Physiological knowledge about most of the 75 genera of Australian marsupials
is lacking, but a modest amount of information is available for some speCies, especially members of the family Macropodidae. The macropods consist of 17 genera
of kangaroos and wallabies, nearly all of which are herbivorous (the diet of musky
rat kangaroos includes worms and insects) and have a grazing manner of life. They
range in size from 500 g in the musky rat kangaroo to 70 kg in the larger members
of the genus Macropus.
MARTIN in 1902 reported that the metabolic rate of several marsupials was
only about one-third as great as would be expected in placentals of comparable
size. That marsupials do indeed have a generally lower basal rate of oxygen
consumption than pla, entals has recently been shown in a variety of species (DAWSON and HULBERT, 1969; ARNOLD and SHIELD, 1970). The basal rate of oxygen
consumption is about one-third less than predicted in a placental of the same size.
This is accompanied by a lower body temperature. It thus seems likely that evaporative water losses from marsupials may be less than in placentals.
Some marsupials have labile body temperatures that change in a characteristic
cycle over the course of each day . This is well shown in the chuditch or western
native cat, Dasyurus geoffroii. The chuditch is a carnivorous marsupial weighing
1 to 2 kg which has a wide geographic range throughout Australia where it even
inhabits the hot desert regions. It is nocturnal in its behaviour coming out to hunt
for food in the evenings. The body temperature of these marsupials changes in a
parallel manner, declining to a minimum in late afternoon and rising as much as
4
0
C in the evening (ARNOLD and SHIELD, 1970). During the period of inactivity
the rate of oxygen consumption was found to be only two-thirds as great as predicted in a placental of the same size. Such changes in the metabolic rate must result
in a conservation of calories and probably also a reduction in the rate of evaporative
water loss. These physiological adjustments could well assist the animals ' survival,
especially in its desert habitats (ARNOLD and SHIELD, 1970).
Information relevant to marsupial osmoregulation is available from three population groups, one living in a temperate and two in desert areas.
Professor HARRY WARING initiated such studies on a small (2 to 5 kg) wallaby,
the quokka, Setonix bracbyurus, that lives in a temperate, but seasonally dry,
habitat on Rottnest island, 18 km from the coast of south west Australia (see Fig.
3.2). Today Setonix is principally confined to this island, though a few isolated pockets of the population remain on the mainland. The annual rainfall on Rottnest is
75cm of which 68 em falls between March and October, so that in the warm summer
months, when the temperature may rise to 38
0
, little rain falls. The vegetation dries
out during this period but isolated soaks of fresh water persist and are frequented
by the quokkas. These animals have been studied in their natural environment and
also in the laboratory where they are quite amenable to physiological investigation.
MARTIN in 1902 reported that marsupials do not regulate their body temperature
adequately in hot environments, an observation that is relevant to their water loss
in such situations. However, it was found that Setonix brachyurus regulated its
body temperature as efficiently as placental mammals at temperatures up to 40 °
(BENTLEY, 1955; BARTHOLOMEW, 1956). This regulation is accompanied by sweating, salivation and panting, and results in a substantial loss of water. When Setonix
is dehydrated, such evaporation of water is reduced by 40% (BENTLEY, 1960) an
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is lacking, but a modest amount of information is available for some speCies, especially members of the family Macropodidae. The macropods consist of 17 genera
of kangaroos and wallabies, nearly all of which are herbivorous (the diet of musky
rat kangaroos includes worms and insects) and have a grazing manner of life. They
range in size from 500 g in the musky rat kangaroo to 70 kg in the larger members
of the genus Macropus.
MARTIN in 1902 reported that the metabolic rate of several marsupials was
only about one-third as great as would be expected in placentals of comparable
size. That marsupials do indeed have a generally lower basal rate of oxygen
consumption than pla, entals has recently been shown in a variety of species (DAWSON and HULBERT, 1969; ARNOLD and SHIELD, 1970). The basal rate of oxygen
consumption is about one-third less than predicted in a placental of the same size.
This is accompanied by a lower body temperature. It thus seems likely that evaporative water losses from marsupials may be less than in placentals.
Some marsupials have labile body temperatures that change in a characteristic
cycle over the course of each day . This is well shown in the chuditch or western
native cat, Dasyurus geoffroii. The chuditch is a carnivorous marsupial weighing
1 to 2 kg which has a wide geographic range throughout Australia where it even
inhabits the hot desert regions. It is nocturnal in its behaviour coming out to hunt
for food in the evenings. The body temperature of these marsupials changes in a
parallel manner, declining to a minimum in late afternoon and rising as much as
4
0
C in the evening (ARNOLD and SHIELD, 1970). During the period of inactivity
the rate of oxygen consumption was found to be only two-thirds as great as predicted in a placental of the same size. Such changes in the metabolic rate must result
in a conservation of calories and probably also a reduction in the rate of evaporative
water loss. These physiological adjustments could well assist the animals ' survival,
especially in its desert habitats (ARNOLD and SHIELD, 1970).
Information relevant to marsupial osmoregulation is available from three population groups, one living in a temperate and two in desert areas.
Professor HARRY WARING initiated such studies on a small (2 to 5 kg) wallaby,
the quokka, Setonix bracbyurus, that lives in a temperate, but seasonally dry,
habitat on Rottnest island, 18 km from the coast of south west Australia (see Fig.
3.2). Today Setonix is principally confined to this island, though a few isolated pockets of the population remain on the mainland. The annual rainfall on Rottnest is
75cm of which 68 em falls between March and October, so that in the warm summer
months, when the temperature may rise to 38
0
, little rain falls. The vegetation dries
out during this period but isolated soaks of fresh water persist and are frequented
by the quokkas. These animals have been studied in their natural environment and
also in the laboratory where they are quite amenable to physiological investigation.
MARTIN in 1902 reported that marsupials do not regulate their body temperature
adequately in hot environments, an observation that is relevant to their water loss
in such situations. However, it was found that Setonix brachyurus regulated its
body temperature as efficiently as placental mammals at temperatures up to 40 °
(BENTLEY, 1955; BARTHOLOMEW, 1956). This regulation is accompanied by sweating, salivation and panting, and results in a substantial loss of water. When Setonix
is dehydrated, such evaporation of water is reduced by 40% (BENTLEY, 1960) an
99