Anole Annals

Anolis barkeri. Photo by J. Losos

As part of its ongoing studies of Central and South American anoles, Team Mainland—fresh off successful field work in Colombia and Venezuela earlier this year, traveled to the Veracruz, Mexico to sample that state’s anole fauna. Joined by Anne-Claire Fabre, Victor Jiménez, and Ramón Martínez, Team Mainland worked at the fabled Estación de Biología Tropical Los Tuxtlas, home to eight or nine (depending on which paper you read) species of anoles. The goal of the trip was to characterize the ecology, behavior, and morphology of the species residing at the station. Although all anoles are interesting in their own right, as we know, not all anoles are created equal. And, indeed, there was one special species we had our heart set on seeing: the large aquatic anole, Anolis barkeri.

Anolis barkeri. Photo by J. Losos

Anolis barkeri. Photo by Victor Jimenez.

And lo and behold, we saw them! Aided by Bob Powell’s advice to visit his old field site, a lovely stream located several kilometers from the station, we spent several days observing the antics of these gorgeous anoles, the largest of the mainland aquatics. And by antics, I mean primarily sitting around doing nothing, though they did flash their gorgeous red dewlaps occasionally (alas, not caught by camera, but several times on video—stay tuned once they get processed). Actually, they were sometimes quite active, running rapidly from one place to another. Like other mainland aquatics, these guys hang out right next to streams, and when threatened will sometimes jump in. They don’t go swimming away, though, at least not in our observations (which agree with others); rather, they immediately go to the nearest water-land interface and hang out, hoping they have not been detected.

Our trip occurred in early August, at the end of both the reproductive and dry seasons. We were told that it had been a particularly dry dry season, which may explain some of the observations. For example, A lemurins is supposed to be very common, but we didn’t see a one. Also, males of two other common species, A. sericeus and A. rodriguezi, were few and far between. This was surprising, but perhaps these—like many mainland species—are primarily annual, that is, with a lifespan averaging less than a year.  Perhaps the males, spent by their exertion, are all dead, explaining why we saw so few of them. That was a classic hypothesis borne of field observations, but the Malice of Nature did not intervene to refute it. A number of people suggested that A. barkeri is only found in shaded streams; in the open, it is pushed out by basilisks. “Find a basilisk,” we were told, “and you won’t find A. barkeri.” For the record, we did find several small basilisks along the stream, though only in open, sunny spots in the otherwise well-shaded watercourse. The A. barkeri were found on logs and rocks, always near the water. They didn’t impress me as brilliant swimmers, but could immediately climb onto rocks—very good graspers, with long arms and sharp claws.

I was particularly curious to learn more about A. sericeus.

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Anolis gundlachi. Photo by Alejandro Sanchez.

Anolis gundlachi 10 seconds later. Photo by Alejandro Sanchez.

West Indian photographer and natural historian extraordinaire Father Alejandro Sanchez sent in these photos, commenting “I took these two pics less than 10 seconds apart from each other – the time it took for me to modify the flash’s settings. Yet the lizard noticeably changed color patters in such a short time, surely for being scared by my proximity. Anolis gundlachi is one of my favorites.”

And note those blue eyes!

Broken Caribbean termite nest.  These termites may infect anoles with a thorny-headed worm parasite, Oncicola venezualensis.

Among the many anole parasites are the acanthocephalans, or thorny-headed worms, which in anoles are typically found as encysted larvae in the body cavity, muscle, or under the skin. One of these acanthocephalans – Oncicola venezualensis – is relatively common in anoles on the Puerto Rican Bank, and is the main character in one of my favorite anole-parasite stories. The story has three parts: 1) how the parasite gets into anoles, 2) how it continues its life cycle beyond anoles, and 3) the mystery of when it all began.

In addition to anoles, O. venezualensis larvae occur in the Caribbean termites Nasutitermes acajutlae on the Puerto Rican Bank, which is a partially submerged landmass comprised of Puerto Rico and all the Spanish, U.S., and British Virgin Islands except St. Croix. These termites construct protective nests and foraging tubes in which they live (see photo), and each individual termite belongs to a morphologically distinct caste. Most are in either the soldier or worker caste, and soldiers are larger than workers, aggressive, and armed with big mandibles. These two castes also have slight color differences – worker termites have yellow heads, whereas soldier termites have dark yellow heads.

Anoles eat termites, and O. venezualensis manipulates both the behavior and appearance of its termite hosts in order to increase the likelihood that the parasitized individuals will be preyed on by anoles (Fuller et al. 2003). Infected termites behave carelessly when compared to their uninfected peers. When a foraging tube is broken, for example, the parasitized workers arrive quickly and then linger, a behavior that makes them more susceptible to predation by anoles. Infected termites also look different, as the head color of infected workers changes to a pale yellow. This increases the difference in appearance between the parasitized workers and the aggressive soldiers, and anoles presumably try to avoid eating soldiers (remember that anoles are smart decision-makers!). The color-changing strategy is effective – in feeding trials with Anolis cristatellus where the lizards were presented with petri dishes containing both parasitized and parasite-free workers, the lizards consistently preferred the light-colored parasitized termites.

After the anole ingests a termite infected with O. venezualensis, the parasite encysts (i.e., forms a cytacanth) somewhere outside of the host’s gastrointestinal tract. In anoles it remains in its larval form, unable to complete its life cycle, and waits for the lizard to be ingested by its definitive host where it will mature into an adult and undergo sexual reproduction. The identity of O. venezualensis‘s definitive host remained elusive for some time. Two primary suspects were mongooses and the pearly-eyed thrashers, since both eat anoles and are common on the Puerto Rican Bank. But, O. venezualensis remains in its larval form in both of these hosts (Nickol et al. 2006). The mystery was solved a couple of years ago – it’s cats! Fuller and Nickol (2011) necropsied a feral cat on St. John and found 87 adult worms. The life cycle for O. venezualensis is now understood to be termite → lizard or bird → cat, then begins again when termites ingest parasite eggs in cat feces. The mongooses aren’t eaten by cats, and so are dead-end hosts for the parasites.

For me, learning that the cat is the definitive host was a head-scratcher. We know that cats eat anoles, and feral cats are abundant on the Virgin Islands, particularly St. Thomas. But, it’s hard to imagine how a parasite with a complex life cycle of at least three hosts (termites, anoles/birds, cats) became invasive across so many islands. It’s also possible that a different, native anole-eater also serves as the definitive host. Bats are the only extant native mammal species on the Virgin Islands, and we know that some bat species eat anoles. Perhaps bats are the original definitive hosts? In any case, the populations of O. venezualensis have likely increased in recent times due to the introduction of cats on those islands, and whether that’s had any effect on the anole populations is unknown.