Anolidae are a family of lizards commonly known as anoles (singular anole ) and native to warmer parts of the Americas, ranging from southeastern United States to Paraguay. The family was formerly known as Dactyloidae but it was discovered that the name Anolidae had been used earlier. In the past they were included in the family Polychrotidae together with Polychrus (bush anoles), but the latter genus is not closely related to the true anoles.
Anoles are small to fairly large lizards, typically green or brownish, but their color varies depending on species and many can also change it. In most species at least the male has a dewlap, an often brightly colored flap of skin that extends from the throat and is used in displays. Anoles share several characteristics with geckos, including details of the foot structure (for climbing) and the ability to voluntarily break off the tail (to escape predators), but they are only very distantly related, anoles being part of Iguania.
Anoles are active during the day and feed mostly on small animals such as insects, but some will also take fruits, flowers, and nectar. Almost all species are fiercely territorial. After mating, the female lays an egg (occasionally two); in many species she may do so every few days or weeks. The egg is typically placed on the ground, but in some species it is placed at higher levels.
Anoles are widely studied in fields such as ecology, behavior, and evolution, and some species are commonly kept in captivity as pets. Anoles can function as a biological pest control by eating insects that may harm humans or plants, but represent a serious risk to small native animals and ecosystems if introduced to regions outside their home range.
Distribution and habitat
Anoles are a very diverse and plentiful group of lizards. They are native to tropical and subtropical South America, Central America, Mexico, the offshore East Pacific Cocos, Gorgona and Malpelo Islands, the West Indies and southeastern United States.
A particularly high species richness exists in Cuba (more than 60 species), Hispaniola (more than 55), Mexico (more than 50), Central America, Colombia (more than 75), and Ecuador (at least 40). Fewer live in eastern and central South America (for example, less than 20 species are known from huge Brazil), Contiguous United States (1 native species), and the Lesser Antilles (about 25 species in total, with 1–2 species on each island). However, the Lesser Antilles are relatively rich compared to their very small land area and their species are all highly localized endemics, each only found on one or a few diminutive islands. In South America, the diversity is considerably higher west of the Andes (Tumbes-Chocó-Magdalena region) than east (Amazon basin), as well illustrated in Ecuador where about of the anole species live in the former region and in the latter.
The only species native to the contiguous United States is the Carolina (or green) anole, which ranges as far west as central Texas, and north to Oklahoma, Tennessee and Virginia. Its northern limit is likely related to cold winter temperatures. Several anole species have been introduced to the contiguous US, mostly Florida, but also other Gulf Coast states and California. The most prevalent of these introductions is the brown anole. In contrast to the contiguous United States, Puerto Rico and the Virgin Islands are home to 16 native species, all endemic.
Anoles inhabit a wide range of habitats, from highlands (up to at least above sea level) to the coast, and rainforest to desert scrub. A few live in limestone karst habitats and at least two of these, the Cuban cave anole and Mexican cave anole, will enter caves, sometimes occurring as much as from the entrance. Some species live close to humans and may use fences or walls of building as perches, even inhabiting gardens or trees along roads in large cities like Miami. Most anoles are arboreal or semi-arboreal, but there are also terrestrial and semiaquatic species. They are often, especially in the Caribbean, grouped into six ecomorphs—crown giant, trunk crown, trunk, trunk ground, twig, and grass bush—that inhabit specific niches. Other less widely used groups are ground, ground bush, twig giant, saxicolous, and riparian (alternatively semi-aquatic). However, the species within each ecomorph group are not entirely alike and there are variations in the details of their niches, including both widespread generalists and more restricted specialists. The niche differentiation allows several anoles to inhabit the same locality, with up to 15 species at a single site.
Appearance and behavior
Anoles vary in size. Males generally reach a larger size than females, but in a few species it is the other way around. Adults of most anoles are between in snout-to-vent length, and between in total length, including the tail. In the smallest, the five-striped grass anole, the snout-to-vent length is about in females and males respectively, but it is a relatively long-tailed species. There are several large species that are more than in snout-to-vent length. Males of the largest, the knight anole, reach up to about in snout-to-vent length, in total length, and in weight. There are both robust and gracile species, and the head shape varies from relatively broad to elongate.
The tail of anoles varies, but mostly it is longer than the snout-to-vent length. Depending on exact species it can range from slightly shorter to about three times the snout-to-vent. The Caribbean twig ecomorph anoles, proboscis anole and "Phenacosaurus" anoles have a prehensile tail. Semi-aquatic anoles tend to have relatively tall, vertically flattened tails that aid in swimming, and their skin has certain microstructures that make it hydrophobic, resulting in a thin film of air on the skin surface when submerged and preventing water from staying on when exiting the water.
Underneath an anole's toes are pads that have several to a dozen flaps of skin (adhesive lamellae) going horizontally and covered in microscopic hairlike protrusions (setae) that allow them to cling to many different surfaces, similar to but not quite as efficient as a gecko. Despite this similarity, they are very distantly related and the adaptions are the result of convergent evolution in the two groups. The extent of these structures and clinging ability varies, being more developed in anole species that live high in the tree canopy than ones living at lower levels. In one extreme are anoles that easily can run up windows. In the opposite end of the spectrum is the bulky anole of arid coastal Venezuela and adjacent Colombia, which is the only species completely lacking the specialized toe pad structures. The relative length of the limbs vary, mainly between different species, but to some extent also between different populations of a single species. This depends on things like the preferred perch size and whether there are ground-living predators in a habitat.
Despite having relatively small eyes, their primary sense is sight, which is excellent and in color. Their pupils are round or nearly round. The Guantanamo anole and Cuban cave anole have a transparent "window" in their lower eyelid, allowing them to see even with closed eyes, but why they have this adaption is unclear. Anoles have a good directional hearing, which is able to detect frequencies between 1000 and 7000 Hz and relatively low intensity sounds like the click of a camera.
Anoles are diurnal—active during the daytime—but can also be active during bright moonlit nights and may forage near artificial lights. Many species frequently bask in the sun to increase their temperature, but others are shade-living and do not.
Colors
Most anoles are brownish or green, but there are extensive variations depending on the exact species. The majority can change their color depending on things like emotions (for example, aggression or stress), activity level, levels of light and as a social signal (for example, displaying dominance), but evidence showing that they do it in response to the color of the background (camouflage) is lacking. Whether they do it in response to temperature (thermoregulation) is less clear, with studies supporting it and contradicting it. The extent and variations of this color changing ability differ widely throughout the individual species. For example, the Carolina (or green) anole can change its color from a bright, leafy green to a dull brown color, while the brown anole can only change its shade, ranging from pale gray-brown to very dark brown. Even the distinct green-to-brown change in the Carolina anole can happen in only a few minutes. The colors are the result of their skin pigment cells, the chromatophores, of which they have three main types, but the change occurs only in the melanophores. When triggered by melanophore-stimulating hormone and other hormones, the melanosomes of the melanophores partially cover the other skin pigment cells, giving the anole a darker or browner color. In most cases stress results in a darker/browner color, but in the aquatic anole, a species that is dark brown with a barred pattern and light brown stripes on the sides of its body and head, stress results in paler brown upper parts and the stripes turn pale blue-green.
Their colors during the night when sleeping often differ distinctly from their colors during the day where awake. Among these are some species that otherwise do not drastically change their colors, including certain anoles that generally are brown during the day changing to greenish or whitish when sleeping at night, and certain anoles that generally are green during the day changing to brown when sleeping at night.
Disregarding color change, minor individual variations in the basic color and pattern, mostly related to sex or age, are common. In some anole species this variation is more pronounced and not only related to sex and age. An example of this is the basic color of the Cayman blue-throated anole, which varies geographically, roughly matching the main habitat at a location. In others it occurs at the same location. This includes the extensive individual variations in the Guadeloupean anole, which however also shows some geographic variations, but possibly not consistent enough (due in part to clines) to make the typically recognized subspecies valid. In the Puerto Rican giant anole, a species only able to perform minor color changes (essentially lightness/darkness), juveniles are gray-brown and adults typically green, but an uncommon morph maintains a gray-brown color into adulthood. Similarly, rare morphs of the usually green Carolina anole lack certain pigment cells, giving them a mainly turquoise-blue or yellow color.
Dewlap
Most—but not all—anole species have dewlaps, made of erectile cartilage (modified from the hyoid) and covered in skin, that extend from their throat areas. When not in use and closed it lies inconspicuously along the throat and chest. The size, shape, color and pattern of the dewlap vary extensively depending on species, and often it differs between the sexes, being smaller (in some absent) or less colorful in females. In a few species, including the Carolina, bark, Cochran's gianthead and slender anoles, it varies geographically in color depending on subspecies or morph. Very locally, distinct morphs of a single species that differ in dewlap colors (not just differences between sexes) may occur together. In addition to colors that are visible to humans, dewlaps can have ultraviolet reflectance, which is visible to anoles. The striped anole is the only species where it is asymmetrically colored, being brighter on one side than the other. In some species even juveniles have a dewlap. The West Cuban and Cuban stream anoles are the only where both sexes lack a dewlap, but it is reduced and diminutive in about a dozen other species.