1. BIOLOGY 457/657 PHYSIOLOGY OF MARINE & ESTUARINE ANIMALS February 16, 2004 Water Balance in Aquatic Animals Osmoregulation in Invertebrates

2. BIOLOGICAL PROPERTIES OF WATER Is usually a liquid at the temperatures on Earth’s surface. Has a high specific heat. Has a high latent heat of vaporization Is denser in the liquid state than the solid state. Is a powerful solvent. Is a polar compound.

3. COLLIGATIVE PROPERTIES OF AQUEOUS SOLUTIONS Reduction in vapor pressure:  = original v.p. x (n solvent )/(n solvent + n solute ) Elevation in boiling point:  = +0.52°C per mole solute per liter H 2 O Reduction in freezing point:  = -1.86°C per mole solute per liter H 2 O Production of osmotic pressure:  V = nRT  = n/V x RT  (in atm) = 22.4 x C (moles/liter H 2 O)

4. TERMINOLOGY Mole = gram molecular weight Molar = moles per liter of solution Molal = moles per liter (1000g) of solvent (Note that this ratio determines colligative properties.) Osmole = grams of solute (per kg H 2 O) required to produce  = 22.4 atm Osmolal = number of osmoles per liter (kg) of H 2 O (For instance, in seawater 1000 mOsm/kg is equivalent to 1129 mM/kg. The osmotic concentration of a solution is its osmoticity)

5. OSMOSIS Definition: the movement of solvent through a semipermeable membrane due to its concentration gradient. (Note that no biological membrane is truly semipermeable.) Biological Significance of Osmosis: The actual pressure of osmosis applies to plants, not animals. Water movements that do occur quickly alter concentration gradients. In animals, it is often more useful to think of osmotic concentrations. It is important to distinguish between osmoticity and tonicity.

6. OSMOTIC COMPARTMENTS OF ANIMALS: Directions of Movement of Water & Solutes Internal Compartments Intracellular compartment Extracellular compartments Hemolymph (blood) Coelomic fluid

7. IONIC CONCENTRATIONS IN LIVING CELLS

8. ION REGULATION Even when tissues are isosmotic, ion compositions differ between tissues and water The details of ion regulation vary among taxa Within taxa, similar systems of regulation exist Ions frequently reduced in concentration: SO 4 =, Mg 2+ Ions frequently increased in concentration: K +, Ca 2+ Na + and Cl - tend to be similar to seawater concentrations

9. ION REGULATION (2) Solute concentrations in seawater, cells, and extracellular fluids.

10. ION REGULATION (3) Where are ions regulated? Cells - across the cell membrane Blood - across the gills, digestive tract, and extretory membranes Mechanism: ion transporters (ATPases)

11. ION REGULATION (4) Data: Adaptation in blue crabs (Callinectes sapidus) to changes in the osmolality of their tank (in the laboratory) Top: osmolality Bottom: ATPase activity

12. VOLUME REGULATION Whenever an animal moves into water of altered osmotic concentration, it will tend to gain or lose water. The process of controlling this expansion or shrinkage is called volume regulation.

13. VOLUME REGULATION (2) Water movement in the spider crab, Maja sp., upon transfer to 58% seawater (~580 mOsm) from 100% seawater. The crab rapidly gained weight at first, and also quickly lost salts to the more dilute medium to which it was transferred.

14. VOLUME REGULATION (3) How can a marine osmoconformer cope with this volume change? (1)Lowered salinity: Animal is hyperosmotic Animal tends to gain water and lose solutes * Reduce permeability * Produce a copious, dilute urine (2)Increased salinity: Animal is hyposmotic Animal tends to lose water and gain salts * Reduce permeability * Actively excrete salts

15. INTRACELLULAR ISOSMOTIC REGULATION Remember that animal cells must be in osmotic equilibrium with the extracellular fluids that surround them. Therefore, the cells must change in concert with these fluids. Cellular solutes: (1) Inorganic ions (2) α-amino acids (3) other small organic molecules; e.g. trimethyl amine oxide (TMAO), glucose, glycerol

16. INTRACELLULAR ISOSMOTIC REGULATION (2) Note the relatively serious effects on enzyme function of using inorganic salts or some charged amino acids. Neutral amino acids have almost no effect of PEP substrate binding.

17. INTRACELLULAR ISOSMOTIC REGULATION (3) Advantages of using amino acids as osmotic effectors: (1) No changes in electrical potential at neutral pH (2) Reduced direct effects on enzyme function

18. INTRACELLULAR ISOSMOTIC REGULATION (4)

19. INTRACELLULAR ISOSMOTIC REGULATION (5) Adjustment to hypotonic media: (1)Efflux of amino acids. (2)Incorporation of amino acids into proteins. (3)Deamination of amino acids and metabolic disposal of their products, with the production of NH 3. Adjustment to hypertonic media: (1)Protein hydrolysis to release free amino acids. (2)Uptake of amino acids in solution in blood. (3)Intracellular synthesis of new free amino acids.

20. INTRACELLULAR ISOSMOTIC REGULATION (6)

21. PATTERNS OF OSMOREGULATION (A)Freshwater hyperosmoregulators (B)Euryhaline hyper- and hypo- regulators, with reduced internal osmolality (C)Euryhaline hyperosmoregulators (D)Marine osmoconformers (E)Marine hyper- and hypo- regulators

22. OSMOCONFORMERS The relationship between medium concentration and blood concentration in several euryhaline invertebrates Callianassa californiensis Buccinum undatum Eupagurus bernhardus Porcellana platycheles P. longicornis Maia squinado Mercierella enigmatica

23. OSMOCONFORMERS (2) Found in echinoderms, cephalopods, sipunculids, ascidians, coelenterates, most marine molluscs, marine polychaetes, most marine crustaceans Only intracellular solutes (e.g. FAA) must be regulated May be associated with euryhalinity (e.g. molluscs) In intertidal habitats, animals often escape into tubes, burrows, or shells Can be associated with “apparent osmoregulation”, or osmotic buffering

24. OSMOCONFORMERS (3) Tidal buffering in the Chesapeake Bay oyster, Crassostrea virginica

25. HYPEROSMOTIC REGULATORS Limited hyperregulators (e.g. annelids, molluscs, some crustaceans) Reduced permeability to water and ions Intake of ions from food, active transport (gills?) Form a dilute urine Excellent hyperregulators (e.g. many crustaceans) Same mechanisms, but with more powerful physiological action

26. HYPER/HYPOSMOTIC REGULATORS Found in a few crustaceans; rare elsewhere Involves powerful, bidirectional ion transport systems NO invertebrate can produce a hypertonic urine for H 2 O conservation

27. LIFE IN TERRESTRIAL ENVIRONMENTS Life on land is analogous to life in hyperosmotic, aquatic environments. (1)Animals reduce water loss by reducing permeability, enclosing respiratory surfaces, and using ureotelic or uricotelic excretion (2)Animals increase water gain by moving to seawater, to damp locations, or by special physiological adapatations (next page).

28. THE LAND CRABS Terrestrial and semiterrestrial crabs, with varying ability to tolerate dessicating environments. Top, Ocypode quadrata: Ghost crabs extract soil interstitial water within their burrows, and are thus able to tolerate the extreme heat and dry conditions of open beaches. Middle, Cardisoma sp. These land crabs use water within the burrow, which may be required because their diet is extremely low-quality. Bottom, Gecarcinus lateralis. These crabs occupy dry burrows which they use as a refuge except when aerial humidity is high. Thus, they feed only intermittently, on low-quality plant food, and are slow-growing.