temperature 4: dealing with cold

Question 1

endotherms that deal with freezing temp; challenges and methods

Answer 1

(main concerns convection and radiation)

• pure water freezes at 0
• ice occupies 10% more space and requires energy to form
• tissues are 70-90% water
• plasma freezes at -1.6, seawater at -1.9
• air temp easily reaches -50+wind chill
  behaviours: migrating to warmers areas, burrow/huddling, or preparing in advance with food, insulation

Question 2

relaxed endothermy=temporary decrease of core Tb

Answer 2

• by temporarily lower BMR, heat production is reduced and enter a hypometabolic state
• this saves fuel when food is limited
  ie. topor overnight in birds and small mammals and hibernations over winter in mammals (mass affects entry for hibernation
• topor=U shaped, hibernations=L shaped with periodic arousals

Question 3

preventing freezing in ectotherms

Answer 3

1. stopping ice crystal growth

2. supercooling

Question 4

stopping ice crystal growth

Answer 4

• fish and insects can tolerate negative temp body fluids
• via antifreeze proteins (AFP) and glycoproteins (GP) stopping ice growth, bringing freezing point down to -2C
• AFP=multiple tandem sequences of Thr-Ala-Ala

Question 5

supercooling

Answer 5

• formation of ice requires NUCLEATING AGENT

- supercooling avoids nucleating agent at -10C, allows for many winter hardy insects

Question 6

controlled freezing in ectotherms through location and kinetics: intra vs extracellular ice formation

Answer 6

intracellular ice formation=draws water from extracellular space causes cells to swell and rupture and crystals puncture cell membrane
extracellular=more favorable because cells shrink and osmotically concentrate as water is drawn from them

Question 7

pre-freeze prep in frogs and insects

Answer 7

• make extracell nucleators, ie. long chain alcohols
• ice forms preferentially in extracell space at -7C
• make intracell solutes from large glycogen reserves that help retain cell water and stabilize tertiary structures

Question 8

regional endothermy in ectotherms:

Answer 8

1. preflight warming of thorax muscles in insects

2. elevated red muscles in tunas and some sharks

Question 9

pre-flight warming of thorax muscles in insects

Answer 9

• wing movement, antagonistic muscle contractions (shiver-like?), and futile cycling of glycogen (activation of glycolytic and gluconeogenic enzymes) warm thorax
• thorax warmed to 30C for take-off

Question 10

elevated red muscle in tuna and sharks

Answer 10

• aerobic red muscle is insulated by white muscle
• massive countercurrent arrangment of arterioles and venules keep heat from being lost in venous blood as it leaves red muscle; heat of arterial blood transfers to venous to keep red muscle warm throughout
• allows tuna to perform vertical foraging dives, cardiac temp kept=Ta

Question 11

behavioural thermoregulation: wanna-be endotherms

Answer 11

• (focused on conduction and radiation)
• reptiles regulate at 28-33C, metabolic heat not able to raise Tb>Ta
  1. must gain heat from environment via basking in radiant heat (direct/reflected solar heat, warmed surfaces), or conductive head (CONTACT with warm surfaces)
  2. control of blood flow to skin (form of internal convection)
• improves efficiency of heat gain/loss, acts as a regulatory system (similar appearance to topor)

Question 12

summary

Answer 12

• endothermy does not always mean constant or even Tb
• ectothermy does not always mean Tb=Ta
• animal life exists well below freezing, but not near boiling point