Osmoregulation in Birds

Skadhauge, Erik

doi:10.1007/978-3-642-81585-0

Cited by 196 publications

(113 citation statements)

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“…A retrograde uric acid transport (''urinary reflux'') from the cloaca to the caeca has been suggested for various bird species, including Emus (Skadhauge 1981, Braun and Campbell 1989, Laverty and Skadhauge 2008. The anatomy of Rheas and Emus, with their comparatively short colons, seems to facilitate such a mechanism, whereas its presence seems unlikely in Ostriches due to their long colon (Skadhauge et al 1984) and to date has not been demonstrated using contrast medium studies in Ostriches (Duke et al 1995).…”

Section: Discussionmentioning

confidence: 99%

Comparative digesta retention patterns in ratites

Frei

Ortmann

Reutlinger³

et al. 2015

The Auk

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Ratites differ distinctively in the anatomy of their digestive tract. For example, Ostriches (Struthio camelus) have a particularly long, voluminous colon and long paired caeca, Rheas (Rhea spp.) are characterised by a short colon with particularly prominent paired caeca, and Emus (Dromaius novaehollandiae) -have neither very prominent caeca nor a prominent colon. We tested whether digesta excretion patterns corresponded to these differences in anatomy, expecting Ostriches to have the longest and Emus the shortest digesta retention times, and Rheas possibly showing a selective retention of fluids observed in other birds and mammals with prominent caeca. We used 6 Ostriches (97-123kg), 5 Greater Rheas (R. americana, 22-27kg) and 2 Emus (32-34kg) fed a common diet of alfalfa pellets ad libitum in captivity. Intake per unit of metabolic body mass did not differ between Ostriches and Rheas but was significantly higher in Emus, which also displayed higher defecation frequencies and lower fiber digestibility. Mean digesta retention time for small fiber particles (2 mm) differed significantly among species ; Emu: 1.3-1.8h), but there were no differences between the retention of 2 mm or 8 mm particles or a solute marker within species. The shape of the marker excretion curves corresponded to digesta mixing in the digestive tract of Ostriches and Rheas but not Emus. The calculated dry matter gut fill (% of body mass) was significantly higher in Ostriches (1.6-1.8) than Rheas (0.3-1.0) and Emus (0.2). Ostriches had the highest, and Emus the lowest fecal dry matter concentration. These physiological findings match the differences in digestive anatomy and support the concept that in ratites, herbivory -and hence flightlessness -evolved repeatedly in different ways. ABSTRACT Ratites differ distinctively in the anatomy of their digestive tracts. For example, Common Ostriches (Struthio camelus, hereafter Ostriches) have a particularly long, voluminous colon and long, paired caeca; Rheas (Rhea spp.) are characterized by a short colon with particularly prominent paired caeca; and Emus (Dromaius novaehollandiae) have neither prominent caeca nor a prominent colon. We tested whether digesta excretion patterns corresponded to these differences in anatomy, expecting Ostriches to have the longest and Emus the shortest digesta retention times, and Rheas possibly showing a selective retention of fluids observed in other birds and mammals with prominent caeca. We used 6 Ostriches (97-123 kg), 5 Greater Rheas (R. americana, 22-27 kg), and 2 Emus (32-34 kg) fed a common diet of alfalfa pellets ad libitum in captivity. Intake per unit of metabolic body mass did not differ between Ostriches and Greater Rheas but was significantly higher in Emus, which also displayed higher defecation frequencies and lower fiber digestibility. Mean digesta retention time for small fiber particles (2 mm) differed significantly among species (Ostrich: 30-36 h; Greater Rhea: 7-19 h; Emu: 1.3-1.8 h), but there were no differences between the retention o...

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Section: Discussionmentioning

confidence: 99%

Comparative digesta retention patterns in ratites

Frei

Ortmann

Reutlinger³

et al. 2015

The Auk

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“…In an analogous fashion, the salt gland of many birds can increase in size and Na + ,K + -ATPase content in response to environmental salinity (Skadhauge, 1981). These salinity-induced changes apparently require an intact hypophysio-adrenocortical axis, though the role of corticosteroids appears to be permissive.…”

Section: Article In Press 7 January 2006 Disk Used Jaya (Ce) / Prabakmentioning

confidence: 99%

Hormonal control of salt and water balance in vertebrates

McCormick¹,

Bradshaw

2006

General and Comparative Endocrinology

257

149

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The endocrine system mediates many of the physiological responses to the homeostatic and acclimation demands of salt and water transport. Many of the hormones involved in the control of salt and water transport are common to all vertebrates, although their precise function and target tissues have changed during evolution. Arginine vasopressin (vasotocin), angiotensin II, natriuretic peptides, vasoactive intestinal peptide, urotensin II, insulin and non-genomic actions of corticosteroids are involved in acute (minutes and hours) alterations in ion and water transport. This rapid alteration in transport is primarily the result changes in behavior, blood Xow to osmoregulatory organs, and membrane insertion or activation (e.g., phosphorylation) of existing transport proteins, ion and water channels, contransporters and pumps. Corticosteroids (through genomic actions), prolactin, growth hormone, and insulin-like growth factor I primarily control long-term (several hours to days) changes in transport capacity that are the result of synthesis of new transport proteins, cell proliferation, and diVerentiation. In addition to the important task of establishing broad evolutionary patterns in hormones involved in ion regulation, comparative endocrinology can determine species and population level diVerences in signaling pathways that may be critical for adaptation to extreme or rapidly changing environments.  2006 Published by Elsevier Inc.Keywords: Osmoregulation; Vertebrates; Ion transport; AVP; AVT; ANP; Angiotensin; Aldosterone; Cortisol; Growth hormone; Prolactin; IGF-I Physiological requirements for salt and water transportMaintenance of constant intracellular and extracellular ionic and osmotic environment (Bernard's constancy of 'le milieu intérieur') is critical for the normal functioning of cells. With several notable exceptions, such as hagWsh, sharks and ureotelic marine frogs, the majority of vertebrates maintain a remarkably similar salt content of their extracellular Xuid, approximately one-third that of seawater. This basic strategy results in diVerent transport demands for vertebrates depending on their external environment. In fresh water environments vertebrates must actively take up salts, whereas in seawater they must secrete excess salts. In terrestrial environments vertebrates must conserve water. The demands for ion and water transport can vary greatly, depending on both internal factors such as metabolic rate, and external factors such as salinity or water availability.Hormones play a critical role in signaling and controlling the homeostatic and acclimation demands of salt and water transport (Bentley, 1998). In spite of the diVerences in transport needs and capabilities among vertebrates (and even the organs responsible for ion transport) many of the hormones involved are remarkably similar. In addition to acting on the basic mechanisms of ion transport, natural selection will act on the underlying neuroendocrine controls. Our understanding of large evolutionary trends (e.g., evolution of...

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“…Before the cannula was introduced into the cloaca, each pigeon was given 1 ml of water; this is equal to the water requirement of a pigeon for 1 hour (Skadhauge, 1981).…”

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confidence: 99%

“…Bokori et al (1965) and Sykes (1971) found, as in this experiment, a large variation in the various ion concentrations in urine. It is well known that large quantities of cations are trapped in uric acid precipitates (McNabb andMcNabb, 1975,1977;Skadhauge, 1981). The degree of 'cation trapping' varies from 3 to 75% for Na + , 8 to 84% for K + and 17 to 32% for Ca 2+ and Mg 2+ .…”

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confidence: 99%

“…The degree of 'cation trapping' varies from 3 to 75% for Na + , 8 to 84% for K + and 17 to 32% for Ca 2+ and Mg 2+ . This variation is caused by differences in hydration, the protein and salt percentages of the food, the species and a possible influence of storage in the cloaca (Skadhauge, 1981). Furthermore the Cr level in the urine mainly depends on the concentration of sodium chloride in the food (Skadhauge and Schmidt-Nielsen, 1967).…”

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