Brown Anole

ReptileCaribbean

Nov 23

Anolis sagrei

A brown anole male can sometimes be spotted doing "push-ups", often with his orange-red dewlap — or "throat fan" — on full display. This performance can either be threatening or seductive, depending on the context, as he will do this to both scare away rivals and attract females.

Invader Anoles

The brown anole is a hardy and intrepid explorer — or invader, depending on how you look at it. It originally set sail from the Caribbean, where it is native to Cuba, the Bahamas, and many smaller surrounding islands. As more humans began to move between these islands and the rest of the world, these lizards tagged along for the ride; sneaking aboard cargo ships as stowaways or charming visiting humans who then took them abroad as pets. Either way, the anoles had made their way to mainland America and now populate the humid, semi-tropical forested areas of Florida and Mexico, further extending to Georgia, Texas, and southern California, as well as colonizing islands like Hawai'i and Jamaica. It has even made its way, through anthropogenic means, to such far-flung places as Singapore and Taiwan.

Now, it is well known that invading species can often lead to great suffering for the locals. One only needs to look at apocalyptic cases such as those of the cane toad — the toxic plague spreading across Australia — or the common myna — the yellow-faced bully of the bird world, that has spread far outside its Asian range. The brown anoles are not such harbingers of death (at least not yet), but their impact is still noticeable.

As is expected, the species with the most similar niche to this tough and adaptable colonizer suffers the most. In North America, this happens to be its close cousin, the green anole (Anolis carolinensis) This more stylish anole — with its longer verdant body, light pink dewlap, and the ability to change colours like a chameleon — is outcompeted anywhere its range overlaps with the brown. Eating from the same larder — both diets comprise mainly of insects and spiders — the green is left hungry while the voracious brown eats. In this reptilian war, both species engage in "intra-guild predation", meaning that they eat each other's hatchlings. The browns just seem to be the fitter fighters. On islands such as Hawai'i, where ecosystems are more specialised and fragile, they bring pestilence; transmitting parasites to local lizard populations. They are now also one of the most abundant reptiles in Florida. The ecological consequences of their march across North America are still unknown.

This seems pretty bleak — and for the green anoles and Hawaiin lizards it may be — but the ecological impacts of the brown anoles aren't all bad. For any arachnophobes living in southern North America, it is thought that these plentiful lizards are responsible for keeping the spider population in check, as well as feasting on pests like cockroaches. On the other hand, it is also thought that some larger species of spider depend on these anoles for prey. To humans, the brown anole is a minor nuisance at most as their populations increase in urban areas. Many invite them willingly into their homes as pets. There currently don't seem to be any major efforts to cull this invasion, in fact, it seems that these lizards are so numerous and hardy that the most we could do would be to slow them down.

A Model Study Species

The same characteristics that make brown anoles such effective invaders, also make them model organisms for studying evolution by natural selection. Anole lizards populate most of the islands of the Caribbean, and if Darwin were to have first disembarked on these islands, we may now be talking about "Darwin's anoles" rather than "Darwin's finches". Just like the finches of the Galapagos, the anoles of the Caribbean showcase a multitude of different traits and behaviours while living alongside each other. While the Galapagos finches evolved differing beaks to take advantage of different types of food, the anoles evolved different morphologies and lifestyles — with some anoles living on the leaf-littered forest floor, others on the trunks and in the branches, while others dominate the very crowns of trees in the canopy. This is an example of what is called "niche partitioning", where similar species can exist alongside one another by specializing in different niches so as to not exhaust the food supply or living space.

These anoles also exhibited a great example of convergent evolution. On almost every island, the species that inhabit the same niches — say, those that lived among grasses on the ground — were almost identical. It could be speculated that one "grass-dwelling" ancestor spread to all the islands, but the genetic evidence points in another direction. The "grass-dwellers" were more related to the behaviourally and morphologically different species on the same island rather than to other "grass-dwellers" on different islands. The traits that make these anoles good at living in the grass — such as shorter legs for grasping onto more narrow perches — evolved separately on each island but converged because those traits offered the best chances of survival for that particular lifestyle.

The brown anole has been purposely transplanted onto islands to study the effects of different environmental conditions on its evolution that can be seen over a much shorter time period — observable in a human lifetime, as these anoles become sexually mature at a year of age. Introduced to twenty islands, the hardy species flourished on all but the smallest, which were ravaged by catastrophic events like hurricanes. Over the generations, the morphology of the brown anoles on each island changed and diverged from one another, adapting to the different vegetation on each island. On islands with many trees that offered broad peching surfaces, the length of legs increased, while on those with mostly grasses and herbs, legs became shorter to allow for grasping narrow perches. Serving as living test cases for evolution in action, these brown anoles demonstrate how — given enough time apart in differing environments — one species can diverge into several, varying in behaviour and appearance.

Life & Love

The lizards of the genus Anolis partition out niches that span from hiding among tree roots to crawling through the tops of forest canopies. The brown anole is a "base-of-tree specialist". It sits low on tree trunks and rocks, or in urban areas, on fences and buildings. Active during the day, it alternates between sunbathing and searching for arthropod prey. Its territory, about the size of a big bush, is a communal area shared by several anoles. This setup is fairly stable until the breeding season rolls around, when the males go from fairly calm neighbours to aggressive rivals.

If two male anoles find themselves sitting on perches at different heights, they are likely to initiate a head-bobbing "push-up" contest while extending their bright dewlaps. But if they find themselves on the same perch and of similar sizes, flashy displays are not enough and often more violent battles take place as they directly attack each other. The heftier males with the more impressive dewlaps are often the victors of male-on-male confrontations.

The prize for these victors is a larger territory with more mates. While the reproductive habits of the brown anole haven't been extensively studied, those of their unfortunate green cousin have — given their relatedness, they probably breed in similar ways. The way for these anoles is called "female-defense polygyny", meaning that one male defends a territory that houses several females. A female who wants to mate will put herself on display for the male, making herself seen by cocking her head up and down. He will then rush over and give her a love bite on the back of the neck. If he is in the mood, they will proceed to copulate for 30 to 60 minutes. The female will deposit her one or two eggs now fertilized eggs into a small hole in the moist soil. Beyond this point, parental care is non-existent. Six to eight weeks later, the hatchlings see light and breathe air for the first time, relying entirely on instinct to catch prey and avoid becoming it.

📍 Gardens by the Bay, Singapore 📅 2 November, 2023
I've never been to the Caribbean, and so haven't seen a brown anole in its native habitat. Those I have seen are invaders that had made their way all the way to Singapore. They scuttle through the bushes and sunbathe on the stones below the biomimetic Supertrees of the Gardens by the Bay.
Unfortunately, I wasn't able to get a photo of one showing off his distinctive dewlap. One of the anoles did begin to do "push-ups" at me, but I guess that I was either not threatening enough or not attractive enough for him to warrant extending his colourful throat fan.

**Where Does It Live?**

⛰️ Humid, semi-tropical forested areas. Sits low on tree trunks and rocks, or in urban areas, on fences and buildings.
📍 It is native to the Caribbean; Cuba, the Bahamas, and many smaller surrounding islands. Invasive in the U.S. — Florida and Mexico, further extending to Georgia, Texas, and southern California, as well as colonizing islands like Hawai'i and Jamaica, even farlung Singapore and Taiwian,

Size // Small
Length // 12 - 21 cm (4.7 - 8.3 in)
Weight // 4 - 8 grams (0.14 - 0.28 oz)
Activity: Diurnal ☀️
Lifestyle: Solitary 👤
Lifespan: Up to 5 years in the wild
Diet: Omnivore
Favorite Food: Insects & spiders 🕷️
Class: Reptilia
Order: Squamata
Family: Dactyloidae
Genus: Anolis
Species: A. sagrei

The brown anole is considered to be one of the most invasive reptile species in the world. It is estimated to have invaded Florida 6 individual times in the 1940s and became firmly established by 1970.

The skin flap below its chin is called a dewlap — it is used in courtship and aggression displays, as well as to cool down or warm up.

Copulation begins with the male giving the female a bite to the back of her neck and can last from 30 to 60 minutes.

Like the finches of the Galápagos Islands or the honeycreepers of Hawaii, the lizard of the genus Anolis serve as a reptilian case study of adaptive radiation, throughout the Caribbean islands.