5 research outputs found
Solar Radiation during Rewarming from Torpor in Elephant Shrews: Supplementation or Substitution of Endogenous Heat Production?
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.The National
Research Foundation and the University of Pretoria.http://www.plosone.orgam201
Global patterns of seasonal acclimatization in avian resting metabolic rates
The adjustment of resting metabolic rates represents an important component of avian
seasonal acclimatization, with recent studies revealing substantial differences between
summer and winter in birds from a wide range of latitudes. We compared seasonal
variation in basal metabolic rate (BMR) and summit metabolism (Msum) between
temperate and tropical/subtropical latitudes, and examined correlations with latitude
and temperature. The direction and magnitude of seasonal adjustments in BMR are
broadly related to temperature and latitude, but are significantly more variable among
tropical and subtropical species compared to those inhabiting temperate zones. Winter
adjustments in BMR among subtropical species, when expressed relative to summer values, range from decreases of approximately 35 % to increases of more than 60 %,
whereas the majority of temperate-zone species show increases in BMR during
winter. Relatively few seasonal Msum data exist for tropical/subtropical species, but
those that are available involve responses ranging from winter decreases to increases
of similar magnitude to those characteristic of many temperate-zone species. Recent
studies also highlight the substantial variation in seasonal adjustments that may occur
within species, and reiterate the need for further investigations of the relative roles of
environmental variables such as temperature and food availability as determinants of
seasonal metabolic variation.http://link.springer.com/journal/103362016-12-30hb201