Jonathan Losos, professor and curator of herpetology at Harvard?s Museum of Comparative Zoology, writes from Colombia, where he is studying the biodiversity of anole lizards, an evolutionarily successful group that has produced 400 species throughout Central and South America and the Caribbean islands. For more on anoles, see anoleannals.org.
March 1, 2013
For 25 years, my research has focused on the evolution of Anolis lizards on islands in the Caribbean. That means I travel there several times a year. Whenever I tell people about my research, I can almost predict what they?re thinking. They valiantly attempt to suppress a smile as they picture me lolly-gagging on a beach, settled into a hammock and sipping a Mai-Tai. Here?s the problem with that: on Caribbean islands, anoles live just about everywhere except on the beach. And so, despite years of field work on these lizards, a day at the beach has never been part of the itinerary.
Until now that is. After spending a week in the chilly Andean mountains of Colombia, Rosario Casta?eda, Anthony Herrel and I have put away our sweatshirts and arrived in Maracaibo in the hot and dry northwest corner of Venezuela.
Our goal: to study the only known beach anole, Anolis onca. We were joined by two of Venezuela?s leading herpetologists ,Tito Barros and Gilson Rivas, who have extensive familiarity with this species, and several of their students. There?s no common name for this lizard, so I will just refer to it as the beach anole.
You might think that as the only anole to live on beaches, this lizard must possess some unique anatomical feature that adapts it to such a lifestyle. You would be right. This species sports beach footwear. Or more specifically, it lacks the sticky toepads common to all other known species of anole. The reigning hypothesis is that this species underwent an ?evolutionary reversal? as it adapted to life on the beach. Toepads are covered with millions of microscopic hairs ? not much help for traction when you?re standing on millions of tiny sand grains. So the thinking goes that it just shed them over evolutionary time.
Several surprises greeted us at our first study site on the shore of Lake Maraicaibo. First, we found few lizards at sites colleagues had recommended for their dense populations. Our initial morning foray yielded one lizard, though the afternoon session at a different site produced a half dozen more.
I thought the scarcity might be explained by our second surprise: extremely strong winds. The literature had warned that the beach anole seems to occur only in windy places. Still, we weren?t prepared for such a pummeling. And in my experience, the combination of scorching temperatures and strong, dry winds does not bode well for lizard-finding. Normally, small reptiles tend to reduce activity during such an environmental onslaught to avoid becoming dehydrated. Even an anole?s tough, scaly skin cannot prevent water loss in such conditions. But our colleagues assured us that this could not be the explanation, because the wind was normal for the area. ?That suggests these lizards have a special ability to hold onto moisture. All the more reason to study them ? if only we could find a few.
Our colleagues provided an alternative explanation for their general absence: the region is currently experiencing a very severe drought, and this, rather than the wind, could be responsible for the spotty sightings. (Whether the population has decreased or the lizards are simply hunkered down is unknown ? either option could be a result of drought conditions.)
That?s the way fieldwork plays out ? you make plans month in advance, hope that the weather cooperates, and make the most of it when it doesn?t.
And so we did, eventually finding a moderate number of lizards. But our biggest surprise was where we actually found them. Despite their billing as sand anoles, we never saw a lizard on the beach. Most were perched on or moving about the vegetation, except for a few on the ground in grassy areas. The literature reminded us that the beach anole has been reported in the vegetation in the past. But we were not expecting to find them almost exclusively off the ground and away from sandy substrates.
Nonetheless, we did make some interesting new observations about the biology of this species. Most had stomachs packed with leaves, something never reported before among the other 400 anole species. In addition, the blue coloration in the corner of their mouths is also unique among these anoles, though known in other lizards. Their differences in diet and color, combined with their sand-loving toes, make this one of the most unusual species in this evolutionarily diverse group of lizards.
But our data don?t tell us why they lost their toepads. Of course, we may be looking at the wrong time or wrong place. Maybe the lizards only use sandy surfaces during some seasons or circumstances. Or perhaps the ancestral beach anole lost its pads when it started living on sand dunes, and subsequently some populations have given up their sand-dwelling ways. Or perhaps the loss of toepads is unrelated to the ground the lizards walk on. Perhaps it has to do with the excessive windiness, though I can?t think of a good reason why it should.
You win some, you lose some. That?s what science is like: sometimes you don?t get the answers you were seeking, but instead make discoveries about something entirely different.
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