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Effect of saline acclimation on duodenum, jejunum, and ileum mass and length expressed as mean residual values ± SE (, FW females; , SW females; , FW males; , SW males). P values for ANOVA of residuals are given in Table 5. FW, tap (fresh) water; SW, salt water.
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Ducks absorb imbibed Na+ and water in the anterior gut and reabsorb Na+ and water from urine refluxed into the hind gut. In Mallards (Anas platyrhynchos) this process is sexually disparate: males reflux and reabsorb more water, mainly in the ceca. We examined the effect of saline acclimation on the size of Mallard organs, especially the gut and oth...
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... mass, duodenum length, and jejunum mass were unaffected by saline acclimation in either sex (Table 5, Fig. 3), but saline acclimation increased jejunum length in males (P < 0.005; Table 5, Fig. 3). Ileum mass and length did not differ between FW males and FW females. After saline acclimation, the ileum was heavier (P < 0.02) and longer (P < 0.03) in both sexes (Table 5, Fig. 3). Overall, following saline acclimation, the small intestine was ...
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... mass, duodenum length, and jejunum mass were unaffected by saline acclimation in either sex (Table 5, Fig. 3), but saline acclimation increased jejunum length in males (P < 0.005; Table 5, Fig. 3). Ileum mass and length did not differ between FW males and FW females. After saline acclimation, the ileum was heavier (P < 0.02) and longer (P < 0.03) in both sexes (Table 5, Fig. 3). Overall, following saline acclimation, the small intestine was signifi- cantly longer (P < 0.02) in males but not in females, while its mass was little ...
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... jejunum mass were unaffected by saline acclimation in either sex (Table 5, Fig. 3), but saline acclimation increased jejunum length in males (P < 0.005; Table 5, Fig. 3). Ileum mass and length did not differ between FW males and FW females. After saline acclimation, the ileum was heavier (P < 0.02) and longer (P < 0.03) in both sexes (Table 5, Fig. 3). Overall, following saline acclimation, the small intestine was signifi- cantly longer (P < 0.02) in males but not in females, while its mass was little affected in either sex (Table ...
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... drinking-water salinity (Hughes 1983). Acclimation to sa- line does not affect the rate of Na uptake in the gut of ducks ( Hughes and Roberts 1988), therefore large amounts of wa- ter and Na cross the gut wall of SA ducks. This affects some gut segments more than others. In four of the gut segments (esophagus and proventriculus (Fig. 2), jejunum (Fig. 3), and ceca (Fig. 4)), drinking saline affected males and females differently. In the anterior gut the changes were greater in females. The esophagus was lengthened and proventriculus mass and length were decreased only in females (Fig. 2). We can offer no insight into the particular sensitivity of the ante- rior gut of females to Na ...
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... only in females (Fig. 2). We can offer no insight into the particular sensitivity of the ante- rior gut of females to Na intake. To our knowledge, Na and water transport in the anterior gut has not been measured in birds. Changes in the small intestine were greater in males. Saline acclimation increased the length of the jejunum only in males (Fig. 3). While saline acclimation increased ileum mass in both sexes, it increased ileum length only in males (Fig. 3). These segments are known to be important in Na and water uptake. Exposing Pekin ducklings to 60% seawa- ter roughly doubled water and Na transport in the jejunum (Crocker and Holmes 1971). The water and Na transport ca- ...
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... females to Na intake. To our knowledge, Na and water transport in the anterior gut has not been measured in birds. Changes in the small intestine were greater in males. Saline acclimation increased the length of the jejunum only in males (Fig. 3). While saline acclimation increased ileum mass in both sexes, it increased ileum length only in males (Fig. 3). These segments are known to be important in Na and water uptake. Exposing Pekin ducklings to 60% seawa- ter roughly doubled water and Na transport in the jejunum (Crocker and Holmes 1971). The water and Na transport ca- pacity of the ileum remained high in saline acclimated adult Pekin ducks ( Skadhauge et al. 1984). Among Pekin ...
Citations
... The enlargement and modification of cephalic glands for salt excretion have significant advantages (e.g., contrary to kidneys, their activity can stop when not demanded, Withers, 1992). However, they also require two main changes: first, cephalic glands need extra free space to be housed and cannot be enclosed by rigid walls as they greatly change their volume even in few hours (Hughes, Bennett, & Sullivan, 2002;Peaker & Linzell, 1975); second, when salt glands excrete in the air like birds and marine iguanas, they need a mechanism to avoid encrustation blocking the ducts (Withers, 1992). Extant sauropsids with nasal salt glands resolve the first problem by displacing the main body of the glands backward above the orbits as in birds (Marples, 1932;Schmidt-Nielsen & Fange, 1958) or by broadening the nasal region as in iguanas (Hazard, 2001;Peaker & Linzell, 1975). ...
The evolution of Thalattosuchia documents the unique shift among Crocodylomorpha from aquatic continental/coastal habitats to a fully pelagic lifestyle. This transition was coupled with deep modification of their skeletons, such as hydrofoil forelimbs, hypocercal tail, and loss of osteoderms. The natural snout casts of the rhacheosaurin Cricosaurus araucanensis showed that it also included changes in the internal anatomy of the snout like the enlargement of nasal glands (probably for salt excretion) and the rearrangement of the paranasal sinus system, including the internalization of the antorbital sinus. Here we described the snout natural cast of the geosaurin Dakosaurus andiniensis from the Late Jurassic of Patagonia. The information provided by it indicates that, despite having different external morphologies and ecology, D. andiniensis and C. araucanensis share the same facial anatomy. The new cast preserves a suborbital diverticulum of the antorbital sinus protruding into the orbit through the postnasal fenestra. Its location indicates that it was interleaved with jaw adductor muscles suggesting an active airflow in the paranasal sinus. We provide a putative functional interpretation of this peculiar arrangement where bellow pumps actions of musculature may help drain salt glands. The rearrangement of the paranasal sinuses predates the transition to a completely pelagic‐lifestyle. We proposed a stepwise evolutionary scenario of Thalattosuchia, implying changes in the preorbital region (and orbit orientation) where the internalized antorbital sinus via its subsidiary diverticulum was co‐opted for helping nasal glands drainage. Further scrutiny of facial anatomy of a larger sample of thalattosuchians will help to test this hypothesis.
... Salt intake can increase the mass of intestines (Hughes et al., 2002), increase gut water and sodium uptake rates in mallards (Crocker and Holmes, 1971) and decrease the time required for fluid to move through the gut (Roberts and Hughes, 1984). The hindgut appears to be particularly important for osmoregulation when saltglands are exposed to high salt loads because the hindgut can maintain high rates of intestinal salt and water reabsorption during salt loading, routing the salt to the saltglands for excretion and thereby retrieving "free water" (Schmidt-Nielsen et al., 1963;Laverty and Skadhauge, 2008;McWhorter et al., 2009). ...
During the course of their lives many vertebrates live and forage in environments characterized by different salinities and must therefore respond to changes in salt intake. This is particularly true for numerous species of migratory waterbirds, especially those that routinely commute between saltwater and freshwater wetlands throughout their annual cycle and/or within a season. These birds have evolved a suite of morphological, physiological and behavioural mechanisms to successfully maintain osmoregulatory balance. However, relatively little is known about the impacts of salinity on the distribution, physiological performance and reproductive success of waterbirds. Here I review the current knowledge of the physiological and behavioural mechanisms through which waterbirds cope with contrasting salinities and how some of the adjustments undertaken might interfere with relevant aspects of their performance. I argue that, because of their strong reliance on wetland ecosystems for foraging and breeding, waterbirds may be particularly vulnerable to climate-induced changes in salinity, especially in arid or semiarid tropical areas where increases in both temperature and salinity may affect their body condition and, ultimately, survival prospects. I conclude by offering some suggestions for future research that could take us beyond our current level of understanding of avian osmoregulation.
... A similar case has been reported in ducklings of the mallard Anas platyrhynchos for which adaptive growth and differentiation of salt glands occur in acclimated ducklings compared to naive animals (HILDEBRANDT, 2001). HUGHES et al. (2002) showed that drinking saline affected male and female mallards differently regarding the increase of salt glands, ileum and ceca. The ability to cope with excessive ionic sodium and chloride seemingly does not depend on age in Audouin's gull, contrary to that reported for non seabird species (FUDGE, 2000), because a large number of chicks (n=183) of Audouin's gull reared by us with freshwater during their early stages of development and with marine water later on did not show any symptoms resembling salt poisoning. ...
... A similar case has been reported in ducklings of the mallard Anas platyrhynchos for which adaptive growth and differentiation of salt glands occur in acclimated ducklings compared to naive animals (HILDEBRANDT, 2001). HUGHES et al. (2002) showed that drinking saline affected male and female mallards differently regarding the increase of salt glands, ileum and ceca. The ability to cope with excessive ionic sodium and chloride seemingly does not depend on age in Audouin's gull, contrary to that reported for non seabird species (FUDGE, 2000), because a large number of chicks (n=183) of Audouin's gull reared by us with freshwater during their early stages of development and with marine water later on did not show any symptoms resembling salt poisoning. ...
... liver, gizzard and intestines, Dolnik and Blyumental 1967, Gauthier et al. 1984, Hume and Biebach 1996, Jehl 1997 or locomotory structures (Marsh 1984) was generally less well accepted as an evolutionary adaptation to the conflicting needs of life history events, than have changes in fat depots. For one thing, changes in the morphology and size of digestive organs may merely reflect diet, since birds exploiting high quality diets generally support smaller digestive organs and liver (Moss 1972, 1974, Miller 1975, Kehoe and Ankney 1985, Hughes et al. 2002. However, recent evidence suggests that long distance migrants may construct, dispense with and rebuild some body struc- tures before prolonged flight to reduce flight costs (Piersma and Gill 1998). ...
The “cost-benefit” hypothesis states that specific body organs show mass changes consistent with a trade-off between the importance of their function and cost of their maintenance. We tested four predictions from this hypothesis using data on non-breeding greylag geese Anser anser during the course of remigial moult: namely that (i) pectoral muscles and heart would atrophy followed by hypertrophy, (ii) leg muscles would hypertrophy followed by atrophy, (iii) that digestive organs and liver would atrophy followed by hypertrophy and (iv) fat depots be depleted. Dissection of geese captured on three different dates during wing moult on the Danish island of Saltholm provided data on locomotory muscles and digestive organ size that confirmed these predictions. Locomotory organs associated with flight showed initial atrophy (a maximum loss of 23% of the initial pectoral muscle mass and 37% heart tissue) followed by hypertrophy as birds regained the powers of flight. Locomotory organs associated with running (leg muscles, since geese habitually run to the safety of water from predator-type stimuli) showed initial hypertrophy (a maximum gain of 37% over initial mass) followed by atrophy. The intestines and liver showed initial atrophy (41% and 37% respectively), consistent with observed reductions in daily time spent feeding during moult, followed by hypertrophy. The majority of the 22% loss in overall body mass (mean 760 g) during the flightless period involved fat utilisation, apparently consumed to meet shortfalls between daily energetic needs and observed rates of exogenous intake. The results support the hypothesis that such phenotypic plasticity in size of fat stores, locomotor and digestive organs can be interpreted as an evolutionary adaptation to meet the conflicting needs of the wing moult.
... Males may have higher water and Na intake (Bennett et al. 2000), particularly following ligation of the intestinal ceca (Hughes et al. 1991), yet void a smaller volume of more concentrated cloacal fluid (Hughes et al. 1992). Among Mallards, A. platyrhynchos, the progenitors of domestic Pekin ducks (Bo 1988), osmoregulatory organ masses do not differ between the sexes, but the effect of saline intake is sexually disparate for some organs (Hughes et al. 2002). Male Mallards showed greater hypertrophy of the salt glands, jejunum, ileum, ceca, and possibly the kidneys, while the proventriculus became shorter only in females. ...
... Breeding selection also affected organ masses. For example, relative kidney mass does not differ between male and female Mallards (Hughes et al. 2002), but kidneys are much larger in female Pekin ducks (Hughes et al. 1995) and females tolerate saline better than males do (Hughes et al. 1992). This suggests that osmoregulatory organs other than the kidneys might also be larger in female Pekin ducks and contribute to their greater salt tolerance. ...
... To test these hypotheses, we retrospectively examined relative organ masses of freshwater-(FW) and salineacclimated (SA) Pekin ducks collected at the termination of previous experiments in this laboratory and compared them with those of FW and SA Mallards (Hughes et al. 2002). ...
Osmoregulatory organ masses of freshwater Mallards (Anas platyrhynchos) do not differ between the sexes, but drinking saline induces changes that are sexually disparate in some organs. We examined relative size of organ masses of male and female Pekin ducks (that were domesticated from Mallards) and compared their responses to saline intake with those of Mallards. Organ masses of male and female Mallards do not differ in size. The liver and kidneys are heavier in female Pekin ducks and their digestive tract (except for the proventriculus and duodenum) is longer and heavier; male Pekin ducks have heavier salt glands. Mallards acclimated to saline drinking water have enlarged salt glands but not kidneys, adrenal glands, or Harderian glands, their proventriculus tends to be shorter and lighter, the jejunum longer in males, and the ileum longer and heavier in both sexes. In Pekin ducks that drink saline, the salt and Harderian glands are larger and their kidneys (but not adrenal glands) tend to be larger; the proventriculus is unaffected, but the small intestine is lighter, but not shorter, in females. Body, salt gland, Harderian gland, ventriculus, and duodenum masses vary seasonally in Pekin ducks. Discussion considers the effects of season and sex on relative organ masses and how saline-induced changes in them reflect domestication and may influence salt tolerance.
Dietary salt intake in domestic fowl affects epithelial transport and morphology of the lower intestine (colon and coprodeum). This study investigated lower intestinal morphology and transport activity in two wild bird species with natural diets containing either low or high salt. Tissues from rock ptarmigan (Lagopus mutus) and common murres (Uria aalge) were sampled for histology and electrophysiological analyses. The ptarmigan exists on a low salt diet, while the murre lives on a high protein and high salt diet. The ptarmigan colon and coprodeum had villi/folds and crypts and the epithelium contained absorptive epithelial cells, mitochondria-rich cells and goblet cells. The colon had significant amiloride-inhibitable Isc, 5-15 μA/cm2, with no glucose-stimulated Isc, and no significant phloridzin inhibition. The coprodeum also had high amiloride-inhibitable Isc. This transport pattern corresponded to that of chickens on low-salt diets. However, the ptarmigan colon also had a significant lysine/leucine-stimulated Isc of 3 ± 1.0 μA/cm2. The short U. aalge colon was similar to that of ptarmigans, but with no villi. It demonstrated a significant lysine/leucine-stimulated Isc (11 ± 3.5 μA/cm2) with no amiloride-inhibitable Isc, similar to the high-salt chicken colon, but with no Na+-glucose cotransport. The murre coprodeum was inert to all substances and showed high resistance (1000 Ω·cm2), with a multilayered squamous epithelium. Despite some variations possibly associated with dietary protein intake, we conclude that natural high and low salt diets in different avian species are associated with different lower intestinal transport patterns, providing for post-renal adjustments in ion and water excretion.
Marine birds can drink seawater because their cephalic 'salt' glands secrete a sodium chloride (NaCl) solution more concentrated than seawater. Salt gland secretion generates osmotically free water that sustains their other physiological processes. Acclimation to saline induces interstitial water and Na move into cells. When the bird drinks seawater, Na enters the plasma from the gut and plasma osmolality (Osm(pl)) increases. This induces water to move out cells expanding the extracellular fluid volume (ECFV). Both increases in Osm(pl) and ECFV stimulate salt gland secretion. The augmented intracellular fluid content should allow more rapid expansion of ECFV in response to elevated Osm(pl) and facilitate activation of salt gland secretion. To fully utilize the potential of the salt glands, intestinally absorbed NaCl must be reabsorbed by the kidneys. Thus, Na uptake at gut and renal levels may constrain extrarenal NaCl secretion. High NaCl intake elevates plasma aldosterone concentration of Pekin ducks and aldosterone stimulates intestinal and renal water and sodium uptake. High NaCl intake induces lengthening of the small intestine of adult Mallards, especially males. High NaCl intake has little effect on glomerular filtration rate or tubular sodium Na uptake of birds with competent salt glands. Relative to body mass, kidney mass and glomerular filtration rate (GFR) are greater in birds with salt glands than in birds that do not have them. Birds with salt glands do not change GFR, when they drink saline. Thus, their renal filtrate contains excess Na that is, in some species, almost completely renally reabsorbed and excreted in a more concentrated salt gland secretion. Na reabsorption by kidneys of other species, like mallards is less complete and their salt glands make less concentrated secretion. Such species may reflux urine into the hindgut, where additional Na may also be reabsorbed for extrarenal secretion. During exposure to saline, marine birds maintain elevated aldosterone levels despite high Na intake. Marine birds are excellent examples of physiological plasticity.
