Polar seas: Adaptation to the cold

Question 1

What care the effects of the ozone hole, and excess UVB?

Answer 1

•Absorption of UV can also disrupt RNA, proteins (enzymes & hormones) and pigments

Question 2

what are some physiological adaptations to avoiding UV damage?

Answer 2

• Protection provided by absorbent substances – melanin
• Mycosporine amino acids – invertebrates and algae (Karentz et al., 1990)

Question 3

what are some behavioural adaptations to avoiding UV damage?

Answer 3

• Organism behaviour is often adapted to avoid direct sunlight and harmful UV-B
• Marine mammals are most at risk when ashore, darker skin pigments – melanin provides protection.
• Fur and feathers – eggs protected by adults
• Penguins have adapted corneas – higher UV threshold compared to domestic fowl – snow blindness? (Hemmingson & Douglas, 1970)
• Southern Elephant Seal (Mirounga leonina) – solute concentration in tears show strong absorption for wavelengths <300nm

Question 4

What is the effect of low temperatures on cell physiology?

Answer 4

• Reduction in the proportion of molecules in a sufficiently activated state
• As long as water is available then biochemical processes can continue at lower rates at temperatures <0oC
• Cold can affect the lipid bi-layers of cell membranes – liquid crystal to gel transition

Question 5

Psychrophiles

Answer 5

•Psychrophiles have higher proportion of unsaturated and short-chain fatty acids (52%)

Question 6

Effects of freezing

Answer 6

• The effects of freezing are distinct from those of low temperature
• Chill does not necessarily involve the separation of ice or changes in water soluble components of cells and tissues
• Freezing requires the presence of nuclei for ice crystal formation
• Nucleation is catalysed by particulate matter in a specific molecular configuration (nucleators) – unfortunately for invertebrates nucleators are present in food material!
• When ice forms solutes are excluded from the crystals, raising the concentration in the remaining liquid
• Osmotic stress is the immediate and most injurious consequence (biggest problem)
• Reduction in cell volume may lead to injury – impairing membrane resilience may lead to cell bursting on thawing

Question 7

Freezing and freeze resistance

Answer 7

• Production of compatible solute substances to counter freezing effects
• May be free amino acids or sugars
• Must be soluble and metabolically inactive
• Glycerol etc may act as cryoprotectants – water replacement agents
• These substances can correct osmotic imbalance brought about by freezing – colligative (proportional to solute concentration)
• Changes in membrane elasticity can make cells more able to withstand contraction and expansion stresses
• Freeze resistance may take minutes to several days/weeks to develop

Question 8

Avoidance of freezing and chill

Answer 8

• Avoiding or inhibiting nucleation at sub-zero temperatures prevents freezing
• Marine fish have blood freezing points between -0.9 and -1.0oC
• Absence of ice nuclei allows them to live in deep water (-1.8oC) where they remain in a supercooled state
• Antifreeze compounds occur universally in Antarctic fish but less common in Arctic fish
• Mammals and birds utilise heat released from metabolic processes
• Marine mammals utilise insulation (blubber) and have low surface area/volume ratios to reduce heat loss as the water can support a bulkier body

Question 9

described antarctic fishes

Answer 9

Dominated by the sub-order Notothenioidei

6 families, 39 genera and 91 species

Including the Antarctic cods and the Ice fishes

Lack swim bladders - majority are demersal

Large commercial fisheries with >500,000 tonnes of Notothenia rossi landed from South Georgia fishery

Question 10

What are the specialist adaptations of the notothenioid?

Answer 10

• •Presence of macromolecular antifreeze substances in body fluids, which are required to maintain an internal concentration (Marine teleosts 1/3 ) and to stop the blood freezing (Blood freezes at -0.8oC – Antarctic seas may reach -1.9oC).
• •Cryoprotectants act to reduce the freezing point of the blood in these fishes
• •The fishes produce glycopeptides, which is a non-colligative mechanism (not proportional to the amount – about 4% is peak effectiveness).
• •They inhibit the growth of ice crystals by
• competitively adsorbing to the surface of
• water molecules as they start to form this
• crystalline structure and they block the
• formation of these ice nuclei.

Question 11

What are glycopeptides?

Answer 11

• Have been found in the blood plasma of all Antarctic notothenioids (with the exception of Lepidonotothen kempi)
• Function differently to antifreeze additives, such as salt or ethylene glycopeptides at the ice-solution interface adsorbing to minute ice crystals
• Inhibit growth by producing a barrier between ice and water molecules
• May coat crystals as they are swallowed when fish drinks (Peterson, 1986)

Question 12

How does the presence of ice effect when fish freeze?

Answer 12

• Subsequent exposure to ice-laden seawater at -1.9oC reintroduces ice nuclei and the fish freeze above -2.2oC
• AFGPs must act as a barrier to ice propagation across the integument and in tissue fluids (De Vries, 1988)

Question 13

What is the main source of glycoprotein synthesis?

Answer 13

The liver

Question 14

Antifreeze is secreted into the blood and appears in most fluids except for

Answer 14

•urine, occular fluid and cellular cytoplasm

Question 15

•These fluids protected from ice crystal invasion as surrounding tissues are fortified with antifreeze (De Vries, 1988)

AFGP synthesis occurs for how much of the year in Antarctic and Arctic fish?

Answer 15

•AFGP synthesis is year round in Antarctic fish whereas it only occurs in Arctic fish during winter

Question 16

Oxygen transport and blood physiology

• With the exception of 1 family, heart size and blood volume in Notothenioids is similar to temperate fishes, even without haemoglobin and the higher viscosity of blood due to cold temperatures.
• Gill surface area is relatively low but there is a huge increase in the amount of cutaneous gas exchange.

How is this achieved?

Answer 16

• Highly vascularised
• Low O2 affinity
• cutaneous O2 uptake
• Reduced need for haemoglobin
• Haematocrit (or packed cell volume)

Question 17

Notothenoids - surviving without haemoglobin

Highly vascularised

Answer 17

•Notothenoids, especially ice fish are very fleshy, don’t have obvious scales and are highly vascularised so they can absorb oxygen straight from the water across the epithelium of the skin into the blood vessels. They can do this because colder seawater contains a higher partial pressure of oxygen – steep diffusion gradient.

Question 18

Notothenoids - surviving without haemoglobin

Low O2 affinity

Answer 18

•Most species also have a low O2 affinity (Kunzmann & di Prisco, 1991) – probably due to being available in high quantities, (not beneficial to oxygen uptake).

Question 19

Notothenoids - surviving without haemoglobin

cutaneous O2 uptake

Answer 19

• Unresolved whether cutaneous O2 uptake can compensate for reduced gill uptake
• As fish get bigger relative surface area decreases and diffusion distance and time increase – possible more effective for juvenile or fish with low metabolic rate.

Question 20

Notothenoids - surviving without haemoglobin

Reduced need for haemoglobin

Answer 20

In polar fish high ambient PO2, high solubility in blood plasma, lower metabolic rates and higher blood viscosity and therefore a reduced need for haemoglobin.

Polar fishes show reductions in a) erythrocyte number, and b) amount of haemoglobin and myoglobin

Question 21

Notothenoids - surviving without haemoglobin

Haematocrit (or packed cell volume)

Answer 21

• Haematocrit (or packed cell volume) – “proportion of blood volume occupied by red blood cells”
• It is a major determinant of blood viscosity
• Viscosity increases at low temperatures and low flow rates

Question 22

Give an example of the physiology of a notothenioid.

Answer 22

Pagothenia borchgrevinki

• Grows up to 28cm
• Spends its time under the ice at depths up to 550m
• Blood is 70% more viscous at -1.8oC than at 15oC
• Reduction, or loss, of erythrocytes, partly offsets the effects of low temperature and low flow rates on blood viscosity (MacDonald et al., 1987)

Question 23

What are the adaptations of the ice fish?

Answer 23

O2 carrying capacity is only 10% of red-blooded Notothenioids

• Low temperature lowers metabolic requirement for O2 whilst increasing amount that can be dissolved in seawater and body fluids
• Total O2 capacity increased by large blood volume, 8-9% of body mass - 2-4 x comparable nototheniids
• Blood passages in secondary gill lamellae are larger than in other teleosts
• Cutaneous respiration in highly vascularised tail section may aid gas exchange
• They actively keep water flowing over the gills.
• •Ventricle and thickness of cardiac muscle in ice-fish are 2-3x larger
• •Stroke volume is 6-15x time greater
• Better designed for developing pressure with low muscle tension – less exertion on myocardial wall
• Low myoglobin may locally enhance O2 diffusion
• Density of mitochondria on myocytes is higher than any other vertebrate
• Cardiac and respiratory work account for 50% of resting metabolism

Question 24

Ice fish - what are the disadvantages of a lack of haemoglobin?

Answer 24

• Reduced ability to withstand hypoxia i.e <40-50 mmHg – loose flexibility to adapt (Hemmingsen & Douglas, 1972)
• Resting ice-fish use 60-70% of O2 carrying capacity for resting metabolism
• Red-blooded notothneiids use only 20-30% even though consumption rates are similar

Question 25

Ice fish - what are the advantages of a lack of haemoglobin?

Answer 25

So do Antarctic fish need haemoglobin at all?

• Blood does not have same transport requirements as temperate fish
• Sluggish fish can lose haemoglobin with no disastrous effects (Kunzmann 1991)
• Satisfy O2 demands from O2 dissolved in the plasma

Question 26

Penguins: cold adaptations

Answer 26

• Flippers and feet have a vascular counter-current heat exchange system
• Metabolic rate can be maintained at a normal level down to -10oC, can also be lowered by lowering breathing rate
• Huddles – often up to 5000 male birds, 10m-2
• Moves downwind as birds on the windward side move along the flanks and re-enter on the lee side
• The temperature inside the huddle can reach +24oC
• This behavior can cut daily loss of body weight by 25-30%
• Male s lose ≤40% of summer body weight by the end of the winter

Question 27

Penguins: diving adaptations

Answer 27

• Emperor’s have specialised haemoglobin molecules that allow them to bind O2 at low PO2
• Adapted myoglobin in the muscles allows for efficient transport of O2
• Avoid barotaruma from deep dives by having solid bones rather than air filled
• Variable heart rate to cope with low O2 during dive
• Resting 60-70bpm, pre-dive 180-200bpm, dropping to 20bpm during dive