Effect of saline intake on osmotic homeostasis in ducks
Salinity appears to be an important barrier to habitat selection by ducks, yet little is known about the osmoregulatory abilities of ducks that use saline environments. This thesis examines the physiological mechanisms by which ducks maintain osmotic balance when exposed to saline. I first used d...
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2009
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Online Access: | http://hdl.handle.net/2429/13306 |
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Salinity appears to be an important barrier to habitat selection by ducks, yet little is
known about the osmoregulatory abilities of ducks that use saline environments. This
thesis examines the physiological mechanisms by which ducks maintain osmotic balance
when exposed to saline. I first used domesticated Pekin ducks (Anas platyrhynchos) as a
model to identify the osmoregulatory traits that confer saline tolerance in ducks. I then
compared these in wild species selected to represent ducks that utilize freshwater,
estuarine and marine habitats: Mallards (Anasplatyrhynchos), Canvasbacks (Aythya
valisineria) and Barrow's Goldeneyes (Bucephala islandica), respectively. My major
hypothesis is that among the three species of wild ducks, the ability to maintain osmotic
homeostasis during acclimation to saline, habitat affinity, and their ability to secrete
excess Na+ are correlated.
When Pekin ducks were given increasing concentrations of saline to drink, they
maintained water and osmotic balance at salinities up to 300 mM NaCl by producing salt
gland secretion slightly higher than 300 mM Na+ . This concentration is roughly half that
produced in response to intravenous saline infusion (500-600 mM Na+ ) . When the three
species of wild ducks were similarly acclimated to saline, Canvasbacks and Goldeneyes
were both more saline tolerant than Pekin ducks and maintained water balance at
salinities equivalent to full strength seawater. Mallards did not tolerate salinities greater
than 225 mM NaCl . Evaluation o f the relationship between maximum saline tolerance
and maximum concentrating ability of the salt glands could not be tested because ducks
did not secrete spontaneously when handled.
Pekin ducks acclimated to 300 mM NaCl move extracellular water and Na+ into the
cells, a mechanism that may be important to the ability to initiate salt gland secretion. I
then examined the relative roles of extracellular fluid volume and concentration in the
stimulation of salt gland secretion. Increases in extracellular fluid volume and
concentration worked interactively to stimulate salt gland secretion. Ducks with a small
initial extracellular fluid volume took longer to initiate salt gland secretion and secreted
less of the imposed saline load than ducks with a larger extracellular fluid volume. Initial
volume of extracellular fluid and its expansion in response to saline loading may be the
dominant determinants of the secretory response. The results obtained from the Pekin
duck experiments showed that redistribution of extracellular water and Na+ might be
important in the control of salt gland secretion and in conferring tolerance to saline in
ducks. When wild ducks drank freshwater, total volume of body water did not differ
among the three species, but Goldeneyes, the most marine species, had the largest
extracellular fluid volume and was the only species that shifted water and Na+ into the
cells in response to saline acclimation.
The last study examined kidney and salt gland functions by which wild ducks eliminate
excess Na+ , but maintain water balance. I found that renal filtration was unaffected by
saline intake in any of the three species, but saline tolerance was determined by rates of
renal tubular water and Na+ reabsorption and salt gland Na+ secretion. Goldeneyes had the
highest rates of all these processes and were the only species that secreted all the infused
Na+ via the salt glands. Mallards had lower rates, although saline acclimated Mallards
eliminated all the infused Na+ by combined renal and extrarenal excretion. Canvasbacks
tolerated higher drinking water salinities than Mallards, even though their renal and
extrarenal Na+ excretion rates during acute saline loading indicated they should not be able
to do so. This suggests osmoregulation in Canvasbacks may involve Na+ and water
regulation at other sites, such as the gut. Postrenal modification o f urine may play an
important role in conservation of water in Canvasback. |
author |
Bennett, Darin Chris |
spellingShingle |
Bennett, Darin Chris Effect of saline intake on osmotic homeostasis in ducks |
author_facet |
Bennett, Darin Chris |
author_sort |
Bennett, Darin Chris |
title |
Effect of saline intake on osmotic homeostasis in ducks |
title_short |
Effect of saline intake on osmotic homeostasis in ducks |
title_full |
Effect of saline intake on osmotic homeostasis in ducks |
title_fullStr |
Effect of saline intake on osmotic homeostasis in ducks |
title_full_unstemmed |
Effect of saline intake on osmotic homeostasis in ducks |
title_sort |
effect of saline intake on osmotic homeostasis in ducks |
publishDate |
2009 |
url |
http://hdl.handle.net/2429/13306 |
work_keys_str_mv |
AT bennettdarinchris effectofsalineintakeonosmotichomeostasisinducks |
_version_ |
1716652717654409216 |
spelling |
ndltd-LACETR-oai-collectionscanada.gc.ca-BVAU.2429-133062014-03-14T15:46:53Z Effect of saline intake on osmotic homeostasis in ducks Bennett, Darin Chris Salinity appears to be an important barrier to habitat selection by ducks, yet little is known about the osmoregulatory abilities of ducks that use saline environments. This thesis examines the physiological mechanisms by which ducks maintain osmotic balance when exposed to saline. I first used domesticated Pekin ducks (Anas platyrhynchos) as a model to identify the osmoregulatory traits that confer saline tolerance in ducks. I then compared these in wild species selected to represent ducks that utilize freshwater, estuarine and marine habitats: Mallards (Anasplatyrhynchos), Canvasbacks (Aythya valisineria) and Barrow's Goldeneyes (Bucephala islandica), respectively. My major hypothesis is that among the three species of wild ducks, the ability to maintain osmotic homeostasis during acclimation to saline, habitat affinity, and their ability to secrete excess Na+ are correlated. When Pekin ducks were given increasing concentrations of saline to drink, they maintained water and osmotic balance at salinities up to 300 mM NaCl by producing salt gland secretion slightly higher than 300 mM Na+ . This concentration is roughly half that produced in response to intravenous saline infusion (500-600 mM Na+ ) . When the three species of wild ducks were similarly acclimated to saline, Canvasbacks and Goldeneyes were both more saline tolerant than Pekin ducks and maintained water balance at salinities equivalent to full strength seawater. Mallards did not tolerate salinities greater than 225 mM NaCl . Evaluation o f the relationship between maximum saline tolerance and maximum concentrating ability of the salt glands could not be tested because ducks did not secrete spontaneously when handled. Pekin ducks acclimated to 300 mM NaCl move extracellular water and Na+ into the cells, a mechanism that may be important to the ability to initiate salt gland secretion. I then examined the relative roles of extracellular fluid volume and concentration in the stimulation of salt gland secretion. Increases in extracellular fluid volume and concentration worked interactively to stimulate salt gland secretion. Ducks with a small initial extracellular fluid volume took longer to initiate salt gland secretion and secreted less of the imposed saline load than ducks with a larger extracellular fluid volume. Initial volume of extracellular fluid and its expansion in response to saline loading may be the dominant determinants of the secretory response. The results obtained from the Pekin duck experiments showed that redistribution of extracellular water and Na+ might be important in the control of salt gland secretion and in conferring tolerance to saline in ducks. When wild ducks drank freshwater, total volume of body water did not differ among the three species, but Goldeneyes, the most marine species, had the largest extracellular fluid volume and was the only species that shifted water and Na+ into the cells in response to saline acclimation. The last study examined kidney and salt gland functions by which wild ducks eliminate excess Na+ , but maintain water balance. I found that renal filtration was unaffected by saline intake in any of the three species, but saline tolerance was determined by rates of renal tubular water and Na+ reabsorption and salt gland Na+ secretion. Goldeneyes had the highest rates of all these processes and were the only species that secreted all the infused Na+ via the salt glands. Mallards had lower rates, although saline acclimated Mallards eliminated all the infused Na+ by combined renal and extrarenal excretion. Canvasbacks tolerated higher drinking water salinities than Mallards, even though their renal and extrarenal Na+ excretion rates during acute saline loading indicated they should not be able to do so. This suggests osmoregulation in Canvasbacks may involve Na+ and water regulation at other sites, such as the gut. Postrenal modification o f urine may play an important role in conservation of water in Canvasback. 2009-09-29T20:09:30Z 2009-09-29T20:09:30Z 2002 2009-09-29T20:09:30Z 2002-11 Electronic Thesis or Dissertation http://hdl.handle.net/2429/13306 eng UBC Retrospective Theses Digitization Project [http://www.library.ubc.ca/archives/retro_theses/] |