Thermoregulation

What is a poikilotherm?

body temperature variable: T_{b (body)} ~=T_{a (ambient)}

What is a homeotherm?

body temperature relatively stable: T_b ~ constant

What is an endotherm?

body temperature derived from metabolism

What is thermoregulation?

actively regulating and/or maintaining body temperature

What are the primary challenges associated with being a warm-blooded endotherm living in the
marine environment?

• marine environment generally much colder than core body temperature

• water conducts heat 25x faster than air

• pinnipeds and phocids must thermoregulate in air and water

  fully aquatic mammals cannot dump heat if it gets too hot

What is convection?

heat loss to a fluid (movement of air or water)

What is conduction?

heat transfer to a solid

What is radiation?

transfer of radiant energy

What is evaporation?

heat loss absorbed from phase change liquid to water vapor (respiratory water loss)

What are the key variables of the heat loss equation?

kA(∆T)/L = heat loss

• k = conductivity of insulation material (how good is material at letting heat through it)

• A = body surface area (how much surface area for heat to leave)

• ∆T = temperature difference between body and water (greater difference = greater tendency to leave)

• L = thickness of insulation (affects speed of heat leaving

What is similar and different about conductivity and insulation?

They are on a scale; Insulators do not let heat through, while conductors are great at letting heat through. Blubber is somewhere in the middle, but does not give up as much heat as metals (similar to air)

What are the morphological adaptations that marine mammals have come up with to minimize heat loss?

• increased body size (decrease surface area to volume ratio)

• increase insulation (lowers conductance)

What are the two ways to increase insulation?

• increase blubber llayer

• increase density or length of hair

How does fur insulation work?

it traps air among the hairs, which provides insulation sea otters must add air back to fur after dive and it must stay clean to insulate

What is blubber made of?

continuous sheet of adipose tissue that is reinforced by collagen and elastic fibers so it remains under tension

Which marine mammals rely exclusively on blubber?

sirenians, phocids and cetaceans

Which marine mammals rely on fur?

mustelids and polar bears

Which marine mammals use both fur and blubber?

Otariids

What are the advantages of blubber?

• can withstand getting dirty

• does not compresss with depth

• able to dump heat

  • energy store

What are disadvantages of blubber?

• live tissue at low temperatures (could die)

• difficult to grow or divide at low temps

  • must haul out to molt and heat

What are advantages of fur?

• lighter than blubber

• better insulation for given amount in air

• skin is maintained at or near body temperature

  • ability to repair skin, molt, etc.

  • can do a slow molt since skin is usually around body temp

What are disadvantages of fur as an insulator?

• requires an air layer

• needs to be kept clean to be an insulator

  • insulation declines with depth (air bubbles leave)

How have marine mammals come up with physiological adaptations to lower heat los?

• lowering ∆T by lowering body temperature while diving

  • lowers O₂ use (reduce metabolism)

  • prolongs dive time

• vascular/physiological controls

  • counter current heat exchange

  • thermal windows and anastomoses

How does counter current exchange work?

veins surround arteries, and as the warm blood moves in an opposite direction to the veinous blood, heat from the warm, oxygenated blood will radiate to the cooler veinous blood

• with cocurrent exchange, some heat is exchanged but would eventually reach an equilibrium

What are some countercurrent arrangements?

• 2-3 veins around central artery

• central artery and main small veins

  • large artery, many small arteries and vessels

In marine mammals, peripheral blood vessels have counter current exchange (like dolphin flippers) so

freezing cold blood doesn’t return to the core and shock the body

In gray whale tongues there are

countercurrent exchange

In dolphin spermatogenesis..

cool blood from fins and fluke is preferentially sent to testes to cool the core blood before it reaches them, so that sperm is not fried

Where are thermal windows on marine mammals?

• flippers, fins, ears, and eyes (where no or poor insulation is)

  • in these areas CCHEs can be bypassed if they sendmore arterial blood here since not associated with veins if they want to dump heat

What are anastomoses?

• blood flow shunts (valves) that regulate the amount of blood movign through the blubber and reaching skin.

• hotspots will appear on the body where they begin dumping heat

• will open if long haul out, not necessarily if short haul out

In water, skin temperature is held near ambient water temperature, and a seal leaves

arteriovenous anastomoses closed

In air, skin is allowed to warm up, so a seal

opens arteriovenous anastomoses

What is the difference in the temperature differential of skin between water and air?

• water = small differential and animal can easily stay warm

• on land, large differential and cooling off.

How do marine mammals acclimatize to seasonal changes?

seasonal changes to thickness of the blubber

and composition of blubber

• colder water = thicker blubber

• warmer waters = thinner blubber

Saturated fats ____ the insulating capacity of blubber

increase.

What does unsaturated fats do for insulation of blubber?

Decreases because you can pack less in. (3 FAs verusus 6)

How does increasing metabolism help with heat loss?

increase heat production

Is metabolic rate higher in all species?

Metabolic rate is higher in some species including odontocetes, phocidae, otariidae, Enhydra lutris; Sirenains lower than predicted

What is the thermal nuetral zone?

range of environmental temperatures an animal can maintain T_b within and not need to increase metabolism

What is the effect of a higher metabolic rate on the TNZ?

It widens the zone, so the upper and lower critical temperatures increase.

Why are sea otters a bit of an outlier when it comes to their TNZ?

They spend their entire lvies outside of their TNZ; which is probably why they have one of the highest metabolic rates of any marine mammal

What is the heat increment of feeding (HIF)?

how sea otters maintain core body temp; goes up after feeding and goes down a lot during resting

What thermoregulatory challenges do pinniped pups have in air ?

• lanugo (dense coat of fine hair) insulates well on land but not waterproof

• they have high SA to volume ratio - lose heat quicker than adults

In air and water pinniped pups can

• specialized brown adipose tissue

• non-shivering thermogenesis (no ATP used to gen heat)

• large body size and or blubber reserves (load blubber on quick)

• produce heat via shivering

What are behaviorial adaptations to thermoregulate?

clump together to save heat

• decrease SA/ratio

haul out when warm in polar regions

line in water when warm (to cool)

sand flipping (cool sand on body as conduction

rest with thermal windows out of water

periodic migration to warm water