BIOLOGY 457/657 PHYSIOLOGY OF MARINE & ESTUARINE ANIMALS

1. BIOLOGY 457/657PHYSIOLOGY OF MARINE & ESTUARINE ANIMALS February 4, 2004 Physiological & Biochemical Adaptation

2. MECHANISMS OF ADAPTATION Adaptation: Adjustment or design of an organism to function effectively in its normal environment. Acclimation: Long-term changes in physiological conditions to maintain routine function when new, stable external environments are encountered. Acclimatization: Physiological adjustment to function optimally in the face of many fluctuating seasonal variables.(Not commonly used, and generally refers to plants).

3. ADAPTATION Adaptation can be genetic, developmental, or environmentally induced. Adaptation can be evolutionary or physiological. CAPACITY vs. RESISTANCE adaptations: Capacity adaptations are the routine adjustments made to changing condition that provide long-term homeostasis in the face of continuous environmental change. Capacity adaptations are a normal aspect of life. Resistance adaptations are those that come into play at the very limits of an organism’s ability to survive. Resistance adaptations are necessarily transient, emergency measures.

4. CONFORMITY vs. REGULATION A conformer maintains an internal condition that varies in the same way as environmental conditions. Changes in internal states are tolerated. A regulator maintains a constant (or nearly constant) internal environment in the face of varying external conditions.

5. LETHAL LIMITS Resistance adaptations occur at environmental extremes, limiting animal distributions in time and space. The LD50(dose for 50% survival in a population in a specified time) is commonly used to define resistance to a particular stressor. Alternatively, the survival time (or time to some other measure) of animals can be used to measure their stress tolerances.

6. LETHAL LIMITS EXAMPLE As one would expect, the factors that limit survival interact, so the zone of resistance for a particular environmental stressor depends of the nature of other, simultaneous stresses. Also, the ability to tolerate stress changes with acclimation.

7. EFFECTS OF ACCLIMATION ON RESISTANCE

8. MOLECULAR MECHANISMS OF ADAPTATION • Alterations in metabolic pathways. For instance, a change from carbohydrate to fat metabolism or a shift to the hexose monophosphate shunt at low temperatures. • Alterations in enzyme concentration. Many enzymes associated with the Krebs cycle or the electron transport chain increase in concentration with decreasing temperature. • Differential synthesis of allozymes and/or isozymes. Changing expression of genes can lead to the synthesis of other enzymes more appropriate to current conditions.

9. AN EXAMPLE OF MOLECULAR ADAPTATION:Allozyme frequency in killifish (Fundulus heteroclitus) Respiratory enzymes (here: LDH-Bb, MDH-Ab, & GPI-Bb) vary clinally with latitude. The change is almost certainly a reflection of adaptation to temperature.

10. RESISTANCE TO HIGH TEMPERATURE:Myofibrillar ATPase of Fishes

11. RESISTANCE TO HIGH TEMPERATURE:Heat-Shock Proteins (HSPs) These proteins are quickly produced in conditions of elevated temperature, preventing aggregation of unfolded proteins and assisting their recovery to the active state.

12. RESISTANCE TO LOW TEMPERATURE:Antifreeze Proteins of Antarctic Fishes These unusual polypeptides actually interfere with the production of ice crystals in living tissues at very low temperatures.

13. RESISTANCE TO LOW TEMPERATURE:Antifreeze Proteins of Antarctic Fishes (2)

14. CAPACITY ADAPTATION TO TEMPERATURE At any given temperature, reactive molecules exist in a population of different energy states. Only the extremely active members of the population will enter a metabolic reaction. This is the origin of Q10effects. Animals living at different temperatures must cope with changing activation energies.

15. CAPACITY ADAPTATION TO TEMPERATURE ACTIVITY COMPENSATION Enzymes involved in energy metabolism in tropical and Antarctic fish differ greatly in their activity levels at identical temperatures. Note, however, that the activities in Antarctic fish are still about half those of the tropical fish at their normal environmental temperature ranges.

16. CAPACITY ADAPTATION TO TEMPERATURE AFFINITY COMPENSATION Enzymes from fishes living in different thermal habitats can be adapted to have similar or identical binding constants (Kms) in at very different temperatures. (This example is for A4-LDH.) This presumably reflects a parallel evolutionary adjustment for maintaining constant function in very different environments.

17. CAPACITY ADAPTATION TO TEMPERATURE“Homeoviscous” adaptations in cellular membranes The physical properties of living membranes depend on the makeup of the proteins and phospholipids incorporated in them. In particular, the fluidity of the membrane (its viscosity) is determined by the ability of membrane lipids to pack tightly. Since unsaturated fatty acids have “kinks” in their hydrocarbon tails, they are more difficult to pack and produce membranes that are inherently less viscous.

18. CAPACITY ADAPTATION TO TEMPERATURE“Homeoviscous” adaptations in cellular membranes At lower temperatures, cell membranes contain increasing concentrations of unsaturated fatty acids in their membrane phospholipids. This maintains membrane fluidity at low temperatures, where membranes otherwise would coalesce and “freeze”.

19. CAPACITY ADAPTATION TO TEMPERATUREHeterothermy in scombrids & some sharks Peripheral circulation in tunas is uniquely adapted to conserve deep-body temperature.

20. CAPACITY ADAPTATION TO TEMPERATUREThe rete in bluefin tuna

21. CAPACITY ADAPTATION TO TEMPERATUREField measurements of heterothermy in scombrids

22. CAPACITY ADAPTATION TO TEMPERATURE“Brain heaters” in fast-swimming predatory fishes BROWN-FAT HEATERS Some extremly high-speed predators (e.g. swordfish, marlin) use heat generated by mitochondrial respiration to warm their brains and retinas. (Carey, 1982)

23. CAPACITY ADAPTATION TO TEMPERATUREImages of the “brain heater”