Chameleon - S.S

Chameleons are a highly distinctive and specialised clade of lizards. There are approximatley 160 species of chameleons and they come in a range of colours, the majority of the species also have the ability to change colours. They are found in habitats which ranges from rain forest to desert conditions. The ability of chameleons to carry out colour changes in their skin, helps them in social signalling, camouflage and most importantly in reaction to temperature changes. Colour change signals a chameleon's physiological condition and intentions to other chameleoms. More specifically, the desert-dwelling Namaqua chameleon also uses colour change as an aid to thermoregulation. It changes its colour to black in the morning, when it is colder to absorb heat more efficiently. Then, it changes to a lighter grey colour to reflect light during the heat of the day.

Chameleons are ectothermic, this means they use external (ecto) sources of heat to rasie their body temperature, to its preferred optimum temperature. There are two main ways to do this. There are either Heliothermic animals - they get heat directly from the sun rays. Or there are Thigmothermic animals- they get heat by conduction when touching warm objects. Chameleons are only Heliothermic. Their arboreal lifestyle restricts them to this method, hence to overcome the lack of heating by conduction they have developed both behavioural and physiological methods to make them very efficient Heliotherms. Simply moving into the sunlight (basking) to warm up or into the shade to cool down 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 towards the sun in a way in which they can expose the maximum amount of surface area to the heat source. They also have hinged ribs, which allows them to flatten their body thus increasing the surface area of the side exposed to the heat source. The chameleon will also darken the side exposed to the sun to increase heat absorption, and may lighten the opposite side to retain heat, once absorbed. After changing the shape of its body, and altering its colour the next stage is to change the blood flow rate. The chameleon's heart beats significanlty faster when warming up than when cooling down. This results in the increased heart rate transfer between the warm surface and the cool core. Once the optimum temperature is achieved, the heart rate slows down to reduce heat loss, and the chameleon begins its daily task of hunting for food.