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The physiological mechanisms of endothermy in marsupials : identification of thermogenic abilities and expression of uncoupling proteins

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Kabat, AP (2003) The physiological mechanisms of endothermy in marsupials : identification of thermogenic abilities and expression of uncoupling proteins. PhD thesis, University of Tasmania.

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Abstract

This thesis examines the extent of and the physiological mechanisms behind the
endothermic ability in two marsupials, Bettongia gaimardi and Sarcophilus harrisii. It
also investigates the physiological development of endothermy in the pouch young B.
gaimardi, as well as the expression of uncoupling proteins in several other marsupials
and a monotreme, including Sminthopsis crassicaudata, Trichosurus vulpecula,
Tachyglossus aculeatus, and Perameles gunnii.
This thesis is divided into three main sections. The first section is dedicated to
investigating the thermal mechanisms used by S. harrisii. This chapter identifies the
ability of this species to perform nonshivering thermogenesis by measuring oxygen
consumption prior to and post cold-exposure, and with and without β-agonist
induction. This ability was correlated to the possible expression of uncoupling protein
1 using molecular techniques at both the protein and genetic levels. However, as
uncoupling protein 1 was not identified, the expression of two other uncoupling
proteins was investigated to determine any possible role in thermogenesis. This study
was able to show that S. harrisii expresses uncoupling protein 2 but not uncoupling
protein 3, although this study was unable to shed any new light on the role these
proteins may play. This chapter also reveals that S. harrisii increases intermuscular
temperature in response to long-term cold exposure.
The second section of this thesis deals with the thermoregulatory mechanisms
employed by Bettongia gaimardi. The identification of nonshivering thermogenesis in
the absence of uncoupling protein 1 has been previously documented in the literature,
although the mechanisms behind this ability remain unknown. This chapter
investigates the expression of uncoupling proteins 2 and 3. This study was able to
identify the expression of both proteins in adult B. gaimardi. It was subsequently
determined to use the `ectothermic to endothermic' shift seen in the pouch young B.
gaimardi to identify a possible role for these proteins, as well as identify the
physiologidal developments that occur allowing endothermy to be achieved. These
data established that the pouch young B. gaimardi use a previously undocumented
mechanism of increasing muscle tone in response to the cold. It was also shown that
the pouch young B. gaimardi express uncoupling protein 3 at an early age, and
presumably from birth. However, the pouch young only began to express uncoupling
protein 2 concurrently with the onset of endothermy. This may suggest a role for
uncoupling protein 2 in the development of endothermy. The identification of the novel mechanism of increasing muscular tone in response to
- the cold in the pouch young B. gaimardi prompted a subsequent investigation of this
ability in adults. This was primarily conducted to rule out the possibility that this
mechanism, seen in the pouch young, is not a temporary device only used during the
transition from ectothermy to endothermy. The data, however, suggest that this ability
is maintained throughout the animal's life, although promoted by acclimation to the
cold in the adult B. gaimardi. This may be one possible mechanism of thermogenesis
in the absence of uncoupling protein 1 and/or brown adipose tissue. The final section of this thesis explores the proposal that there is a phylogenetic
difference in the nonshivering thermogenic ability of marsupials and monotremes.
This chapter attempts to correlate the expression of uncoupling proteins 1, 2, and 3
with the reported differences in thermogenic abilities to glean an understanding of a
possible role for these proteins in marsupials and a monotreme. This study looked at
several species of marsupial and one monotreme, that have has their thermogenic
abilities documented, including Bettongia gaimardi, Sarcophilus harrisii, Sminthopsis
crassicaudata, Trichosurus vulpecula, Perameles gunnii, and Tachyglossus aculeatus,
and investigated the expression of uncoupling proteins. It was concluded that no
species used in this investigation expressed uncoupling protein 1, although
uncoupling protein 2 was ubiquitously expressed. There was, however, a phylo genetic
difference in uncoupling protein 3 expression, although there was no positive or
negative correlation with thermogenic ability. This thesis, as a whole, concludes that they may use many of the same
thermoregulatory mechanisms that eutherians use, but may also have evolved some
novel means. It suggests that no marsupials and the echidna use uncoupling protein 1
or BAT in a thermogenic manner, regardless of expression. The expression of
uncoupling protein 3 in marsupials and the echidna is not determined by nonshivering
thermogenic ability, and the protein has no obvious role in thermogenesis. Lastly, this
thesis shows that uncoupling protein 2 is expressed in all species investigated within
this study, and it appears that this ubiquitous protein has a relationship with the
development of endothermy in marsupials.

Item Type: Thesis (PhD)
Keywords: Body temperature, Marsupials
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 (Ph.D.)--University of Tasmania, 2003. Includes bibliographical references

Date Deposited: 19 Dec 2014 02:45
Last Modified: 27 Mar 2017 03:14
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