marine reptiles can obtain water by drinking sea-water, but for many species in
a marine situation the propensity to refrain from drinking may be even more vital
to their survival. When an aquatic species, like the caiman, or a terrestrial one like
the box turtle, Terrapene carolina, are placed in sea-water they drink, and as a result
die in a short time (BENTLEY and SCHMIDT-NIELSEN, 1965; BENTLEY et al., 1967a).
The diamondback terrapin and many Pseudemys scripta refrain from drinking such
a bathing medium and can then survive for extended periods. We (BENTLEY et al.,
1967a) onl y observed evidence for drinking (0.2 ml) in a single diamondback terrapin in sea-water, but when such turtles were returned to fresh water after 14 days
in such a fluid, they rapidly imbibed it and excreted the accumulated salt. DUNSON
(1969) has also noted that some marine reptiles, including the banded sea snake,
drink fresh water when it becomes available, while other more fully marine species
like the green turtle, the yellow-bellied sea snake and the Galapagos marine iguana
do not appear to do so. Some accumulation of sea-water through the mouth is probably inevitable by marine reptiles during feeding, but this is probably only minimal.
The ability of a reptile to distinguish between the potability of fresh water and seawater, while appearing a somewhat mundane skill, may be vital to its survival in
adverse osmotic conditions.
Water and salts can be accumulated from the food, some of the water being
in the free form while some will arise as a result of metabolism in the body. The
diets of different species of reptiles is varied and influences their osmoregulation.
Many reptiles , especially many lacertilians, are herbivorous; such fare usually contains plenty of free water and salts, especially potassium. The marine iguana, however, grazes on seaweed which also contains large amounts of sodium and is isoosrnotic with sea-water. Many lizards also eat small invertebrates and an occasional
tetrapod. The Ophidia and Crocodilia are principally carnivorous, a diet from
wh ich they can also obtain sufficient water and salts. Sea snakes appear mainly to
eat fish, a food that has the advantage of being generally hypoosmotic to sea-water
(DUNSON, 1968). Many terrestrial Chelonia are herbivorous or omnivorous while
the marine turtles subsist largely on invertebratess that are isoosmotic with seawater. Such varied diets present different osmotic problems and in many inst ances
may supply adequate or even excess water and salt.
4. Water Metabolism of the 'Dob'
GRENOT (1967; 1968) has given a very interesting account of the life, habits and
osmoregulation of a lizard that lives under the extremely dry conditions of the Sahara desert. This agamid, Uromastyx acanthinurus, is locally called the 'Dob' or
'Fouette-Queue' (whip tail). The aridity of the Sahara is legendary, and in the area
of Beni-Abbes, where these lizards were studied, the daily air temperature can rise
to 47
0 while that on the earth's surface may be 70
0
• Rainfall is uncertain and is
as little as 0.3 mm in a year. The 'Dob' lives among outcrops of rocks, on which,
by either basking in the sunshine or seeking the cool refuge of crevices and cracks,
it can regulate its body temperature and at the same time reduce evaporative water
loss. The importance of such behaviour was shown by the high mortality rate of
lizards tethered in the sun without shelter. When these lizards were kept without
158
a marine situation the propensity to refrain from drinking may be even more vital
to their survival. When an aquatic species, like the caiman, or a terrestrial one like
the box turtle, Terrapene carolina, are placed in sea-water they drink, and as a result
die in a short time (BENTLEY and SCHMIDT-NIELSEN, 1965; BENTLEY et al., 1967a).
The diamondback terrapin and many Pseudemys scripta refrain from drinking such
a bathing medium and can then survive for extended periods. We (BENTLEY et al.,
1967a) onl y observed evidence for drinking (0.2 ml) in a single diamondback terrapin in sea-water, but when such turtles were returned to fresh water after 14 days
in such a fluid, they rapidly imbibed it and excreted the accumulated salt. DUNSON
(1969) has also noted that some marine reptiles, including the banded sea snake,
drink fresh water when it becomes available, while other more fully marine species
like the green turtle, the yellow-bellied sea snake and the Galapagos marine iguana
do not appear to do so. Some accumulation of sea-water through the mouth is probably inevitable by marine reptiles during feeding, but this is probably only minimal.
The ability of a reptile to distinguish between the potability of fresh water and seawater, while appearing a somewhat mundane skill, may be vital to its survival in
adverse osmotic conditions.
Water and salts can be accumulated from the food, some of the water being
in the free form while some will arise as a result of metabolism in the body. The
diets of different species of reptiles is varied and influences their osmoregulation.
Many reptiles , especially many lacertilians, are herbivorous; such fare usually contains plenty of free water and salts, especially potassium. The marine iguana, however, grazes on seaweed which also contains large amounts of sodium and is isoosrnotic with sea-water. Many lizards also eat small invertebrates and an occasional
tetrapod. The Ophidia and Crocodilia are principally carnivorous, a diet from
wh ich they can also obtain sufficient water and salts. Sea snakes appear mainly to
eat fish, a food that has the advantage of being generally hypoosmotic to sea-water
(DUNSON, 1968). Many terrestrial Chelonia are herbivorous or omnivorous while
the marine turtles subsist largely on invertebratess that are isoosmotic with seawater. Such varied diets present different osmotic problems and in many inst ances
may supply adequate or even excess water and salt.
4. Water Metabolism of the 'Dob'
GRENOT (1967; 1968) has given a very interesting account of the life, habits and
osmoregulation of a lizard that lives under the extremely dry conditions of the Sahara desert. This agamid, Uromastyx acanthinurus, is locally called the 'Dob' or
'Fouette-Queue' (whip tail). The aridity of the Sahara is legendary, and in the area
of Beni-Abbes, where these lizards were studied, the daily air temperature can rise
to 47
0 while that on the earth's surface may be 70
0
• Rainfall is uncertain and is
as little as 0.3 mm in a year. The 'Dob' lives among outcrops of rocks, on which,
by either basking in the sunshine or seeking the cool refuge of crevices and cracks,
it can regulate its body temperature and at the same time reduce evaporative water
loss. The importance of such behaviour was shown by the high mortality rate of
lizards tethered in the sun without shelter. When these lizards were kept without
158