C. Barker Jørgensen

On gill function in the mussel Mytilus Edulis L.

Abstract The function of the gill of the mussel Mytilus edulis (L.) has been studied in intact animals and in animals with cut posterior adductor muscle, as well as on gill fragments and isolated gill filaments. Intact 3–4 cm long specimens, kept singly in glass jars containing 600 ml aerated sea-water at 1–2° or 14°C, were able to clear suspensions of various particles at high rates. The gills retained almost completely particles down to about 3–5 µm in diameter (yeast cells or latex spheres, and about half of particles 1–2 µm in diameter (Bacterium sp. or latex spheres). The immediate effect of cutting the adductor muscle was to decrease the retentiveness of the morphologically intact gills; later also the rate of water transport decreased. In intact, fully open mussels, 10−7-10−5 M dopamine (DA) or 10−7-10−6 M serotonin (5-HT) did not affect the rates at which the mussels cleared suspensions of yeast, whereas 10−5 M 5-HT strongly reduced clearances of suspensions of yeast and 18 µm Tetraselmis cells, t...

200 YEARS OF AMPHIBIAN WATER ECONOMY: FROM ROBERT TOWNSON TO THE PRESENT

In the 1790s, Robert Townson established the main features of the water economy of terrestrial amphibians: rapid evaporative water loss in dry surroundings,‘drinking’ by absorption of water through the abdominal skin pressed against moist substrates, and use of the urinary bladder as a reservoir from which water is reabsorbed on land. This knowledge was of little interest to the establishment in the first half of the nineteenth century of experimental physiology as a basic medical discipline, when frogs became models in the elucidation of general physiological processes. Townsons pioneer contributions to amphibian physiology were forgotten for 200 years (Jørgensen 1994 b). Durig (1901) and particularly Overton (1904) restored knowledge about amphibian water economy to the level reached by Townson, but the papers had little impact on the young science of animal physiology because they primarily aimed at elucidating the transport of fluids across membranes. Frog skin remained a model preparation in such studies throughout the century. With the establishment of terrestrial ecology early in the century, the relations of animals, including amphibians, to water became a central theme. Concurrently with comparative studies of amphibian water economy in an ecological setting, the subject proceeded as an aspect of animal osmoregulation. Adolph (1920‐1930) and Rey (1937 a) established the highly dynamic nature of water balance in amphibians in water and on land. Their observations indicated functional links between environment, skin and kidneys, the nature of which remained to be explored. Thorson & Svihla (1943) reopened the ecological approach in a comparative study of the relations between amphibian habitat and tolerance of dehydration. By mid‐century, the central themes of amphibian adaptations to terrestrial modes of life were re‐established, except for the function of the bladder as a water‐depot. During the following decades, a rich literature appeared, particularly focusing on adaptations of amphibians to arid environments. Thus, in the 1970s, it was found that ‘waterproofing’ of the highly permeable skins by means of skin secretions had evolved independently in several families of tropical arboreal frogs, and that a number of amphibians that aestivate whilst burrowed in dry soil could reduce evaporation by forming cocoons from shed strata cornea. In 1950–1970 the role of bladder urine as a water depot in terrestrial amphibians was recognized: this did not change the established view of water balance in terrestrial amphibians as alternating between dehydration on land and rehydration in response to the deficit in body water. Amphibians may, however, maintain normal water balance whether the ambient medium is water or air by means of little understood integrated mechanisms in control of cutaneous drinking behaviour, water permeability of the skin and bladder wall, and urine production.

Growth efficiencies and factors controlling size in some mytilid bivalves. Especially Mytilus edulis L.: review and interpretation

Abstract Data from the literature on rates of growth and metabolism, mainly in Mytilus edulis, but also in M. californianus and Modiolus demissus have been used in an attempt to estimate the maximum rates at which mussels can convert absorbed food energy into growth and reproduction, and to evaluate which factors control these maximum net growth efficiencies. It is concluded that high maximum growth efficiencies can be maintained at a constant level up to a certain critical body size above which the maximum growth efficiency declines with increasing size. The critical body size at which growth efficiency starts to decline is independent of the initial level of maximum growth efficiency. The maximum body size that can be attained depends upon the body size at which the growth efficiency starts to decline and the rate at which it is declining. It is argued that the declining growth efficiency above a critical body size results from a decelerating mean rate of water transport. The reduced rate of water trans...

Mortality, growth, and grazing impact of a cohort of bivalve larvae, Mytilus edulis L.

Abstract A cohort of bivalve larvae, mainly Mytilus edulis, was followed during its residence in the plankton of the Isefjord, Denmark, and the mortality and growth of the larvae, as well as their grazing effects on the phytoplankton have been estimated. The pelagic stage lasted one month. The initial number of larvae was about 3000 · 1−1, and the daily mortality was about 13 %. The mean growth rate amounted to 13–16% of the body mass daily, and the net growth efficiency was 60 %. The cohort of bivalve larvae cleared 40–50 % of the surrounding water daily of small food particles, probably mostly flagellates. The phytoplankton production at the time the bivalve larvae appeared in the plankton was dominated by diatoms that were not accessible as food to the larvae. It is concluded that dense populations of bivalve larvae may exert heavy grazing pressures on the ultraplankton without directly affecting the populations and primary production of larger phytoplankton organisms.

Patterns of uptake of dissolved amino acids in mussels (Mytilus edulis)

Uptake of dissolved amino acids was measured in mussels adapted to 50% artificial sea water or to the sea water containing 2 mM glycine. In mussels adapted to amino-acid free sea water net uptake from μmolar solutions of glycine, glutamic acid, taurine, glutamine and tyrosine could be described by the Michaelis-Menten equation. Mussels adapted to 2 mM glycine exhibited more complex patterns of uptake that changed with time after transfer to μmolar solutions of glycine. It is suggested that the properties of the epidermal transport systems are adaptable, and that they are modified by the presence of amino acids in the medium, perhaps indirectly through changes in the concentrations of the intracellular pool of free amino acids. The uptake rates measured in mussels adapted to aminoacid free sea water express the maximum capacities for net uptake. In this state of adaptation, mussels that process the surrounding water at optimal rates may clear up to about half of the water passing the mantle cavity of amino acids present at concentrations of about 1 μM. Two thirds of 3H-taurine taken up was recovered in the gills, the remaining third was about equally distributed between the mantle and the rest of the body. There was no significant loss or redistribution of label within 24 h. It is concluded that the uptake of amino acids in the mussel gill is epidermal rather than transepidermal.

Urea and Amphibian Water Economy

Accumulation of urea in the body fluids enables some amphibians to tolerate high ambient salinities (Bufo viridis, Xenopus laevis, Rana cancrivora, Ambystoma tigrinum, Batrachoseps spp.) or to estivate in soil with low water potentials (Scaphiopus spp.). These species are assumed not only to accumulate urea produced in the normal metabolism, but to synthesize urea in response to water shortage. Re-examination of the data did not support the view of an osmoregulatory urea synthesis. Increased urea synthesis on exposure to high salinities in X. laevis, R. cancrivora and Batrachoseps spp. seemed to reflect reactions to an adverse environment. It is suggested that in amphibians, solute concentration in the plasma and rate of excretion of urea are coordinated so that at a certain plasma concentration, urea is excreted at the same rate at which it is produced. The higher the level of urea in the body fluids at balance between production and excretion, the higher the tolerance of the species of low external water potentials. The mechanisms that integrate the relationship between plasma solute concentration and handling of urea by the kidneys are not known.

Water processing in ciliary feeders, with special reference to the bivalve filter pump

Abstract 1. 1. Ciliary suspension feeders process the ambient water at low pressures of about 1 mm H2O. 2. 2. The resistance to unrestrained water flow in the mucus net filters of ascidians and a gastropod, as well as in the filters of ciliates, flagellates and sponges, amounts to about 0.1 mm H2O. 3. 3. Particle capture in most metazoan ciliary filter feeders, not employing mucus nets, does not seem to be based on mechanical interception of the particles, but the mechanisms are not well understood. 4. 4. Pressure and flow in the bivalve filter pump vary with the valve gape, and only the undisturbed, relaxed bivalve can fully exploit the pump capacity.

Amphibian respiration and olfaction and their relationships: from Robert Townson (1794) to the present

The present review examines the developments in the elucidation of the mechanisms of amphibian respiration and olfaction. Research in these two areas has largely proceeded along independent lines, despite the fact that ventilation of the nasobuccopharyngeal cavity is a basic element in both functions. The English naturalist Robert Townson demonstrated, in the 1790s, that amphibians, contrary to general belief, ventilated the lungs by a pressure‐pump mechanism. Frogs and other amphibians respire by alternatively dilating and contracting the buccopharyngeal cavity. During dilatation, with the mouth and glottis closed, air is sucked in through the open nostrils to fill the cavity. During contraction of the throat, with nostrils closed and glottis open, the air in the buccopharyngeal cavity is pressed into the lungs. During expiration, the glottis and nostrils open and air is expelled from the lungs ‘by their own contraction from a state of distention’. Herholdt (1801), a Danish army surgeon, independently described the buccal pressure‐pump mechanism in frogs, his experiments being confirmed by the commissioners of the SociétéPhilomatique in Paris. Haro (1842) reintroduced a suction mechanism for amphibian respiration, which Panizza (1845) refuted: excision of the tympanic membranes prevented lung inflation, the air in the buccopharyngeal cavity leaving through the tympanum holes. Closure of the holes with the fingers restored lung inflation. The importance of cutaneous respiration in frogs and other amphibians was discovered by Spallanzani (1803), who found that frogs might survive excision of the lungs and that the amounts of exhaled carbon dioxide were small compared with those eliminated through the skin. Edwards (1824) confirmed and extended Spallanzanis findings, and Regnault & Reiset (1849) attempted to establish the relative importance of skin and lungs as respiratory organs in frogs. The problem was solved by Krogh (1904a) who measured respiration through the skin and lungs separately and simultaneously. Krogh (1904a) confirmed that carbon dioxide was chiefly eliminated through the skin, correlated with its high diffusion rate in water and tissue, whereas the pattern of oxygen uptake varied seasonally, the pulmonary uptake being lower than the cutaneous during autumn and winter, but substantially higher during the breeding period. Dolk & Postma (1927) confirmed this respiratory pattern. More recently, Hutchison and coworkers have examined the relative role of pulmonary and cutaneous gas exchange in a large number of amphibians, equipped with head masks for the separate measurement of the lung respiration in normally ventilating animals (Vinegar & Hutchison, 1965; Guimond & Hutchison, 1968; Hutchison, Whitford & Kohl, 1968; Whitford & Hutchison, 1963, 1965, 1966). As early as 1758, Rösel von Rosenhof suggested that the lungs of frogs in water functioned as hydrostatic organs that permitted the animal to float at the surface or rest on the bottom of the pond. The suggestion was inspired by observations made in the second half of the seventeenth century by members of the Royal Academy of Sciences in Paris. The French anatomists demonstrated that a tortoise, presumably the European freshwater turtle Emys orbicularis, could regulate its buoyancy by changing the volume of the lungs, to descend passively or ascend in the water. The hydrostatic function of the lungs has been repeatedly rediscovered, by Emery (1869) in the frog, by Marcacci (1895) in frogs, toads and salamanders, by Whipple (1906b) in a newt, by Willem (1920, 1931) in frogs and Xenopus laevis, by Speer (1942) in several anurans and urodeles, and finally by de Jongh (1972) in Xenopus laevis. In the second half of the nineteenth century a number of important papers appeared which confirmed and extended Townsons (1794) and Panizzas (1845) analysis of the normal respiratory movements in frogs. Lung ventilation cycles,interspaced by oscillatory movements of the throat, might periodically be replaced by a sequence predominated by inspirations, resulting in lung inflation, followed by exhalations that restored normal lung volume. Babæk (1912a) established that inflations were reactions to the experimental manipulations, and that in resting, undisturbed frogs, lung ventilations normally occurred singly, interspaced by series of approximately 10–50 buccal oscillations. Extensive comparative studies early in the century showed that the respiratory mechanisms and patterns were basically similar in all anurans and urodeles investigated. The modern era of investigations in amphibian respiration began with the work of de Jongh & Gans (1969). They recorded pressures in the buccal cavity, lungs and visceral cavity and electrical activity of some 15 muscles possibly associated with respiration in the bullfrog Rana catesbeiana. The respiration recorded in the frogs was predominated by cycles of lung inflation and deflation, consistent with substantially but not excessively disturbed frogs. Studies by other investigators on various anuran species showed respiratory patterns that varied strongly with respect to the frequency and degree of lung inflations, presumably reflecting degrees to which the experimental conditions affected the breathing.

Role of urinary and cloacal bladders in chelonian water economy: Historical and comparative perspectives

The Parisian comparative anatomist Claude Perrault, dissecting an Indian giant tortoise in 1676, was the first to observe that the urinary bladder is of an extraordinary size in terrestrial tortoises. In 1799, the English comparative physiologist Robert Townson suggested that the bladder functioned as a water reservoir, as he had shown previously for frogs and toads. However, these observations went unnoticed in subsequent reports on tortoise water economy that were made by travellers and naturalists visiting the Galapagos Archipelago and marvelling over the huge numbers of giant tortoises that inhabited these desert-like islands. The first such report was by an American naval officer, David Porter, who was a privateer in the 1812-15 war with England. In his journal he referred to the constant supply of water which the Galapagos tortoises carried with them. References to the location in the body, as well as the amounts and quality of the water stored, were, however, contradictory. The confusion concerning the anatomical identity of the water reservoir in the Galapagos tortoise, Geochelone elephantopus, persisted throughout the nineteenth century, and continued when studies of tortoise water economy and drinking behaviour in arid environments were taken up independently in the desert tortoise, Gopherus agassizii, which inhabits the desert regions in the south-western United States. In 1881 Cox found large sacs filled with clear water under the carapace, but it was half a century later that these sacs were identified as the large bilobed bladder; references to specific water sacs continued to appear in the literature until the 1960s. Since 1970, information on the water economy of desert tortoises has been obtained from extensive field studies. Rates of disappearance of tritiated water injected into the body have shown that during the drought periods of the summer, water turnover (intake) rates do not differ from the rates of metabolic water production. Under these conditions urine is not voided, but is stored in the large bladder. During a drought period the bladder urine increases from initially low osmolality finally to reach isosmolality with the blood plasma. Soluble K+ is the major cation of the urine, but large amounts of K+ are also present as precipitated urates. During a drought period the body is in negative water balance, but despite substantial losses of total body water, the plasma concentrations of Na+ and Cl- can remain constant for many months, indicating regulation of the extracellular fluid and water content of the body tissues by reabsorption of water from the urinary bladder. The bladder thus acts both as a store for nitrogenous waste and K+ and as a water reservoir during droughts. Following rain showers, there is a sharp decline in tritium activity correlated with copious drinking from temporary pools of rain water. The old bladder urine is voided and most of the water drunk is stored as a highly dilute urine. In 1676 Perrault observed that in a freshwater turtle, Emys orbicularis, but not in the giant tortoise, two other bladders opened into the cloaca. By the mid-twentieth century it had been established that these cloacal bladders typically were restricted to species of chelonians that led a semi-terrestrial or semi-aquatic life. The function of the bladders has been debated since Townson observed in 1799 that dehydrated freshwater turtles took up water by anal drinking, suggesting that anal drinking served in the water economy of semi-terrestrial turtles. Since then, the bladders have been ascribed hydrostatic and respiratory functions, but the recent literature mostly argues for a respiratory function. The possible role of the cloacal bladders as a water reservoir in amphibious turtles is still open. Terrestrial amphibians and tortoises are unique among vertebrates in possessing large urinary bladders that may function as water reservoirs in dry environments. (ABSTRACT TRUNCATED)

Role of pars nervosa of the hypophysis in amphibian water economy: A re-assessment

1. Responses in renal function and in water permeability of skin and bladder to wet and dry environments are accomplished within the range of normal hydration of the amphibian organism. 2. Urine production is discontinued at moderate dehydration. 3. Strong dehydration is needed to raise plasma arginine vasotocin (AVT). 4. Surgical interference with hypophysial function may repress water balance responses because of pars distalis dysfunction, with no clear effect of elimination of pars nervosa function. 5. Antidiuretic hormones, along with adrenergic agonists, may be potent stimulators of the water permeability of membranes of variable permeability, such as skin of terrestrial anurans. 6. AVT does not play a key role in amphibian water economy, but may exert a modulatory role in the control of renal function, secondary to nervous control.