-- by Thomas A. Jenssen, Biology Department, Virginia Tech
If you live in the southeastern United States, you might be lucky enough to have the green anole (Anolis carolinensis) sharing the yard and garden with you. This small and rather unassuming lizard can be found basking or scurrying about in its normal bush and tree habitat, but it can also adjust to using decks, walls, and other human-made structures as part of its home range. The green anole is so named because it is usually bright green, though it can shift to brown when it is cold or socially stressed. The green anole is particularly noticeable during the breeding season (April-July), when territorial males frequently move about on patrol and advertise their domain with visual displays. These displays, consisting of head bobbing and the extension of an impressive pink throat fan (also called a dewlap), make the males quite conspicuous. You might note these little lizards with a passing curiosity, but really not give them much more thought. However, the green anole deserves a much closer look because it has a very interesting social system.
Anolis carolinensis is a member of the largest genus of lizards, totaling more than 375 species. Almost all of these anoline species are found in the tropics. However, the green anole is one of the exceptions, being distributed as far north as southern Virginia and Tennessee, and eastward to central Texas and southeastern Oklahoma. The species is quite versatile and does well in most any subtropical climate. It even has a stronghold in Hawaii, where it was introduced in about 1950.
Male dewlap display
The green anole is sexually dimorphic; that is males and females may have different expressions of a trait. A couple of obvious sexually dimorphic traits are the large body and dewlap sizes of males. Body length, as measured from the tip of the nose to the end of the trunk (i.e., snout-vent-length), is about 15 % greater for males than for females. This is usually the case in species where males fight for multiple females (i.e., polygyny). In A. carolinensis, the bigger the male, the more females he is able to guard (up to six females). The male's dewlap is three times the area of the female's dewlap, and appears to be an important indicator to other males as to just how big a displaying male actually is. By displaying, big males attempt to keep smaller males away from guarded females. Male territories will average about 70 m3 in habitat volume in which females will be relatively clustered in small, overlapping home ranges of about 8 m3 of habitat. Besides averaging more than 100 displays/hour, these males will move about 27 m/hour patrolling the perimeter of the females’ home ranges to keep other males away. This kind of mating system has been labeled “female-defense polygyny”.
Male (left) and female (right) anoles
Unlike most lizards that lay one large clutch of eggs per year, anoline lizards lay a series of single-egg clutches. An A. carolinensis female will lay an egg about every week during the 4-month breeding season. This means that a female may lay a total of 15-18 eggs for the summer. For each weekly clutch, a female first becomes sexually receptive, and will move to where the resident male can see her. The female signals that she is receptive by bending her neck when a male approaches, so that he might take a neck hold. During these encounters, which are fairly brief (1-2 minutes), the male will decide whether he wants to copulate. About 70% of the time he does not take a neck hold, and will move off. When copulation does occur, the male and female will be occupied for 30-60 minutes. Females can store sperm, and should the territorial male disappear and no new male replace him, a female can continue to lay fertile eggs for the rest of the breeding season. When laying an egg, a female will first dig a shallow hollow in the soil or mulch, usually on the ground, but occasionally above ground (e. g., in accumulated organic matter in the axil of a tree limb). She then backs into the depression, lays the egg, and covers the egg with surrounding material. No more parental care is given, and upon hatching 6-8 weeks later, the little neonate is on its own.
Males expend much energy in territorial defense that includes patrol, aggressive signaling to neighboring males, and occasional chases or actual fights with intruders. Males lose body weight over the course of the breeding season as they defend their harems. Many males are displaced by other males when exhaustion sets in. One study found a 75% turnover rate on defending males during the 4-month breeding season. Breeding females, on the other hand, can be very inconspicuous. They only display occasionally, and then it is when approached by a male or during the rare (about once/ 8 hours) aggressive encounter with a female neighbor. Females also limit their movements to about a fifth that of males. However, after the breeding season, males and females act much alike because males stop patrolling and infrequently display, while tripling their feeding rate to put on weight and energy reserves for the coming winter.
Anole mating behavior
When the day lengths become short and air temperatures are low, the A. carolinensis population leaves its home ranges and seeks out winter retreats (e. g. , root masses, rock crevices, even under house siding). On warm days in the winter, aggregations of males and females may emerge to bask, but they rarely feed or interact socially. Early in March, with warmer air temperatures and longer day lengths, the anoles will leave their winter retreats and disperse into springtime home ranges. There feeding begins along with hormonal changes that initiate reproductive behavior and reproduction. By early April, the population begins the next 4-month breeding season. Though more data are needed, it is probably rare that an average adult breeds more than two years.
Should you consider holding A. carolinensis for observation, you should be aware of their needs in advance. For most people, green anoles need more than can be easily supplied, especially for long-term care. Basically this means they are best left "in the wild," and not held in captivity. Here are some considerations. During the breeding season, do not house two males together. They are certain to fight and become stressed. A male with a few females would work well. However, an all-female group will also bring out the territorial interactions, even in the less aggressive females. Next, consider that the enclosure that is used almost certainly will be much more cramped that the approximate the size of the natural home range; for a male, this is a volume of 12 feet high x 12 feet wide x 12 feet long (4 x 4 x 4 m). Anoles are arboreal, and I have seen them as high as 100 feet up in mature hardwood forests. Therefore, the more complex the perches, branches, and vegetation for climbing, basking, and hiding, the better. Anolis carolinensis needs heat (but not too much heat). Cage temperatures should cycle between about 23-35 C (73-95 F). Light intensity and quality are also important. A combination of incandescent (for heat) and fluorescent (for brightness) lighting that includes some UV wavelengths works well, but it is obviously not the same as the characteristics of actual sunlight. Water should be made available by daily misting of vegetation, and from standing or dripping water sources (e.g., shallow dish of fresh water). Calcium lactate, especially for females during egg laying, and other mineral supplements are required. These can be dusted onto cultured food (e.g., crickets and mealworms) or onto field sweepings. It is important not to release prey (e.g., crickets) that are too large to eat because at night these insects will become active and chew on sleeping lizards. The most preferred food is soft-bodied, such as spiders and small caterpillars. Do not feed hard-bodied prey, such as sowbugs or beetles.
Clearly, the green anole is not just another dime store disposable pet. For many of us, the green anole gave us our first encounter with pet reptiles, often more to the anole's detriment than ours due to ignorance about its needs and habits. Ultimately, its slender beauty and curious social interactions are best observed under natural conditions.