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Thermoregulation in Australian animals

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Luke Parsons

on 13 May 2014

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Transcript of Thermoregulation in Australian animals

Thermoregulation in Australian animals:
The koala has a coating of fur which helps to maintain a steady temperature by insulating the koala's skin. This fur is the most insulating of any marsupial. In hotter regions, this fur is thinner, while in cooler regions the fur is thicker and longer, helping to retain more heat.
Size and shape
Koalas only grow to a relatively small size of 60-85 cm as an adult. This size, combined with their round shape, allows the tree-dwelling koala to expend less energy by having a larger surface-area to volume ratio. Koalas from Victoria are twice as large as those from Queensland.
Toxin resistance
The oils in the leaves of the eucalyptus tree are highly toxic to most creatures, but koala livers have evolved a resistance to the toxin, enabling them to rely on the high water content of the leaves for the koala's water needs and by extension, its thermoregulatory needs.
Metabolic rate
The koala has an extremely slow metabolic rate, about half of other animals. This allows koalas to survive on nutrient-poor eucalyptus leaves and also produce far less heat, allowing for easier thermoregulation.
Small brain
The koala has one of the smallest brains in proportion to its body of any mammal - 60% smaller than normal. As the brain is generally the main source of heat, this adaptation helps reduce the heat the koala produces significantly, and also reduces its energy requirements.
Koalas have a very low-energy diet. This leads them to require 20 hours of sleep a day, and they only engage in about 4 minutes of active movement per day. Most of this activity takes place at night when weather is cooler, further helping to reduce heat production and assist in thermoregulation.

Koalas are almost always up in the trees where they can eat easily, and keep away from the hot ground. When it's hot, the koala dangles its arms from the branches to increase surface area for heat loss; when it's cold or wet, the koala curls into a ball to retain more heat.
The Frill-Necked Lizard (Chlamydosaurus kingii)
(Phascolarctos cinereus)
of the koala
of the koala
of the koala
Wind avoidance
Koalas avoid the heat-stealing wind of the Australian plains by changing their altitude in the trees. When there's more wind, they move down lower where there's more protection from the wind.
of the Frill-necked Lizard
The Frill
The Frill-necked Lizard gets its name from the large flap of skin that lies against its neck and can be raised up when needed. Among many other purposes, the angle of the frill can be adjusted to catch more or less sunlight when the lizard basks.
of the Frill-necked Lizard
Frill blood supply
It is thought that the Frill-neck Lizard can control the amount of blood flowing through its frill in order to thermoregulate. The extremely thin skin of the frill allows blood to heat or cool quickly, depending on the weather.
Body clearance
To help grip onto the trees where it lives, the frill-necked lizard has long limbs and claws. This feature also helps thermoregulation by keeping more space between the lizard's body and the often very-hot ground while the lizard is running from tree to tree.
of the Frill-necked Lizard
Much like other ectotherms, the Frill-neck's primary source of heat is the sun. Each morning, its period of activity begins when the ambient temperature starts rising. The lizard will lie on hot rocks or on sunlit branches until its body temperature is high enough. Then throughout the day, it will control its temperature by avoiding or absorbing heat from the sun.
While the Frill-necked lizard generally moves around on four legs, it can also run on two legs when it needs to. This behaviour appears when evading a threat, and also acts as a way to avoid overheating. The Australian outback's ground is very reflective of heat, so by running on two legs instead of four, the lizard reduces the heating it receives.
body temp
medulla oblongata
medulla oblongata
blood pressure increase,
more blood in frill;
temp increases
body temp up
medulla oblongata
medulla oblongata
blood pressure decrease,
less blood in frill;
less heat
Lizard Thermoregulation loop
When koalas are hot, they pant, utilising evaporative cooling from the inside of their lungs, in order to cool down.
"Frilled Lizard." Burke's Backyard Fact Sheets. N.p., n.d. Web. 9 May 2014. <http://www.burkesbackyard.com.au/factsheets/Conservation-and-the-Environment/Frilled-Lizard/1155>.
"Frilled Lizards." National Geographic. N.p., n.d. Web. 4 May 2014. <http://animals.nationalgeographic.com.au/animals/reptiles/frilled-lizard/>.
"Frilled Neck Lizard - Chlamydosaurus Kingii." Australian Reptile Park. N.p., n.d. Web. 5 May 2014. <http://www.reptilepark.com.au/animalprofile.asp?id=84>.
"Frilled Neck Lizard." Frilled Neck Lizard. N.p., n.d. Web. 6 May 2014. <http://www.australianfauna.com/frillednecklizard.php>.
"Frilled-neck Lizard." Wikipedia. Wikimedia Foundation, n.d. Web. 8 May 2014. <http://en.wikipedia.org/wiki/Frill-necked_lizard#Thermoregulation>.
"Koala Morphology." Davidson Biology. N.p., n.d. Web. 8 May 2014. <http://www.bio.davidson.edu/Courses/anphys/2000/CrawfordC/morphology.htm>.
"Metabolism and Heat Balance in an Arboreal Marsupial, the Koala (Phascolarctos Cinereus) - Springer." Metabolism and Heat Balance in the Koala. N.p., 12 May 1979. Web. 2 May 2014. <http://link.springer.com/article/10.1007%252FBF00709996#page-1>.
Both the koala and the frill-necked lizard are primarily arboreal, but their methods of thermoregulation are vastly different, due to one being an ectotherm and the other an endotherm. Koalas rely on positioning within their tree; their natural shape and fur coating; and their slow metabolic rate. The frill-necked lizard, on the other hand, relies on active blood redirection, basking, carefully timed bursts of activity, and its frill. They are both uniquely and highly adapted to the Australian environment.
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