Topic 3

• Regulators

  Organisms that maintain a relatively constant internal environment despite changes in the external environment
• Conformers


  Organisms that allow their internal environment to vary with changes in the external environment
• Metabolic rate


  Rate of energy consumption
• Thermoregulation


  Controlling body temperature

  
• Thermal strategies


  • Endotherms
  • Ectotherms
• Endotherms


  Organisms that produce their own heat through metabolic processes
• Ectotherms


  Organisms that rely on external sources of heat to regulate their body temperature
• Mammals & birds have high metabolic heat production, all other animals have low metabolic heat production
• Smaller animals have higher rates of heat loss due to higher surface area to volume ratio
• Poikilotherms


  Organisms with variable body temperature
• Homeotherms


  Organisms with stable body temperature
• Heterotherms


  Organisms that exhibit patterns of variation in body temperature, either spatially or temporally
• The Devils Hole pupfish, Cyprinodon diabolis, lives in a hot spring with a constant water temperature of 33°C
• Metabolic heat production is negligible in ectotherms


  Ectotherms gain or lose heat from/to the environment
• Radiant heat


  Heat gained from energy in radiation (e.g. visible light – sun), but heat is also lost by radiation (lower energy – IR)
• Radiant heat


  • Behaviour (basking vs seeking shelter)
  • Colour (dark absorbs, light reflects)
  • Water absorbs radiant energy
• Conduction


  Direct transfer of energy via physical contact (gain or loss)
• Heat conduction is ~25x faster in water than air
• Convection


  Transfer of heat by movement of water or air (gain or loss)
• Evaporative heat loss


  Use of body water – gaping, tongue-lashing
• Evaporative heat loss remains the only way to lose heat when environmental temperature is higher than body temperature
• Endotherms have high metabolic heat production that dominates heat gain/loss
• Mechanisms to reduce and control heat loss in endotherms

  • Insulation (fur, feathers, fat)
  • Counter-current heat exchangers (reduce heat loss from appendages and respiratory system)
• Rete


  Counter-current heat exchanger that reduces heat loss from appendages
• Counter-current heat exchanger


  Reduces evaporative heat loss from the respiratory system
• Shivering thermogenesis


  Increasing metabolic heat production through muscle contractions
• Non-shivering thermogenesis


  Increasing metabolic heat production through brown adipose tissue
• Bergmann's rule states that terrestrial endotherms living at higher latitudes are larger and bulkier than related species at lower latitudes
• Oxygen is required for oxidative phosphorylation to produce ATP
• Oxyregulators


  Animals with limited ability to oxyconform (adjust to changes in oxygen availability)
• Rete


  A countercurrent heat exchanger
• Thermogenesis


  Boosting metabolic heat production
• Types of thermogenesis


  • Shivering thermogenesis
  • Non-shivering thermogenesis via brown adipose tissue (BAT) in mammals
• Brown adipose tissue (BAT)


  • Well-vascularized, mitochondrion-rich fat deposits
  • Contains thermogenin (uncoupling protein type I)
• Bergmann's rule postulates that terrestrial endotherms living at higher latitudes (i.e. further from the equator) are, on average, larger and bulkier than related species found at lower latitudes
• As latitude increases


  Terrestrial endotherms become larger and bulkier
• Oxyregulators


  Animals with limited ability to oxyconform
• Oxygen is required for oxidative phosphorylation
• Fuel + O2 -> ATP + CO2 + H2O
• Diffusion


  Movement of molecules from one region to another by Brownian motion, driven by partial pressure gradient