Thermoregulation


How a chameleon thermoregulates


 

Chameleons are Ectothermic.
This means they use external (ecto) sources of heat to raise their body temperature to its Preferred Optimum Temperature (P.O.T.).

There are two main ways to do this.

A Heliothermic (sun loving) animal gets its heat directly from the suns rays.


A Thigmothermic animal gets its heat by conduction when touching (thigmo) warm objects. E.g. hot basking rock.


Most reptiles at some stage use both methods. Clearly if basking on a rock in full sun the animal will be exposed to conducted heat and direct sun light. This is a very efficient way of warming up quickly.


Chameleons however are only Heliothermic. Their arboreal lifestyle restricts them to this method. To overcome the lack of heating by conduction they have developed both behavioral and physiological methods to make them very efficient Heliotherms.

Simply moving into the sunlight (basking) to warm up and into the shade to cool down or maintain body temperature is the most basic form of temperature control. Chameleons take this principle several stages further.

Firstly they bask Laterally. This means they position their body to be side on to the sun thus exposing the maximum amount of surface area to the heat source.

Pic of cham by basking bulb side on


Chameleons also have hinged ribs.
This allows them to flatten their body thus increasing the surface area of the side exposed to the heat source.

Pic here of cham flattening ribs


In addition the chameleon will darken the side exposed to the heat source to increase heat absorption and may lighten the opposite side to retain heat once absorbed.

Pic of cham in dark colours ie basking first thing

This lightening of the side in shade also acts as camouflage as any predator looking from below the chameleon would find the lighter side harder to see with the light behind it. This "light underside" principle is the same as most frogs and birds use.

After changing the shape of its body and altering its colour the next stage is to alter the blood flow rate. The Chameleons heart beats significantly faster when warming up than when cooling down. This results in the increased heat transfer between the warm surface and the cool core.


Once the P.O.T. is achieved the heart rate slows down to reduce heat loss and the chameleon begins the daily task of hunting for food.


Reaching the P.O.T. positively and directly influences the Chameleons ability to hunt, capture and digest prey.
A Chameleon at its P.O.T. moves quicker, is more accurate with its tongue and has faster and more efficient digestion than one that is below the P.O.T.

 

 


Thermoregulation in unwell Chameleons


Chameleons like many other reptiles thermo-regulate differently when ill.
An ill Chameleon will increase it's basking thus raising its body temperature to above the usual P.O.T. They are effectively giving themselves a fever, which aids the efficiency of their immune system.

In very serious or more advanced cases of illness a sick Chameleons will often seek out the coldest darkest area of the enclosure and stay there Often refusing to more regardless of stimuli or enticement offered.
It is believed that the stress from the illness plus any previously suppressed stress (could be environmental or social or both) acts to suppress the immune system. To allow the immune system to gain control again the chameleon must shut down as many of its systems as possible to protect its self from further harm.

It should be noted that this is absolutely not a recommended method of treating a sick animal but rather the animals final attempt to gain control of an illness which is already at an almost fatal level.

 


Creating a basking spot



Changing the wattage of a bulb used to create a basking spot directly effects the light and heat at the basking spot.
When creating a basking spot the aim is to create a bright area as well as a hot area as reptiles associate bright light with heat. If a dimmer stat is used with for example, a 100w bulb the bulb may only be burning very slightly for the area beneath it to reach the required temperature and consequently would produce very little light. It would also gradually warm up the rest of the enclosure resulting in a reduction of the thermal gradient therefore effecting the animals ability to thermo-regulate properly.
A better option would be to use a lower wattage bulb that needs burn brightly all the time to achieve the required temperature which consequently would also create the desired bright spot as well.
Often the wattage of the basking bulb needs to be changed throughout the year. A small wattage bulb is usually used during the summer where there is naturally a higher ambient temperature and a higher wattage bulb for the winter.

A thermostat should be used in all cases to control the maximum temperature at the basking spot, particularly as Montane species have a tendency to cook themselves if basking spot too warm.

Remembering chameleons are lateral baskers, the spot light should be angled.


Thermogradient


 

A typical chameleon set up is shown below. The diagram shows how a bulb can be used to create a thermal (heat) gradient.

Notice the UV source is very close to the basking bulb so when the chameleon basks to warm up it will receive the highest level of UV as it would do naturally when basking in the sun.



A - This area is too hot for the animal to enter.
Perches/plants should be kept away to avoid
the risk of thermal burns to the animal.

B - This area is termed the "basking area" and
represents the maximum safe temperature
where the animal can quickly heat up
until its body achieves the desired temperature.
This maximum temperature is species specific.

C/D- The animal will spend most of its time in
these areas once its body is warm enough.

E - This area is effectively unheated and should
always be sufficiently cool for the animal to be
able to retreat to on hot days. Ideally there
should be around a 20 degree difference
between areas B and E.

1 - Perch 1 allows basking and high UV exposure.
The left of the perch allows the animal to cool
off slightly but still allows high UV exposure.
2 - From right to left on Perch 2 both temperature
and UV exposure reduces.
3 - Perch 3 allows the animal to cool down when
the ambient temperature is too hot but will not
offer any UV exposure.

 

In the above example a normal household pearl spot bulb was used. We find a normal tungsten bulb adds parts of the spectrum that UVB Flourescent bulbs do not produce therefore giving a more natural light.

Note: Area E can only be the same temperature as the surrounding ambient temperature. This will go up and down according to the temperature of the room it's in. If it measures 70°F during the winter and the temperature in the room goes up to 90°F iin the summer the coolest spot is also going to be 90°F.

This might sound obvious but we get e-mails all the time quoting cold temperatures which have only been measured once. They are amazed when they measure it again and find the don't have a cool area anymore. Unless your room is air conditioned its going to vary. Don't guess, always use a thermometer and measure constantly as well as maximum and minimum temperatures.

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