This article provides a general introduction to the taxonomy, distribution, and characteristics of chameleons in general, before moving on to review current knowledge of the natural history of the Panther chameleon Furcifer pardalis.
Chameleon Taxonomy and Distribution
Chameleons are medium sized Old World lizards from the family Chamaeleonidae. Around 180 species and subspecies of chameleons have been described from countries in tropical and sub tropical regions. The majority of chameleon species are native to sub-Saharan Africa and Madagascar, although chameleons are also found on the Indian Ocean islands making up the Seychelles and the Comoros, northern Africa, southern Europe, the Middle East, southern India and Sri Lanka. Chameleons have also been introduced by humans to Crete, Greece, the Canary Islands, Reunion Island, Mauritius, the Hawaii, and isolated pockets of California and Florida in the USA where they now live as feral populations.
While the exact site of origin of chameleons remains a controversial topic, it is widely thought that they probably originated on the Island of Madagascar around 45-90 million years ago. Since there origin it is likely that chameleons have undergone several dispersal events from Madagascar to Africa, the Comoros islands, the Seychelles, and possibly the island of Reunion. These dispersal events are likely to have facilitated by floating logs and tree rafts carried by ocean currents. The relocated colonists then diverged in to new chameleon species.
There are two subfamilies of chameleons (family Chameleonidae). The first subfamily is called the Chameleoninae, and consists of the larger arboreal (tree dwelling) species of the genera Chamaeleo (Africa and Asia), Bradypodion (South Africa), Calumma (Madagascar), Furcifer (Madagascar) Kinyongia (Africa), and Nadzikambia (Africa). The second subfamily is called the Brookesinae, and consists of the smaller ground dwelling dwarf chameleon species of the genera Brookesia (Madagascar), Rieppeleon (Africa) and Rhampholeon (Africa). Approximately 40% of chameleon species (both arboreal and dwarf species) are native to the island of Madagascar, a large island in the Indian Ocean off the east coast of southern Africa. Indeed, the chameleons are one of the faunal groups that continue to make Madagascar a paradise for naturalists. All chameleon species native to Madagascar are egg layers, while some species found on mainland Africa give birth to live young.
Chameleon Anatomy and Physiology
Chameleons are diurnal (active during the day) poikilotherms (organisms with an internal body temperature than varies considerably). Chameleons require solar radiation to keep their bodies at optimal temperature, and fairly high relative humidity levels.
Chameleons have a number of distinctive anatomical features. These include:
Turreted, independently moving eyes: Chameleons have the ability to rotate their eyes by 180 degrees in almost every direction, independently of one another. This gives them a 360 degree arc of vision around their bodies, allowing them an unobstructed view of the surrounding environment in all directions and without the need to move their head or body. Each eye can focus independently, allowing chameleons to view two objects simultaneously in different directions. Chameleon eyes offer a narrow field of vision through a small opening in the eyelids just big enough for the pupil to see through. Chameleons rely on their stereoscopic vision to accurately judge distances for catching insect prey. When prey is located, both eyes are focused on it giving an incredibly accurate “aim”.
Parietal eye: The parietal eye is a light sensitive vestigial eye covered in scales.
Projectile tongue: Chameleons capture insect prey by firing out their long tongues. The long muscular tongue is an evolutionary adaptation that enables arboreal feeding. Chameleon’s tongues can be extremely long, longer even than the length of the animals body. The tongue is made up of bone, muscle and sinew. At the base of the tongue is a rod made of bone that is shot forward, giving the tongue rapid momentum. The tip of the tongue features an enlarged muscle, glands that secrete a sticky saliva, and microscopic hooks and rings. These structures form a kind of suction cup that very effectively sticks to prey. the tongue commonly hits the prey item about 30 thousandths of a second after being fired. As soon as the tongue makes contact with an insect it is immediately retracted back in to the mouth. The eyes close for protection as the tongue is retracted, and the prey is crushed by the chameleons jaws before being swallowed.
Internal ear: Chameleons ears are not visible from the outside as they are covered in skin and scales. They can only hear a narrow range of sound vibrations (200Hz to 600Hz).
Prehensile tail: Chameleons use their outstretched tails to balance while walking, and as a fifth limb when climbing (in arboreal tree dwelling species). At night the tail is curled up while the animal sleeps. Unlike other reptiles chameleons don’t have the ability to regenerate their tails.
Grasping feet: Chameleons have zygodactyl grasping feet with opposable toes that look and work like tongs. Chameleons front feet are made up of two fused toes on the outside of the foot and three fused toes on the inside of the foot. The reverse is true for the back feet, with three fused toes on the outside of the back foot and two fused toes on the inside of the back foot. The feet are also equipped with claws and pads to ensure a firm grip on bark and branches, enabling the animal to feed successfully as well as retreat from predators.
Color changing skin: The primary function of a chameleons scaly skin is to protect the internal organs and maintain correct internal body chemistry and temperature (homeostasis). Being ectothermic, chameleons absorb heat from the sun. On cool mornings chameleons often display darker coloration in order to better absorb infared heat from the sun.
The skin is also used in camouflage and communication. Chameleons are known for their striking colors and patterns, as well as their ability to rapidly change color. Chameleons have evolved highly specialized pigmented skin cells called chromatophores that facilitate color change. It is a commonly held belief that chameleons change color to blend in to their surroundings, and have been called the masters of camouflage. Indeed, chameleons do employ cryptic coloration, body shape, and locomotion (by either staying still or moving in a way that resembles leaves blowing in the wind) in order to avoid predation by birds and to hunt insect prey. The color of an individual chameleon is highly dependent upon its genetics, gender, age, emotional state, physical health, temperature and light intensity. The most dramatic rapid color changes are often due to a change in emotional state, which can be triggered by a number of stimuli, especially the presence of other chameleons of the same species. Individual chameleons use dramatic color changes and body positioning to communicate with one another. For example, males use flashy colors to court females, as well as to scare off other males. Males often display to one another during the breeding season. If neither male submits (by darkening its coloration and leaving the area), an escalating battle often ensues, complete with dramatic coloration, hissing, headbutting, and biting. Chameleons shed their skins as they grow, exfoliating old skin in multiple patches and flakes. Shedding occurs more frequently in juveniles when growth is more rapid.
Panther Chameleon (Furcifer pardalis) Distribution, Habitat, and Environment
The Panther Chameleon (Furcifer pardalis) is a relatively large (males over 50cm, females up to 30cm in length), colorful species of chameleon. Like most chameleon species, Panther chameleons show sexual dimorphism (differences between males and females). The feet of Panther chameleons are relatively small for a large species of chameleon, and their grip is not particularly strong.
The Panther chameleon inhabits the low elevation warm humid zone in the northwest, far north, and northeast (about one third of the way down the island) of Madagascar. The average daily temperature in its habitat ranges from a moderate 23°C (73.4°F) in winter, to a hot 28°C (82.4°F) in summer. To the east, the climate is wet year round, while the north and northwest is characterized by distinct summer-wet, winter-dry seasons. The original habitat was comprised of tropical rainforest in the east, and a mosaic of seasonally dry forest and savannah in the north west. It must be stated however that much of the original vegetation making up these habitats has been degraded by human activity over the past 2000 years.
It is possible the Panther chameleon has benefited from the habitat degradation that has occurred across its range. Indeed, Panther chameleons seem to thrive in degraded habitat, and are commonly found living along roadsides and next to human dwellings. This suggests that they are primarily a forest edge species, although it is possible that they also inhabit the forest crown of mature forests.
Behavior and Demography of the Panther Chameleon
The social structure of Panther chameleons (and indeed most chameleon species) is poorly understood at present. The commonly held paradigm is that Panther chameleons are solitary and territorial (both males and females of all ages), although males and females are often found close together in pairs during the breeding season. Adult male Panther chameleons are particularly aggressive and intolerant towards other males during the breeding season. Should two adult males come in to view of each other in one of the males territory (shrub or tree) during the breeding season they will start to display to one another. These displays consist of an intensification of color, body and gular pouch inflation, gaping, coiling of the tail, standing tall, and rocking side to side. In some cases the intruder will back down. Should the intruder remain within the other males territory, it will be perused and attacked. These fights often result in serious injuries, which is why male Panther chameleons are kept alone in captivity.
Male Panther chameleons also display to nearby females during the breeding season. Displays consist of intensification of colors, rocking head motions, and emitting purr like vibrations. Females remain passive when receptive to the advances of males. At times when females are not receptive to males they will communicate the fact visually by gaping, rocking, and using body coloration. It is thought that during the breeding season, male Panther chameleons guard and defend females in breeding condition for short periods of time, during which they mate. Once the females become unreceptive, them males move on, looking for another female to repeat the process with. This process is known as serial polygyny. The copulation process involves the male seizing the females tail, then the flanks in order to get into position. When mounted and in position, males align their cloaca with that of the female. He will then insert his hemipenis inside the females cloaca. The male then withdraws and the female quickly moves away. Females usually oviposit (lay eggs) 3 to 8 weeks after copulating. Females descend to the ground and excavate a burrow at least 15cm deep, laying the eggs in a round chamber at the end of the burrow. After laying the eggs, females fill in the burrow and cover the entrance, making it visually inconspicuous.
During the breeding season, one or more clutches of eggs are laid. There seems the be a great deal of variation in clutch and egg size, although egg size/mass within a clutch are fairly similar (with the exception of the occasional few eggs being smaller or larger than the rest). Clutch sizes range from 12 to 46 eggs. In captivity the egg incubation period varies considerably from about 160 to 330 days, although studies conducted on Reunion island suggests an average incubation period of 360 days, with eggs hatching in late spring/early summer rainy season when insect life is abundant. Eggs are thought to undergo a diapause period (when temperatures are high) during which time embryo development slows down until an environmental trigger (low winter temperatures followed by elevated temperature) ends the diapause and accelerates development. A consequence of this diapause is that hatchlings from successive clutches hatch simultaneously in the late spring or early summer rainy season when condition are favorable. It should be noted that areas with less well defined seasons are likely to have less well defined hatching periods as a result.
Information on the demographics of panther chameleon populations is fairly patchy, and is mainly based on inference and casual observation rather than rigorous scientific study. It is thought that 20% of eggs laid during the summer and early fall (January to May) will hatch. The majority of eggs will hatch in late spring or summer (December to February). Newly hatched baby chameleons grow rapidly, reaching sexual maturity in around 6 months. Little is known about mortality rates among wild Panther chameleons but it is thought that egg predation by ants could be significant. The Madagascar hognosed snake Leioheterodon madagascarensis also preys extensively on lizard eggs, including those of chameleons. Young Panther chameleons are eaten by adult chameleons, while chameleons of all ages are eaten by birds of prey, snakes, and seem to suffer especially high mortality during the winter. Panther chameleons reach sexual maturity after 7 months (minimum) or more. Some surviving juveniles therefore become mature adults in the fall of the same year as they hatch, and some even breed in their first year. The majority however (males especially) delay breeding until the following summer.
Overall, studies suggest high mortality rates of Panther chameleons of all ages in the wild. Mortality rates are thought to be especially high during and immediately following the breeding season due to predation, endoparasitic infestation, and the high energy expenditure involved in fighting (males) and egg laying (females). Decreasing temperature, relative humidity, and availability of insect food are also thought to contribute to mortality rates at this time. The result of these factors is that few individuals survive their second winter in the wild.