arousing and euthermic Chilean mouse-opossums (Thylamys elegans). We observed higher maximal activities of complexes I and IV during torpor in brain, heart and liver, the most metabolically active organs in mammals. On the contrary, higher enzymatic activities of complexes III were observed during torpor in kidneys and lungs. Moreover, skeletal muscle was the only tissue without significant differences among stages in all complexes evaluated, suggesting no modulation of oxidative capacities of electron transport system components in this thermogenic tissue. In overall, our data suggest that complexes I and IV activity plays a major role in initiation and maintenance of metabolic suppression during torpor in Chilean mouse-opossum, whereas improvement of oxidative capacities in complex III might be critical to sustain metabolic machinery in organs that remains metabolically active during torpor.
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Affiliation(s)
- Pablo A Cortes
- Escuela de Agronomía, Facultad de Ciencias, Universidad Mayor, Camino La Pirámide, 5750, Huechuraba, Chile; Departamento de Ecología, Center of Applied Ecology and Sustainability, Facultad de Ciencias Biológicas, Universidad Católica de Chile, Santiago 6513677, Chile.
| | - Francisco Bozinovic
- Departamento de Ecología, Center of Applied Ecology and Sustainability, Facultad de Ciencias Biológicas, Universidad Católica de Chile, Santiago 6513677, Chile
| | - Pierre U Blier
- Département de Biologie, Laboratoire de Physiologie Animale Intégrative, Université du Québec, Rimouski G5L 3A1, QC, Canada
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Genoud M, Isler K, Martin RD. Comparative analyses of basal rate of metabolism in mammals: data selection does matter. Biol Rev Camb Philos Soc 2017; 93:404-438. [PMID: 28752629 DOI: 10.1111/brv.12350] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2016] [Revised: 05/29/2017] [Accepted: 06/05/2017] [Indexed: 12/21/2022]
Abstract
Basal rate of metabolism (BMR) is a physiological parameter that should be measured under strictly defined experimental conditions. In comparative analyses among mammals BMR is widely used as an index of the intensity of the metabolic machinery or as a proxy for energy expenditure. Many databases with BMR values for mammals are available, but the criteria used to select metabolic data as BMR estimates have often varied and the potential effect of this variability has rarely been questioned. We provide a new, expanded BMR database reflecting compliance with standard criteria (resting, postabsorptive state; thermal neutrality; adult, non-reproductive status for females) and examine potential effects of differential selectivity on the results of comparative analyses. The database includes 1739 different entries for 817 species of mammals, compiled from the original sources. It provides information permitting assessment of the validity of each estimate and presents the value closest to a proper BMR for each entry. Using different selection criteria, several alternative data sets were extracted and used in comparative analyses of (i) the scaling of BMR to body mass and (ii) the relationship between brain mass and BMR. It was expected that results would be especially dependent on selection criteria with small sample sizes and with relatively weak relationships. Phylogenetically informed regression (phylogenetic generalized least squares, PGLS) was applied to the alternative data sets for several different clades (Mammalia, Eutheria, Metatheria, or individual orders). For Mammalia, a 'subsampling procedure' was also applied, in which random subsamples of different sample sizes were taken from each original data set and successively analysed. In each case, two data sets with identical sample size and species, but comprising BMR data with different degrees of reliability, were compared. Selection criteria had minor effects on scaling equations computed for large clades (Mammalia, Eutheria, Metatheria), although less-reliable estimates of BMR were generally about 12-20% larger than more-reliable ones. Larger effects were found with more-limited clades, such as sciuromorph rodents. For the relationship between BMR and brain mass the results of comparative analyses were found to depend strongly on the data set used, especially with more-limited, order-level clades. In fact, with small sample sizes (e.g. <100) results often appeared erratic. Subsampling revealed that sample size has a non-linear effect on the probability of a zero slope for a given relationship. Depending on the species included, results could differ dramatically, especially with small sample sizes. Overall, our findings indicate a need for due diligence when selecting BMR estimates and caution regarding results (even if seemingly significant) with small sample sizes.
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Affiliation(s)
- Michel Genoud
- Department of Ecology and Evolution, University of Lausanne, CH-1015, Lausanne, Switzerland.,Division of Conservation Biology, Institute of Ecology and Evolution, Department of Biology, University of Bern, CH-3012, Bern, Switzerland
| | - Karin Isler
- Department of Anthropology, University of Zürich-Irchel, CH-8057, Zürich, Switzerland
| | - Robert D Martin
- Integrative Research Center, The Field Museum, Chicago, IL, 60605-2496, U.S.A.,Institute of Evolutionary Medicine, University of Zürich-Irchel, CH-8057, Zürich, Switzerland
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Nowack J, Geiser F. Friends with benefits: the role of huddling in mixed groups of torpid and normothermic animals. ACTA ACUST UNITED AC 2015; 219:590-6. [PMID: 26685170 DOI: 10.1242/jeb.128926] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2015] [Accepted: 12/01/2015] [Indexed: 12/24/2022]
Abstract
Huddling and torpor are widely used for minimizing heat loss by mammals. Despite the questionable energetic benefits from social heterothermy of mixed groups of warm normothermic and cold torpid individuals, the heterothermic Australian sugar glider (Petaurus breviceps) rests in such groups during the cold season. To unravel why they might do so, we examined torpor expression of two sugar glider groups of four individuals each in outside enclosures during winter. We observed 79 torpor bouts during 50 days of observation and found that torpor bouts were longer and deeper when all individuals of a group entered torpor together, and therefore infer that they would have saved more energy in comparison to short and shallow solitary torpor bouts. However, all gliders of either group only expressed torpor uniformly in response to food restriction, whereas on most occasions at least one individual per group remained normothermic. Nevertheless, the presence of warm gliders in mixed groups also appears to be of energetic advantage for torpid individuals, because nest box temperature was negatively correlated with the number of torpid gliders, and normothermic individuals kept the nest temperature at a value closer to the threshold for thermoregulatory heat production during torpor. Our study suggests that mixed groups of torpid and normothermic individuals are observed when environmental conditions are adverse but food is available, leading to intermediate energy savings from torpor. However, under especially challenging conditions and when animals are starving, energy savings are maximized by uniform and pronounced expression of torpor.
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Affiliation(s)
- Julia Nowack
- Centre for Behavioural and Physiological Ecology, Zoology, University of New England, Armidale, New South Wales 2351, Australia
| | - Fritz Geiser
- Centre for Behavioural and Physiological Ecology, Zoology, University of New England, Armidale, New South Wales 2351, Australia
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Oelkrug R, Polymeropoulos ET, Jastroch M. Brown adipose tissue: physiological function and evolutionary significance. J Comp Physiol B 2015; 185:587-606. [PMID: 25966796 DOI: 10.1007/s00360-015-0907-7] [Citation(s) in RCA: 176] [Impact Index Per Article: 19.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2014] [Revised: 04/21/2015] [Accepted: 04/26/2015] [Indexed: 01/11/2023]
Abstract
In modern eutherian (placental) mammals, brown adipose tissue (BAT) evolved as a specialized thermogenic organ that is responsible for adaptive non-shivering thermogenesis (NST). For NST, energy metabolism of BAT mitochondria is increased by activation of uncoupling protein 1 (UCP1), which dissipates the proton motive force as heat. Despite the presence of UCP1 orthologues prior to the divergence of teleost fish and mammalian lineages, UCP1's significance for thermogenic adipose tissue emerged at later evolutionary stages. Recent studies on the presence of BAT in metatherians (marsupials) and eutherians of the afrotherian clade provide novel insights into the evolution of adaptive NST in mammals. In particular studies on the 'protoendothermic' lesser hedgehog tenrec (Afrotheria) suggest an evolutionary scenario linking BAT to the onset of eutherian endothermy. Here, we review the physiological function and distribution of BAT in an evolutionary context by focusing on the latest research on phylogenetically distinct species.
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Affiliation(s)
- R Oelkrug
- Department of Animal Physiology, Faculty of Biology, Philipps-Universität Marburg, Karl-von-Frisch Straße 8, 35043, Marburg, Germany,
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Affiliation(s)
- Julia Nowack
- Department of Animal Ecology and Conservation; Biocentre Grindel; University of Hamburg; Martin-Luther-King Platz 3 20146 Hamburg Germany
- Centre for Behavioural and Physiological Ecology, Zoology; University of New England; Armidale NSW 2351 Australia
| | - Kathrin H. Dausmann
- Department of Animal Ecology and Conservation; Biocentre Grindel; University of Hamburg; Martin-Luther-King Platz 3 20146 Hamburg Germany
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Stawski C, Koteja P, Sadowska ET, Jefimow M, Wojciechowski MS. Selection for high activity-related aerobic metabolism does not alter the capacity of non-shivering thermogenesis in bank voles. Comp Biochem Physiol A Mol Integr Physiol 2014; 180:51-6. [PMID: 25446149 DOI: 10.1016/j.cbpa.2014.11.003] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2014] [Revised: 10/31/2014] [Accepted: 11/02/2014] [Indexed: 12/22/2022]
Abstract
An intriguing question is how the capacity of non-shivering thermogenesis (NST)-a special mechanism supporting endothermic thermoregulation in mammals-is affected by selection for high exercise metabolism. It has been proposed that high NST could be a mechanism to compensate for a low basal production of heat. On the other hand, high basal or activity metabolism is associated with physiological characteristics such as high performance of the circulatory system, which are also required for achieving a high NST. Here we tested whether selection for high aerobic exercise performance, which correlates with an increased basal metabolic rate, led to a correlated evolution of maximum and facultative NST. Therefore, we measured the NST of bank voles, Myodes (= Clethrionomys) glareolus, from lines selected for 13-14 generations (n=46) for high aerobic metabolism achieved during swimming and from unselected, control lines (n=46). Open-flow respirometry was used to measure the rate of oxygen consumption (V(·)O2) in anesthetized bank voles injected with noradrenaline (NA). After adjusting for body mass, maximum NST (maximum V(·)O2 recorded after injection of NA) did not differ between the selected (2.38±0.08 mLO2min(-1)) and control lines (2.36±0.08 mLO2min(-1); P=0.891). Facultative NST (= maximum NST minus resting metabolic rate of anesthetized animals) did not differ between the selected (1.49±0.07 mLO2min(-1)) and control lines (1.50±0.07 mLO2min(-1); P=0.985), either. Therefore, our results suggest that NST capacity is not strongly linked to maximum activity-related aerobic metabolic rate.
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Affiliation(s)
- Clare Stawski
- Institute of Environmental Sciences, Jagiellonian University, ul. Gronostajowa 7, 30-387 Kraków, Poland.
| | - Paweł Koteja
- Institute of Environmental Sciences, Jagiellonian University, ul. Gronostajowa 7, 30-387 Kraków, Poland
| | - Edyta T Sadowska
- Institute of Environmental Sciences, Jagiellonian University, ul. Gronostajowa 7, 30-387 Kraków, Poland
| | - Małgorzata Jefimow
- Department of Animal Physiology, Nicolaus Copernicus University, ul. Lwowska 1, 87-100 Toruń, Poland
| | - Michał S Wojciechowski
- Department of Animal Physiology, Nicolaus Copernicus University, ul. Lwowska 1, 87-100 Toruń, Poland
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Cortés PA, Franco M, Moreno-Gómez FN, Barrientos K, Nespolo RF. Thermoregulatory capacities and torpor in the South American marsupial, Dromiciops gliroides. J Therm Biol 2014; 45:1-8. [DOI: 10.1016/j.jtherbio.2014.07.003] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2014] [Revised: 07/03/2014] [Accepted: 07/03/2014] [Indexed: 10/25/2022]
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Affiliation(s)
- K. H. Dausmann
- Department of Animal Ecology and Conservation, Biocentre Grindel; University of Hamburg; Hamburg Germany
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Stead N. AROUSAL FROM TORPOR: A BUSHBABY'S METHODS. J Exp Biol 2013. [DOI: 10.1242/jeb.094615] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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