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Solar radiation during rewarming from torpor in elephant shrews: supplementation or substitution of endogenous heat production?

Thompson ML, Mzilikazi N, Bennett NC, McKechnie AE - PLoS ONE (2015)

Bottom Line: Many small mammals bask in the sun during rewarming from heterothermy, but the implications of this behaviour for their energy balance remain little understood.To address this question, we examined patterns of torpor and rewarming rates in eastern rock elephant shrews (Elephantulus myurus) housed in outdoor cages with access to either natural levels of solar radiation or levels that were experimentally reduced by means of shade cloth.BMR differed significantly between individuals experiencing natural levels of solar radiation and conspecifics experiencing approximately 20% of natural levels, but no between-treatment difference was evident for NST capacity or Msum.

View Article: PubMed Central - PubMed

Affiliation: Mammal Research Institute, Department of Zoology and Entomology, University of Pretoria, Private Bag X20, Hatfield 0028, South Africa.

ABSTRACT
Many small mammals bask in the sun during rewarming from heterothermy, but the implications of this behaviour for their energy balance remain little understood. Specifically, it remains unclear whether solar radiation supplements endogenous metabolic thermogenesis (i.e., rewarming occurs through the additive effects of internally-produced and external heat), or whether solar radiation reduces the energy required to rewarm by substituting (i.e, replacing) metabolic heat production. To address this question, we examined patterns of torpor and rewarming rates in eastern rock elephant shrews (Elephantulus myurus) housed in outdoor cages with access to either natural levels of solar radiation or levels that were experimentally reduced by means of shade cloth. We also tested whether acclimation to solar radiation availability was manifested via phenotypic flexibility in basal metabolic rate (BMR), non-shivering thermogenesis (NST) capacity and/or summit metabolism (Msum). Rewarming rates varied significantly among treatments, with elephant shrews experiencing natural solar radiation levels rewarming faster than conspecifics experiencing solar radiation levels equivalent to approximately 20% or 40% of natural levels. BMR differed significantly between individuals experiencing natural levels of solar radiation and conspecifics experiencing approximately 20% of natural levels, but no between-treatment difference was evident for NST capacity or Msum. The positive relationship between solar radiation availability and rewarming rate, together with the absence of acclimation in maximum non-shivering and total heat production capacities, suggests that under the conditions of this study solar radiation supplemented rather than substituted metabolic thermogenesis as a source of heat during rewarming from heterothermy.

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Overall mean heterothermy index [30].Eastern rock elephant shrews (Elephantulus myurus) housed in outdoor cages with exposure to natural (100%) or experimentally reduced (approximately 20% or 40%) levels of solar radiation.
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pone.0120442.g003: Overall mean heterothermy index [30].Eastern rock elephant shrews (Elephantulus myurus) housed in outdoor cages with exposure to natural (100%) or experimentally reduced (approximately 20% or 40%) levels of solar radiation.

Mentions: HI values varied significantly among treatments (GLMM, t = 2.56, P = 0.01), with HI values of 9.43 ± 4.69°C, 10.89 ± 4.49°C and 11.65 ± 4.38°C for the deep shade, partial shade and full sun treatments, respectively (Fig. 3). Significant differences existed between full sun and deep shade treatments (Tukey HSD, P = 0.012) as well as between partial shade and deep shade (Tukey HSD, P = 0.015).


Solar radiation during rewarming from torpor in elephant shrews: supplementation or substitution of endogenous heat production?

Thompson ML, Mzilikazi N, Bennett NC, McKechnie AE - PLoS ONE (2015)

Overall mean heterothermy index [30].Eastern rock elephant shrews (Elephantulus myurus) housed in outdoor cages with exposure to natural (100%) or experimentally reduced (approximately 20% or 40%) levels of solar radiation.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4390352&req=5

pone.0120442.g003: Overall mean heterothermy index [30].Eastern rock elephant shrews (Elephantulus myurus) housed in outdoor cages with exposure to natural (100%) or experimentally reduced (approximately 20% or 40%) levels of solar radiation.
Mentions: HI values varied significantly among treatments (GLMM, t = 2.56, P = 0.01), with HI values of 9.43 ± 4.69°C, 10.89 ± 4.49°C and 11.65 ± 4.38°C for the deep shade, partial shade and full sun treatments, respectively (Fig. 3). Significant differences existed between full sun and deep shade treatments (Tukey HSD, P = 0.012) as well as between partial shade and deep shade (Tukey HSD, P = 0.015).

Bottom Line: Many small mammals bask in the sun during rewarming from heterothermy, but the implications of this behaviour for their energy balance remain little understood.To address this question, we examined patterns of torpor and rewarming rates in eastern rock elephant shrews (Elephantulus myurus) housed in outdoor cages with access to either natural levels of solar radiation or levels that were experimentally reduced by means of shade cloth.BMR differed significantly between individuals experiencing natural levels of solar radiation and conspecifics experiencing approximately 20% of natural levels, but no between-treatment difference was evident for NST capacity or Msum.

View Article: PubMed Central - PubMed

Affiliation: Mammal Research Institute, Department of Zoology and Entomology, University of Pretoria, Private Bag X20, Hatfield 0028, South Africa.

ABSTRACT
Many small mammals bask in the sun during rewarming from heterothermy, but the implications of this behaviour for their energy balance remain little understood. Specifically, it remains unclear whether solar radiation supplements endogenous metabolic thermogenesis (i.e., rewarming occurs through the additive effects of internally-produced and external heat), or whether solar radiation reduces the energy required to rewarm by substituting (i.e, replacing) metabolic heat production. To address this question, we examined patterns of torpor and rewarming rates in eastern rock elephant shrews (Elephantulus myurus) housed in outdoor cages with access to either natural levels of solar radiation or levels that were experimentally reduced by means of shade cloth. We also tested whether acclimation to solar radiation availability was manifested via phenotypic flexibility in basal metabolic rate (BMR), non-shivering thermogenesis (NST) capacity and/or summit metabolism (Msum). Rewarming rates varied significantly among treatments, with elephant shrews experiencing natural solar radiation levels rewarming faster than conspecifics experiencing solar radiation levels equivalent to approximately 20% or 40% of natural levels. BMR differed significantly between individuals experiencing natural levels of solar radiation and conspecifics experiencing approximately 20% of natural levels, but no between-treatment difference was evident for NST capacity or Msum. The positive relationship between solar radiation availability and rewarming rate, together with the absence of acclimation in maximum non-shivering and total heat production capacities, suggests that under the conditions of this study solar radiation supplemented rather than substituted metabolic thermogenesis as a source of heat during rewarming from heterothermy.

Show MeSH
Related in: MedlinePlus