Lecture notes from various lectures in BIOL2018 adaptive physiology, temperature regulation. Covering: environmental and body temperature relationships, strategies in thermal regulation, temperatures' dominant effect on biological processes, ectotherms, thermoreception and dormancy
Temperature Regulation
Environmental and body temperature relationships
Heat exchange
Conduction – transfer of heat between two objects that are in physical contact
Convection – transfer of heat by the movement of a fluid (liquid or gas) against an
object
Radiation – radiated heat – heat you can sense without contact
Evaporation – liquid water changes to water vapour as a result of absorbing heat
from wet object - only way to transfer heat when environmental temperature
>=body temperature
Strategies for temperature homeostasis
Thermoconformers – don’t control internal state – therefore conform to the
environment – TB = TA
Thermoregulators – control internal state – therefore regulate against thermal
gradient – increase/decrease in heatloss/production as required – T B ≠ TA
Relative temperatures
Warmblood = 180C above ambient temperature
Cold blooded = ambient temperature
Can be confusing as leather back turtles are warm blooded whereas naked mole rat
is cold blooded
Changeable body temperature
Poikilothermic – derived from Greek Poikilos – changeable
Homeothermic – meaning stable body temp
In stable environment all have stable TB
Ectotherms – heat from environment
Endotherms – heat from metabolic processes
Conformers Vs Regulators
Conformers (ectotherms) – tolerate wide range of intetnal variation but narrow
environmental limits
Regulators (endotherms) – tolerate narrow range of internal variation, but wide
environmental limits
Both conformity and regulation are homeostatic mechanisms that allow for survival
in a changing environment
Acclimation and acclimitization allow animals to adapt further
Metabolic physiology
Endotherms can use metabolism to generate the heat they need to maintain a stbale
body temperature
Metabolic rate – one of the most commonly measured physiological variables, and is
a measure of the total energy used by an animal per unit time
Processes that use and generate energy:
Anabolic – assembly of simple compounds into complex molecules that are required
by organism – associated with growth and conversion of dietary components into
storage compounds
, Catabolic – breakdown of complex energy rich molecules into simpler molecules –
these reactions produce energy that can be used to perform work or is eventually
lost as heat
How is metabolism measured
Direct calorimetry – determined by measuring the amount of heat released by an
organism over a given period
Indirect calorimetry:
metabolic rate = (energy content of food – energy content of waste products)/time
doubly labelled water technique (2H218O) where 18O is lost through metabolic CO2 and
water loss but 2H is only lost through water loss
respirometry – directly measure oxygen consumption by the animal using a closed or
open system
Heat transfer and animal size
Body size and mass-specific metabolic rate (MR/m)
small animals – fast MR/m
large animals – slow MR/m
large animals heat up and cool down slowly
small animals heat up and cool down quickly
Metabolic rate scales with surface area
for homogenous objects surface area scales with mass to the power 0.67
log[S]=a+0.67log[m]
this is true for adult animals of a given species that maintain constant body
temperature
larger animals show disproportional thickening of bones and muscle resulting in a
relative decrease in S and a coefficient of 0.63 instead of 0.67
Isometry and allometry
Isometry – proportional scaling
Allometry – divergence in scaling
Body size and metabolic rate (MR)
Whole animal MR is a power function of body mass
MR = a x mb or log [MR] = log[a] + b log[m]
m = animal mass
b = slope of log-log plot
a = y-intercept of log-log plot
Levels of metabolism
standard metabolic rate (SMR) or basal metabolic rate (BMR) – energy required to
maintain basic biological functions independent of activity, digestion or the costs of
physical stressors
Routine metabolic rate (RMR) or field metabolic rate (FMR) – energy required for
‘normal activity’
Active metabolic rate (AMR) – energy required to perform specific levels of activity –
the energy required to fuel the maximum level of activity defined as maximum
metabolic rate (MMR)
Metabolic scope – the difference between SMR and MMR – has important
physiological/ecological implications as this is the energy available for an animal to
grow, digest food, support locomotion etc.
Temperature increase
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