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Abstract

This study investigated the concept of thermoregulatory set-point in
marsupials, by examining behavioural and autonomic thermoregulation in a
laboratory-bred marsupial, the South American grey short-tailed opossum
(Monodelphis domestica) with occasional reference to a single captive sugar
glider (Petaurus breviceps).
Adult animals had clear circadian rhythms of core body temperature
(Tb). Such rhythms were not apparent in juvenile M. domestica and rhythms
in adult animals were disrupted when ambient temperature (Ta) was
reduced, bacterial endotoxin (E. coli LPS) was injected and ambient oxygen
levels were lowered to approximately 10% (i.e. during hypoxia).
Circadian changes in preferred Ta were observed in individual
animals while in a longitudinal thermal gradient but no specific rhythm was
observed. M. domestica was able to make small, but insignificant, changes to
Tb using thermoregulatory behaviour. This resulted in less variance in Tb in
this species while in a thermal gradient.
A typical mammalian fever to LPS and a typical hypothermic
response to hypoxia was observed in M. domestica and one P. breviceps.
Although hypothermic responses to hypoxia have been previously
documented in marsupials, this is the first published account of LPS-induced
fever in marsupials. Preferred Ta was not significantly affected by
hypoxia or fever in M. domestica although a significant reduction in
preferred Ta was observed in the sugar glider while hypoxic. This animal
also selected a warmer environment while febrile. The hypothermic
response to hypo)da in M. domes tica was found to be more significant than
the hyperthermic response to bacterial endotoxin. However, the sugar
glider utilised thermoregulatory behaviour to maintain a hyperthermic
response to bacterial endotoxin even when exposed to hypoxia.
These findings show that in marsupials, as in eutherians,
thermoregulation involves the interaction of autonomic and behavioural
mechanisms. These experiments also highlighted the limitations of using
laboratory bred animals to determine the natural thermoregulatory
capacities of a species.

Item Type:	Thesis - Unspecified
Authors/Creators:	Douglas, Tracy
Keywords:	Opossums, Body temperature
Copyright Holders:	The Author
Copyright Information:	Copyright 2003 the Author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s).
Additional Information:	Thesis (M.Med.Sc.)--University of Tasmania, 2003. Includes bibliographical references
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