Anole Annals

This was tweeted by Gretchen. What’s the story?

An actively foraging anole on the prowl (A. tigrinus; photo by J. Losos)

Nearly 50 years ago, Eric Pianka proposed the idea that hunting animals forage in one of two ways, either actively foraging for prey or sitting-and-waiting for food to wander by. These ideas were initially promulgated with lizards in mind, and much of the research in the last half century has involved lizards. Anoles haven’t been a major player in the work, but their certainly have been some studies conducted on anoles.

This post is motivated by a paper published by Cooper et al. in Herpetology Notes last year in which new data are presented on six anole species, as well as for a variety of other species. The anole data conform both to previous data on the same species and studies on anoles in general: as lizards go, anoles are on the sit-and-wait end of the spectrum, moving relatively little (think about the other end of the spectrum, species like whiptail lizards which seem to move almost non-stop).

I was surprised in looking through the archives to see that we haven’t previously had a post on AA about foraging mode. Now we do! And for some background: I reviewed what we know about anole foraging in a five-page section of Lizards in an Evolutionary Tree. The take-home messages:

1. By comparison to other lizards, anoles don’t move much and would be considered sit-and-wait foragers;

2. Nonetheless, among anoles, some are much more active foragers than others;

3. Caribbean anoles are much more active than mainland species;

4. Much remains to be learned about the specifics of anole foraging and how it differs among species

And here are some highlights, from the footnotes:

“Some of the danger inherent in an active foraging mode was apparent in another observation of a female [A. valencienni] moving upside down on a bromeliad, searching for prey (quoting from Trivers’ field notes, p. 575): “. . . it seems to spot something on a neighboring bromeliad, also upside down. I too spot something on the second bromeliad. Starts to dart the 5 cm to the neighboring bromeliad but—as if forgetting it is upside down—it steps into thin air and falls 6 m to the ground. It appears to be uninjured.”

“Examples of this prey-catching behavior were provided for the relatively short-limbed A. carolinensis (under the name A. principalis) by Lockwood (1876, p. 7): “I have just been watching Nolie eying a fly which was walking on one of the glass panes of his house. He made a noiseless advance of about three or four inches; then followed a spring, when he was seen cleaving to the glass by his feet, and champing the captured fly. I saw him once intently watching the movements of a fly which was walking on the glass. As seemed evident to me by an ominous twitch of that little head, his mind was made up for a spring; but lo, there was a simultaneous makeup of mind on the part of the fly, which at this juncture flew towards the other side of the case. Then came—and how promptly—mental act number two of Anolis, for he sprang as the after-thought directed, and caught the insect on the fly.” Dial and Roughgarden (1995) report an anole jumping from a branch one meter above a spider web, catching the spider as it passed by, before landing in the vegetation below.”

We’ve noted before that little is known about dewlap use by females. Here’s a video of green anoles mating in which the female periodically bobs her head and occasionally sticks out her dewlap.

Arthur Loveridge was one of the great scholars of African herpetology, and a fascinating individual, curator of the Museum of Comparative Zoology for 33 years. AA has recently come across a pdf of his obituary written by Ernest Williams, who succeeded him at the MCZ.

The obituary is fascinating not only because it details the career of an important, yet quirky, individual in our field, but also marks how the profession of museum curator has changed markedly from the days in which curators were wealthy amateurs, popping around to satisfy their curiosity. Of course, I’m sure Loveridge’s sentiments would find happy agreement today: “Probably only a zoologist can look at an uncaught cobra and feel the joy a child feels on Christmas morning.”

The paper’s worth reading for the various stories about the “Demon Curator,” including the drawer labelled “string too short to use” and the famous footnote in the 1957 Loveridge and Williams turtle monograph.

Anolis transversalis, female on the left

We’ve talked previously about anole species that differ in the color of their dewlaps, but I don’t recall any discussion of species in which the males differ markedly in body patterning. Certainly, that happens a lot. For example, we’ve talked a lot about polymorphisms in female back patterns, but in most of these species, the males don’t have any of the patterns shown by the females. And in this case, and many others, one sex is patterned and the other one pretty much isn’t.

In any case, Anolis transversalis is a great example of a species in which both sexes are patterned, but differently. And to boot, their dewlaps are differently colored as well. What a species!

Does anyone want to suggest–or better yet, supply photos–of other species in which both sexes are patterned, but differently?

Recently, a 2006 paper on giant land tortoise dispersal has been going around social media. The story is that a tortoise from Aldabra, a tiny speck of an island north of Madagascar, washed ashore in Tanzania, some 700+ kilometers away. Barnacles encrusted on the tortoise’s legs suggest that the chelonian had been adrift for 6-7 weeks, an estimate that makes sense given the prevailing currents. The article summarizes several other, not-quite-so-well documented, cases of tortoise dispersal. These stories make clear that tortoises can disperse over long distances of open ocean. Thus, it is not surprising that they occupy far-flung islands around the world (and remember that until the onslaught of humans, they used to occupy many more islands, such as Madagascar, Mauritius, and New Caledonia).

This is all well and good, but why discuss it in Anole Annals? After all, our little four-legged friends weigh a few grams, not many kilograms, and they don’t carry a flotation device on their back. Does the dispersal ability of these behemoths tell us anything about how anoles reached their island homes?

Let’s go to an example closer to home, from a paper in 1998 published by Ellen Censky in Nature. In that paper, Censky et al. reported an observation from 1995 of a large mat of vegetation washing ashore on the Caribbean island of Anguilla (described as “a mat of logs and uprooted trees, some of which were more than 30 feet long and had large root masses. Local fishermen say the mat was extensive and took two days to pile up on shore.”). This in itself was not so unusual—such mats wash ashore regularly, especially in hurricane season. What was unusual is that riding this vegetation was a passel of green iguanas, a species native to some islands in the Caribbean, but not Anguilla. As onlookers watched, the vegetation washed ashore and, like tourists disembarking from a cruise ship, the 15 iguanas stepped off onto the beach. And like the occasional tourist, the iguanas liked it so much that they never left. Rather, they settled, put down roots, and raised a family. As far as I know, the iguanas are still there to this day.

But where did they come from? One bit of information did not make it into the article, but Ellen Censky has kindly allowed me to report it here. There was a clue in the mat of vegetation, in the form of a street sign. In French! That narrowed the possibilities considerably, and a bit of sleuthing established that the street sign, and hence the saurians, came from the island of Guadeloupe, where iguanas are native, and where Hurricanes Luis and Marilyn had struck some weeks before. Hurricanes often knock enormous amounts of vegetation into the water, explaining the formation of the vegetation mat.

True, iguanas are bigger than anoles, but otherwise this is exactly the mode of transport hypothesized for anoles. For example, large amounts of vegetation often fall into the Amazon and Orinoco Rivers in South America and end up floating far out to sea, as chronicled by Blair Hedges in a paper a while back. It’s not that hard to imagine a female, with eggs or storing sperm, hunkered down in such vegetation and managing to survive such a journey. It probably doesn’t happen often, but as Ernest Williams pointed out in an overlooked paper on colonization years ago, given millions of years, the unlikely becomes probable. Phylogenetic evidence indicates that the Caribbean anole radiations are the result of two colonization events from the mainland. In addition, it suggests that the Norops radiation on the mainland is a result of back-colonization from the islands—over the 40 million plus year history of anoles, that doesn’t seem very unlikely.