Fundamentals of Water Relations and Thermoregulation in Animals

Abstract

Animals must maintain their internal environment relatively constant with respect to water, electrolytes and temperature. The process by which they regulate the concentration of their internal water and solute concentrations is called osmoregulation. Osmoregulation is accomplished by physiological, anatomical and behavioural adaptations. These include adaptations that modify the permeability of external surfaces and the development of specialised structures that actively transport solutes and metabolites. Animals face the greatest osmoregulatory challenge in terrestrial environments because concentration gradients there are the greatest. As evaporative cooling is used for thermoregulation in terrestrial environments, animals are often faced with the dilemma of maintaining either water or thermal balance, but not both.

Key Concepts:

  • Water and solute balance is maintained by ensuring that the rate of water and solute loss is equivalent to the rate of water and solute coming into the animal.

  • Water and electrolytes can enter or leave the body by exchange across the skin and respiratory surfaces and can be gained through ingestion of food and lost through excretion (faeces or urine).

  • Metabolic processes produce both water and nitrogenous waste products. Nitrogenous wastes are excreted through specialised structures.

  • Desert animals have special adaptations to reduce water loss, which include allowing body temperatures to drift, avoidance of warm temperatures by burrowing or nocturnal behaviour.

  • Aquatic animals primarily excrete their nitrogenous wastes as ammonia, whereas terrestrial animals where water is less available excrete either urea (mammals and amphibians) or uric acid (birds and lizards).

  • Elasmobranchs (sharks and rays) retain urea in their body fluids to maintain a beneficial osmotic gradient. The toxic effects of elevated concentrations of urea are alleviated by the presence of TMAO.

  • Terrestrial animals reduce permeability of their skin by adding layers of lipid, keratin or chitin. Arthropods have the lowest rate of cutaneous water loss.

  • Marine lizards and birds have evolved specialised glands that allow for the excretion of excess salt, whereas mammals have evolved kidneys that can excrete highly concentrated urine.

  • Some animals employ behaviour to find microclimates that allows them to exist within extreme environments, thus allowing them to exist there in the absence of physiological or anatomical adaptations.

Keywords: osmoregulation; metabolism; electrolytes; nitrogenous wastes; evaporative water loss; urea; uric acid; kidney; salt gland

Figure 1.

A simple schematic of the primary processes important to maintain cellular homeostasis.

Figure 2.

The avenues of water intake and loss and electrolyte intake and loss are shown for freshwater and marine teleost fish.

Figure 3.

Schematic of where water and electrolytes enter and leave the body for a marine mammal and in this case excretion of electrolyte and water as milk only occurs when females are lactating.

Figure 4.

Skull of a California sea lion with an exploded view showing the nasal turbinates. Photo by J. Hiatt.

Figure 5.

Nitrogen as a waste product is excreted in three different chemical forms depending on the organism.

Figure 6.

The overall shape of mammalian kidneys varies with marine mammals showing the greatest development of a reniculate or lobulate kidney. Adapted from Slijper .

Figure 7.

Diagram of a mammalian kidney. A single nephron is shown. Blood passes through a capillary network called the glomerulus and an ultrafiltrate passes into the Malpighian body, active transport occurs in the tubules and within the loop of Henle; a concentration gradient is created that allows resorption of water as the filtrate passes through the collecting duct. Reprinted with permission from Schmidt‐Nielsen . Copyright 1990 Cambridge University Press.

Figure 8.

Cape ground squirrels are active during the day, periodically retreating to their burrows to cool down. Their tail is used as a parasol helping to shade the body from the sun. Note the position of the shadow, indicating that the animal is facing with its back towards the sun. Photo by Dan Costa.

Figure 9.

Large mammals like this African black‐backed jackal find shade under trees and shrubs during the hottest part of the day. This saves water by reducing the need to use evaporative cooling. Photo by Dan Costa.

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References

Amey AP and Grigg GC (1995) Lipid‐reduced evaporative water loss in two arboreal hylid frogs. Comparative Biochemistry and Physiology Part A: Physiology 111: 283–291.

Bennett AF, Huey RB, John‐Alder H and Nagy KA (1984) The parasol tail and thermo regulatory behavior of the cape ground squirrel Xerus inauris. Physiological Zoology 57: 57–62.

Beuchat CA (1996) Structure and concentrating ability of the mammalian kidney: Correlations with habitat. American Journal of Physiology 271: R157–R179.

Bradley TJ (2006) Discontinuous ventilation in insects: protecting tissues from O2. Respiratory Physiology & Neurobiology 154: 30–36.

Bradley TJ (2007) Control of the respiratory pattern in insects. In: Roach RC, Wagner PD and Hackett PH (eds) Hypoxia and the Circulation, p. 211–220. New York: Springer.

Braun EJ (1999) Integration of organ systems in avian osmoregulation. Journal of Experimental Zoology 283: 702–707.

Clement ME, Munoz‐Garcia A and Williams JB (2012) Cutaneous water loss and covalently bound lipids of the stratum corneum in nestling house sparrows (Passer domesticus L.) from desert and mesic habitats. Journal of Experimental Biology 215: 1170–1177.

Costa DP (2009) Osmoregulation. In: Perrin WF, Thewissen JGM and Wursig B (eds) Encyclopedia of Marine Mammals, p. 801–806. San Diego: Academic Press.

Evans DH (2010) A brief history of fish osmoregulation: the central role of the Mt. Desert Island Biological Laboratory. Frontiers in Physiology 1: 1–10.

Franz R, Hummel J, Muller DWH et al. (2011) Herbivorous reptiles and body mass: effects on food intake, digesta retention, digestibility and gut capacity, and a comparison with mammals. Comparative Biochemistry and Physiology – Part A: Molecular & Integrative Physiology 158: 94–101.

Gibbs AG (1998) Water‐proofing properties of cuticular lipids. American Zoologist 38: 471–482.

Hammerschlag N (2006) Osmoregulation in elasmobranchs: a review for fish biologists, behaviourists and ecologists. Marine and Freshwater Behaviour and Physiology 39: 209–228.

Hertel LA (1993) Excretion and osmoregulation in the flatworms. Transactions of the American Microscopical Society 112: 10–17.

Hetem RS, Strauss WM, Fick LG et al. (2012) Does size matter? Comparison of body temperature and activity of free‐living Arabian oryx (Oryx leucoryx) and the smaller Arabian sand gazelle (Gazella subgutturosa marica) in the Saudi desert. Journal of Comparative Physiology B: Biochemical Systemic and Environmental Physiology 182: 437–449.

Hildebrandt JP (2001) Coping with excess salt: adaptive functions of extrarenal osmoregulatory organs in vertebrates. Zoology (Jena, Germany) 104: 209–220.

Hillenius WJ (1992) The evolution of nasal turbinates and mammalian endothermy. Paleobiology 18: 17–29.

Hillyard SD (1999) Behavioral, molecular and integrative mechanisms of amphibian osmoregulation. Journal of Experimental Zoology 283: 662–674.

Hofmeyr MD and Louw GN (1987) Thermoregulation pelage conductance and renal function in the desert‐adapted springbok Antidorcas marsupialis. Journal of Arid Environments 13: 137–152.

Hui CA (1981) Sea water consumption and water flux in the common dolphin Delphinus delphis. Physiological Zoology 54: 430–440.

Huntley A, Costa D and Rubin R (1984) The contribution of nasal countercurrent heat exchange to water balance in the northern elephant seal, Mirounga angustirostris. Journal of Experimental Biology 113: 447–454.

Johnson WE, Hillyard SD and Propper CR (2010) Plasma and brain angiotensin concentrations associated with water response behavior in the desert anuran, Scaphiopus couchii under natural conditions in the field. Comparative Biochemistry and Physiology – Part A: Molecular & Integrative Physiology 157: 377–381.

Jorgensen CB (1997) 200 years of amphibian water economy: From Robert Townson to the present. Biological Reviews of the Cambridge Philosophical Society 72: 153–237.

Karel S (1999) Active regulation of insect respiration. Annals of the Entomological Society of America 92: 916–929.

Lester CW and Costa DP (2006) Water conservation in fasting northern elephant seals (Mirounga angustirostris). Journal of Experimental Biology 209: 4283–4294.

Lockey KH (1988) Lipids of the insect cuticle: origin, composition and function. Comparative Biochemistry and Physiology – Part B: Biochemistry & Molecular Biology 89: 595–645.

Louw GN (1993) Physiological Animal Ecology, 1st edn. New York: John Wiley & Sons.

Maddrell S (2009) Insect homeostasis: past and future. Journal of Experimental Biology 212: 446–451.

McClanahan L (1967) Adaptations of the spadefoot toad Scaphiopus couchi, to desert environments. Comparative Biochemistry and Physiology 20: 73–99.

McWhorter TJ, Caviedes‐Vidal E and Karasov WH (2009) The integration of digestion and osmoregulation in the avian gut. Biological Reviews 84: 533–565.

Nordlie FG (2009) Environmental influences on regulation of blood plasma/serum components in teleost fishes: a review. Reviews in Fish Biology and Fisheries 19: 481–564.

O'Donnell MJ (2009) Too much of a good thing: how insects cope with excess ions or toxins in the diet. Journal of Experimental Biology 212: 363–372.

Sabat P, Maldonado K, Fariña J and del Rio C (2006) Osmoregulatory capacity and the ability to use marine food sources in two coastal songbirds (Cinclodes: Furnariidae) along a latitudinal gradient. Oecologia 148: 250–257.

Schmidt‐Nielsen K (1990) Animal Physiology: Adaptation and Environment, 4th edn, p 366. Cambridge, UK: Cambridge University Press.

Schwimmer H and Haim A (2009) Physiological adaptations of small mammals to desert ecosystems. Integrative Zoology 4: 357–366.

Shoemaker V and Nagy KA (1977) Osmoregulation in amphibians and reptiles. Annual Review of Physiology 39: 449–471.

Slijper EJ (1962) Whales. Ithaca, NY. Cornell University Press.

Van Valkenburgh B, Curtis A, Samuels JX et al. (2011) Aquatic adaptations in the nose of carnivorans: evidence from the turbinates. Journal of Anatomy 218: 298–310.

Whittow GC (1987) Thermoregulatory adaptations in marine mammals: interacting effects of exercise and body mass. A review. Marine Mammal Science 3: 220–241.

Williams JB (1996) A phylogenetic perspective of evaporative water loss in birds. Auk 113: 457–472.

Williams JB, Lenain D, Ostrowski S, Tieleman BI and Seddon PJ (2002) Energy expenditure and water flux of Ruppell's foxes in Saudi Arabia. Physiological and Biochemical Zoology 75: 479–488.

Williams JB, Siegfreid WR, Milton SJ et al. (1993) Field metabolism, water requirements, and foraging behavior of wild ostriches in the Namib. Ecology 74: 390–404.

Yancey PH (2005) Organic osmolytes as compatible, metabolic and counteracting cytoprotectants in high osmolarity and other stresses. Journal of Experimental Biology 208: 2819–2830.

Further Reading

Baldisserotto B, Mancera Romero JM and Kapoor BG (2007). Fish Osmoregulation. Boca Raton, FL: Science Publishers.

Bentley PJ (2002) Endocrines and Osmoregulation: A Comparative Account in Vertebrates. Berlin: Springer‐Verlag.

Bradley TJ (2009) Animal Osmoregulation. Oxford, UK: Oxford University Press.

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Costa, Daniel P, Houser, Dorian S, and Crocker, Daniel E(Nov 2013) Fundamentals of Water Relations and Thermoregulation in Animals. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0003216.pub2]