Lecture 3: Thermal Physiology Flashcards
Ecotherms
- poikilotherms (thermoconformers)
- regulatory ectotherms: still dependent on environment but exhibits some degree of control over body temp, in behavioral (e.g. move to cooler/warmer location) or physiological adjustments (e.g. changes in MR or blood flow to body parts).
Regulating heat transfer in REGULATORY ECTOTHERMS: behavioural & physiological adjustments
^ body temp by: gain external heat (e.g. basking), retain (vasoconstriction, blood vessels narrow, reduce blood flow, ^ blood pressure)& generate internal heat
Reduce by: lose internal heat(vasodilation, widen, ^ blood flow, reduce blood pressure), avoid external heat
Larger organisms = ^ SA to vol ratio, so can conserve lots of heat within cavities.
How do ectotherms cope with variable external temps?
Physiological adjustments:
1. THERMAL ACCLIMATISATION
- Phospholipid membranes: if too cold = too viscous, too warm = too fluid, these impair membrane function.
- HOMEOVISCOUS ADAPTATION: saturases (enzyme that ^saturation) & desaturases (reduce saturation), alter the fluidity.
- in warm adapted animals:^ saturated fatty acid tails & stabilisation with cholesterol =^ rigidity.
- in cold adapted: ^ unsaturated fatty acid tails, more space in membrane, more fluid.
- these retain the functions in the animals.
Thermal acclimatisation example
Experimental evolution: homeoviscous adaptation
- fruit flies reared for 3 years (lots of generations), exposed to 3 diff temps, high constant temp, low constant temp, & temp constantly moving between the 2, in variable environment had a much higher capacity to acclimatise to diff temps, measured by looking at ratio of phosphatidylethanolamine (PE) (unsaturated) & phosphatidylcholine (PC, saturated).
Developmental plasticity (sensitive to environmental factors in early life):
- samples from 3 diff popualtions, reared at 2 temps (16&25 ˚C), measured ratio of PE & PC in membranes, 16˚C had higher unsaturation (^fluid).
Example of thermal acclimatisation
Seasonal enzyme activity:
- poikilotherms in winter = MR reduced, still has to perform physiological functions, so compensatory ^ in metabolic enzyme activity.
- lactate dehydrogenase (LD) is key enzyme in glycolysis (converts lactate to pyruvate)
- winter acclimatised alligator & summer acclimatised in 3 diff temps, activity of winter acclimatised is ^.
Thermal adaptation
Proteins:
- too cold = non-flexible, too hot = lacks stability, these impairs function.
HOMEOFLEXIBILITY ADAPTATION: differences between species (inter-specific) rather than intra-specific. (Diff species have diff properties of enzymes so better adapted to diff temps).
- shape of LD changes when catalysing a reaction (open to closed shape, so flexibility important)
- cold adapted animals: ^ flexibility
- warm adapted: reduced flexibility but ^ thermo-stability (more stable at higher temps)
- at 0˚C activity of LD from Antarctic fish is higher than tropical animals
- HOMEOFLEXIBILITY ADAPTATION
- Cold-adapted animals often exhibit increased flexibility of proteins as an adaptive response to the challenges posed by low temperatures.
- important for maintaining cellular functions and ensuring the survival of these organisms in cold environments.
Here are several reasons why cold-adapted animals may have proteins with increased flexibility:
1. Maintaining Enzyme Activity: Low temperatures can decrease the kinetic energy of molecules, leading to reduced enzymatic activity. Proteins in cold-adapted organisms may have increased flexibility to counteract this effect, ensuring that enzymes remain active and efficient in catalyzing biochemical reactions at lower temperatures.
2. Optimizing Membrane Fluidity: Proteins play a role in regulating membrane fluidity. Cold-adapted organisms may have proteins with increased flexibility to help maintain an optimal level of membrane fluidity at lower temperatures. This is crucial for maintaining the function of membrane-associated proteins and overall cellular integrity.
Thermal protection
HEAT SHOCK PROTEINS
- in all animals
- Hsp90, Hsp70, Hsp40
- are molecular chaperones (form a complex all together & bind to damaged proteins, takes 2ATP, protein gets refolded)
- highly inducible by temp & other stressors
Cold protection
- FREEZE TOLERANCE - the wood frog in Alaska can tolerate being frozen (immobile) for ~200 days. Produce ^ quantity’s of cryo-protectants e.g. glucose & urea in cells & prevents osmotic movement of liquids, if cells freezing ice reduces concentration of H2O, H2O moving between cells, glucose & urea prevent that movement.
Cold protection
- Freeze-avoidance
- polar fish & invertebrates e.g. Atlantic cod produce anti-freeze glycoproteins
- prevent uncontrollable ice crystal growth in extra cellular fluid
Endotherms
Advantages:
+ high, constant MR
+ are optimal temp for cellular activities = competitive advantage
Disadvantages:
- high energetic cost
Evolution of endothermy
Paper by Legendre & Davesne (2020)
- all birds, mammals are endotherms
- independently evolved endothermy with diff mechanisms of heat generation
Stable core temp
- endotherms have stable core temp
- birds have ^ MR (use more energy for flying) easier to warm up than cool down so generally have higher body temp
Gain external heat
Behavioural adjustment:
- basking (e.g. cats)
- migration/movement (e.g. humpback whale, in winter moves to warmer temps to breed, better for production of offspring)
Physiological adjustment:
- increase absorbance (animals darker in colour
Retain internal heat
- vasoconstriction
- insulation (anatomical (e.g. ^ supplies of fat, fur) & behavioural (animals huddle or build burrows)
- counter-current exchange (counter current flow of Venus & arterial blood) (e.g. bird leg is long & skinny & large SA for heat loss, wants to get blood down to foot but doesnt want to loose lots of heat, so have counter-current exchange mechanism, known as rete mirabile, dense network of Venus & arterial blood capillaries, arterial blood flowing down from heart & Venus blood returning up the leg, close together so allows heat to be transferred from arterial blood to Venus blood.
