Color Change in Chameleons
Kimmie McGowen and Madeline Robin
Why Chameleons Change ColorWhile it is commonly believed that chameleons change color in order to camouflage themselves from predators, that is not the only advantage color change provides for the chameleons that express it. Chameleons have also been seen to utilize this skill in a variety of social interactions.
PredatorsChameleons are commonly known to use their color change to camouflage themselves from their predators, specifically birds and snakes. Chameleons will change color to avoid predators either by matching their background to “blend in”, or disrupt their body’s outline. Because chameleons have exceptional vision, they are able to detect predators in the area and camouflage themselves before they are seen.
Species of chameleons that live in trees can produce many shades of green and brown in many different patterns, which allows them to match moss, leaves, twigs, and vines. Species that live in areas of little vegetation have a much more limited ability when it comes to color change. These species are only able to vary their skin’s brightness, so they may appear to be cream, brown, grey, or black, yet they are still successful in camouflaging themselves from predators. Chameleons can also adopt splotchy coloration, which acts as a form of disruptive camouflage. This hinders recognition of the body outline by creating the appearance of false edges and boundaries (Stevens and Merilaita, 2009).
In 2009, Stuart-Fox and Moussalli showed that in 21 populations of dwarf chameleons, 13 populations used different tactics for camouflage depending on whether the predator was a bird or a snake. In all 13 populations that showed responses, the chameleons changed to colors that more closely matched their backgrounds if they encountered a bird, and if they encountered a snake, they would match their backgrounds, but to a lesser degree. With both predators, the chameleons were successful in camouflaging themselves. This is because birds have excellent vision, including a wide range of color perception, whereas snakes have poorer color vision and will be unable to detect chameleons even when their skin doesn’t match the exact hues of their background. This study suggests that chameleons alter their color responses to different types of predators.
Chameleon colour responses to birds are significantly more camouflaged than colour responses to snakes (thin solid line comparisons) in terms of both (a) chromatic (colour) and (b) achromatic (brightness) perceptual channels for both predators. Despite this difference, chameleon responses to snakes are less detectable to the snake visual system than responses to birds are to the bird visual system (a thick dashed line comparison) because snakes have poorer colour discrimination. [From Stuart-Fox, Devi, Adnan Moussalli, and Martin J Whiting. “Predator-Specific Camouflage in Chameleons.”]
Male to Male CommunicationMale chameleons participate in ritualized aggressive displays, which suggests that it is necessary in order to gain access to receptive females and keep other males from doing so. Male chameleons have been observed using species-specific color patterns in aggressive interactions with other males, in addition to physical combat.
Some chameleon species change into display coloration as soon as they see another male. Display coloration during male-male contact varies widely depending on chameleon species. In other species, this color change does not occur until after the males approach each other and elongate their bodies to appear as large as possible. After this, some chameleons may take on “submissive” coloration if their opponent appears larger than they do. Submissive coloration, however, does not vary much by species. All male chameleon submissive colorations are more dark and drab than their displays, usually with the chameleon becoming grey or brown. If neither chameleon take on submissive coloration at this point, the encounter will escalate to physical aggression, involving lunging, biting, and wrestling. This fighting will continue until one of the males changes into submissive coloration and retreats, and the winner maintains his display coloration (Burrage, 1973). These male-male competitions seem to be related to mating success. The winners of contests will show dominant display coloration, which signals to females that they are desirable mates.
Male Coloration by Species
Male and Female CommunicationWhen a male wants to mate with a female, he takes on a vibrant courtship display coloration. This identifies to the female he is displaying for that he is interested in mating.
Females use body color to communicate their interest in mating. If they are unable to mate, females will show conspicuous coloration as a form of courtship rejection. Generally, this is when the female is already carrying eggs, but may also be a signal of non-receptivity. If female chameleons are receptive to mating, they will take on drab coloration to communicate this interest and ability to males (Karsten et al. 2009c).
The conspicuous coloration used to communicate this disinterest by females to courting males varies by species. In the Chamaeleo genus, this coloration is vibrant, dark, or involves highly contrasting coloration (Singh et al. 1983), (Cuadrado 1998b, 2000), (Bustard, 1967), (Kelso and Verrell, 2002). While in the Furcifer genus, females take on a black background with highly contrasting purple, orange, and red spots (in F. labordi) or do not change color at all (F. verrucosus) (Karsten et al. 2009c).
The adaptive value to females of the ability to communicate interest or disinterest to potential mates is generally thought to be because it reduces costs from male courtship and harassment (Cooper and Greenberg, 1992). A potential cost that a female may be able to avoid due to this communication is the time and energy associated with carrying eggs if the female becomes gravid. Female mate choice (where a receptive female may choose to mate with a male or not) is seen in F. labordi. This form of choice corresponds with females mating with more desirable males and passing on mating opportunities with less desirable mates. This allows, over time, the genes responsible for desirable traits to be passed on more frequently to offspring and the undesirable traits to become less common or stop existing altogether.
During copulation, both males and females will take on drab coloration. This allows the chameleons a form of temporary protection against predators while they are mating, which is when chameleons are particularly vulnerable to predators. The drab coloring makes them less visible to some potential threats, such as birds.
Female Coloration by Species