amounts of water through cloacal and extrarenal channels (BENTLEY, BRETZ, and
ScHMIDT-NIELSEN, 1967a).
The normal rates of urine flow differ considerably in different reptiles (Table 5.4)
and can vary from amounts equivalent to about 0.5% of the body weight in Malaclemys kept in sea-water, to 6% in the gecko lizard and 9% in the caiman when
kept in air. Water loss from the kidney and gut can constitute an avenue of water
loss, which in circumstances when such supplies are restricted, may be physiologically critical. Reptiles, unlike mammals and birds, cannot form a urine that is hyperosmotic to their body fluids and so cannot conserve water by increasing urine concentration in this way. However, some do have the ability to convert increased
amounts of their waste nitrogen into uric acid, which requires less water for its renal
excretion than the alternative products, ammonia and urea. The desert tortoise,
Table 5.4 Variations in the urine {low of reptiles in different states of hydration
mllkg hr
Normal Dehydrated Water loaded Saline loaded
Habitat
Crocodilia
Caiman scleropss
a) In fresh water
b) In air
3.5
1.1
Aquatic
Varies with vasotocin injections
1.3
Aprox.
Anuric
1.0
0.2
2.0
Aprox.
Anuric
0.9 to
Desert
Anuric
2.4
Desert
0.6
Wet
tropical
Anuric
Semidessert
Aquatic
Chelonia
Pseudemys scripta 2
(Slider turtle)
Malacl emys centratas
(Diamondback terrapin)
a) In fresh water
b) In sea-water
Gopherus agassizii»
(Desert tortoise)
Lacertilia
Hemidactylus Sp.4
(Gecko)
Phrynosoma cornutumi
(Horned toad)
Trachysaurus rugosus 5
(Bobtail lizard)
Ophidia
N atrix sipedon':
(Water snake)
2.6
2.0
0.24
1.3
0.8
Anuric
3.6
8.3
12.1
1.8
11.3
0.4 to
Anuric
Aquatic
Estuarine
IBENTLEY and SCHMIDT-NIELSEN (1965); 2DANTZLER and SCHMIDT-NIELSEN (1966) ; 3BENTLEY
et at. ( 1967) ; 4RoBERTS and SCHMIDT-NIELSEN (1966); 5BENTLEY (1959b); 6DANTZLER (1967a).
142
ScHMIDT-NIELSEN, 1967a).
The normal rates of urine flow differ considerably in different reptiles (Table 5.4)
and can vary from amounts equivalent to about 0.5% of the body weight in Malaclemys kept in sea-water, to 6% in the gecko lizard and 9% in the caiman when
kept in air. Water loss from the kidney and gut can constitute an avenue of water
loss, which in circumstances when such supplies are restricted, may be physiologically critical. Reptiles, unlike mammals and birds, cannot form a urine that is hyperosmotic to their body fluids and so cannot conserve water by increasing urine concentration in this way. However, some do have the ability to convert increased
amounts of their waste nitrogen into uric acid, which requires less water for its renal
excretion than the alternative products, ammonia and urea. The desert tortoise,
Table 5.4 Variations in the urine {low of reptiles in different states of hydration
mllkg hr
Normal Dehydrated Water loaded Saline loaded
Habitat
Crocodilia
Caiman scleropss
a) In fresh water
b) In air
3.5
1.1
Aquatic
Varies with vasotocin injections
1.3
Aprox.
Anuric
1.0
0.2
2.0
Aprox.
Anuric
0.9 to
Desert
Anuric
2.4
Desert
0.6
Wet
tropical
Anuric
Semidessert
Aquatic
Chelonia
Pseudemys scripta 2
(Slider turtle)
Malacl emys centratas
(Diamondback terrapin)
a) In fresh water
b) In sea-water
Gopherus agassizii»
(Desert tortoise)
Lacertilia
Hemidactylus Sp.4
(Gecko)
Phrynosoma cornutumi
(Horned toad)
Trachysaurus rugosus 5
(Bobtail lizard)
Ophidia
N atrix sipedon':
(Water snake)
2.6
2.0
0.24
1.3
0.8
Anuric
3.6
8.3
12.1
1.8
11.3
0.4 to
Anuric
Aquatic
Estuarine
IBENTLEY and SCHMIDT-NIELSEN (1965); 2DANTZLER and SCHMIDT-NIELSEN (1966) ; 3BENTLEY
et at. ( 1967) ; 4RoBERTS and SCHMIDT-NIELSEN (1966); 5BENTLEY (1959b); 6DANTZLER (1967a).
142