Evolution of the Colour Changing Ability in Chameleons Essay Example
In today’s world, there are a variety of organisms that have evolved the ability to change colours in response to environmental stimuli. Within the Chamaeleonidae family, there are about 150 species of chameleons that may change colour due to brightness shifts or chromatic colour changes (X). Iridophore, which are made up of guanine crystals, are made up of guanine crystals, are a particular layer of cells in their bodies. These crystals change structures and move when chameleons relax and excite their skin, allowing the reflection of different wavelengths, producing the colour changes observed (X).
The evolution of colour change in these chameleons has been a conflicting debate, between natural selection to avoid predators or sexual selection to find a mate. Despite the misconception that colour change evolved for the purpose of camouflage, recent studies indicate a stronger selection for social signalling interactions and thermoregulation (X).
The social signalling hypothesis explains one factor towards the evolution of colour change in chameleons. Social signalling is a form of communication for animals to attract mates or intimidate rivals. The hypothesis predicted a positive relationship between colour change and signal conspicuousness in African dwarf chameleons (X). Chameleons demonstrate the greatest capacity for chromatic colour change when their display signals are highly conspicuous to conspecifics (X). These large colour changes occur in social interactions, when chameleons are expressing dominance signals, such as aggressive interactions and the courtship of females (X). This is in contrast with the function of crypsis, as chameleons do not show an increase in colour change capacity in response to its background (X).
Chameleons will undergo a chromatic colour change to indicate their desire to mate. When in proximity to a reproductive female, chameleons will ignore the background colour, risking crypsis and exposure to predators (X). They will thus prioritize being distinctive to the females and engage in social signalling. A chameleon in a relaxed state will remain in its natural state of green or brown to camouflage with its surroundings. In contrast to the excited state, where they will shift to brighter colours to stand out or defend against competing males (X). They can shift the background colour of its skin by increasing the distance between the guanine nanocrystals in the S-iridophores, to reflect longer wavelengths of light, producing a yellow and orange hue. (Fig.1; X).
In the absence of the larger dominating male, small and subordinate male chameleons will use sneaking tactics to court females (X). In the presence of a female, chameleons who utilize this mating strategy are more likely to switch to courting colours than huge dominating males (Fig.2; X). To obtain an opportunity with the female before a dominant male or predator approaches, the subordinate males shift to courting colours quicker and more frequently (X). Subordinate chameleons benefit from this since they are not systematically excluded from courtship and reproduction.
Chameleons use their colour changing abilities to reflect aggressive behaviours towards male-to-male competition (X). These animals exhibit a chromatic shift to darker shades, for instance from green to red, in order to assert dominance over their competitors (X). Male chameleons with greater stripe brightness are more likely to approach another male in an antagonistic manner. A brighter head colouration and a quicker colour change are indicators that they are more likely to win these aggressive encounters (X). By signalling to their competitors, chameleons can assess the situation and ensure that the aggressive encounters are less costly. Smaller chameleons are able to avoid conflicts in instances where they would lose, and larger chameleons are able to conserve time and energy for stronger opponents. During competitions, these signalling mechanisms allow chameleons to transmit motivation or ability, which may contribute to evolutionarily stable tactics (X).
The ability to colour change also has an impact on the thermoregulation of chameleons. They are able to moderate the ability to change colours based on their habitat’s conditions and the air temperature (X). When the temperature of the air changes, the distance between the guanine crystals changes, causing the S-iridophores' reflectance to fluctuate between short and long wavelengths (X). The change in reflectivity results in various shifts in chromatic colour displays to allow for maximal and minimal sunlight absorption. A dense layer of D-iridophores sits beneath the S-iridophores, reflecting a considerable percentage of the sun's energy and reducing excess solar absorption (X).
Chameleons move to regions where their bodies are oriented towards the rays of the sun, in combination with darker body colours that result in maximum heat absorption (X). When preferred thermal levels are achieved, chameleons switch to lighter body colours to decrease heat absorption and reflect the rays of the sun. Overall body temperatures are stabilized as a result of this movement and colour shift (X). This feature aids in the chameleons survival by allowing them to adapt to their surroundings, demonstrating a selection pressure for colour change evolution.
Overall, the evolution of the colour changing ability in chameleons was not for the main purpose of blending in and obtaining crypsis, but rather to stand out. Although colour change may have originally evolved for crypsis, the following evolution of chromatic colour change has provided chameleons with a strategy to facilitate social signalling as a means of communication (X).
