Category: Notes from the Field Page 9 of 22

Did the lizards on this island survive Hurricane Sandy?

Long time AA readers will recall that every year, a team of researchers go to the Marsh Harbour, Abaco, Bahamas to study how curly-tailed lizards affect brown anoles and, in turn, how the presence of brown anoles affect the rest of the ecosystem on tiny islands. This research, initiated by Tom Schoener and Dave Spiller in the 1980s, has been long-lasting and has produced many interesting discoveries about anoles, ecology and evolution.

But in the last few years, the research has been bedeviled by hurricanes. In 1998 and then again in 2004, studies on the effects of curly-tails on brown anoles were terminated prematurely by hurricanes. We did learn a lot about how hurricanes affect ecosystems, including lizards, but it wasn’t so helpful with regard to understanding how brown anoles evolve in response to predation pressure. After waiting several years for the islands and lizard populations to recover, we re-initiated the experiment again in 2008. At the same time, we started a second experiment by introducing a single pair of lizards to each of seven islands, creating a replicated experiment on the effects of founder events on evolutionary adaptation.

Both experiments were moving along nicely when—what else?—another hurricane hit, Irene in 2011. As everyone recalls, Irene was a big one, and we feared the worst, but by good fortune, its effects were less than catastrophic because it hit at low tide—minimizing the extent of the storm surge—and from a direction that tended to minimize the storm surge on the particular islands we were studying. The result was that some—though not all—island populations were hit hard, but very few were demolished. In fact, I speculated that studying the effect of a population bottleneck on populations created by founder events might be particularly interesting, because some theories suggest that it takes multiple population crashes to lead to great evolutionary changes.

Hurricane Irene ripping its way through the Bahamas. Abaco is the island to the right of the arrow labelled “Freeport.”

So along comes 2012 and… another direct hit on our islands, this time by the infamous Hurricane Sandy. Although initially quite large, by the time Sandy hit Abaco, its wind speeds were less than Irene, giving  us hope. But, on the other hand, Sandy slowed to a crawl, meaning that it remained over Abaco for a long time, not just at low tide, and also from a more threatening direction than Irene’s. All dangerous portents.

Photo by Jason Kolbe

Thus, with great trepidation, we returned to Abaco earlier this month, anxious to learn how our island buddies had fared. A trip to Abaco last December—admittedly, not the best anole time, even in the Bahamas—had indicated that a number of the lowest lying islands seemed lizardless. And our visit confirmed that finding. The seven islands in our founder effect study are all small and low-lying, and the lizard populations on five of them were wiped out (one of them had a female last December, but she’s apparently gone). One of the remaining islands contains but three anoles—a male and two females—and it will be interesting to observe the effect of this population bottleneck. That population—like all in this experiment—was founded by two individuals and quickly grew in size. Will it rebound again, and just as quickly?

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What’s going on inside their heads? The four anole species of South Bimini, The Bahamas.

Whenever I stand in the forest on South Bimini in the Bahamas, I’m always struck by the similarity of these anoles to those I’ve worked with elsewhere in the Greater Antilles. Yes, that’s the whole idea behind the ecomorph concept, but as many have pointed out recently, habitat use and morphological convergence are only part of the story. Along with the classic divergence and convergence in body size and shape, the ecomorphs also show intriguing convergence in sexual size dimorphism and social behavior. It’s this latter aspect of the Caribbean anoles that interests me. How has this convergence in behavior, though it’s not perfect, happened? Have the proximate mechanisms that are responsible for anole behavior evolved in the same way on the various islands in the various ecomorphs? From a larger perspective we are asking, how do neuroendocrine systems evolve? That’s what my students and I are trying to figure out, and that’s why we’re in the Bahamas right now.

A few years back, Matt Lovern and I started a project examining circulating steroid hormone levels in four anole assemblages (The Bahamas, Puerto Rico, Dominican Republic, and Jamaica). Based on a plethora of work in a variety of vertebrate species and their testosterone-behavior relationships, we predicted that we would find consistent intra-island differences among ecomorphs in testosterone (and corticosterone), with the ever-charismatic trunk-ground anoles showing the highest levels. Boy, were we in for a surprise. We did find species differences, and we even found consistent ecomorph differences, but not like we expected. Unlike the mainland green anole (Anolis carolinensis) and the introduced brown anole (Anolis sagrei) on the mainland (yes, the apparent difference in testosterone levels  between mainland and Caribbean brown anoles is probably a separate, interesting story!), trunk-ground anoles in the Caribbean have very low baseline testosterone levels. Twig anoles, on the other hand, are super-juiced with testosterone. I won’t give the whole story away, as we are working on getting it published, but the take-home message is that hormones are only part of the story, and testosterone likely plays very different roles in the behavior of the various species and ecomorphs. While this may not sound surprising to some, in some ways it is, because typically people only focus on circulating hormone levels to explain behavior, and testosterone levels tend to be pretty good predictors at a large scale. Although many proclaim that it’s not the hormones but the receptors, nobody has examined hormone receptor distributions in target tissues across a large number of closely related species. Again, that’s what we’re trying to do here in the Bahamas (and elsewhere).

We’ve been spending our time here on Bimini collecting brains for analysis of several potential regulators of social behavior in multiple brain regions known to be important in anole aggression and courtship behavior. My student Allison, who is here with me now, got some funding to spend the rest of the summer back in Minnesota sectioning and staining brains from the four ecomorphs here on Bimini. We’ve also been conducting “GnRH challenges” on these species to determine whether the baseline levels of testosterone that we’ve measured are as high as they can go. That is, when we physiologically stimulate the hypothalamus-pituitary-gonad axis to produce more testosterone, is it capable of doing so, and are there differences among species in that response? I’ll be spending the rest of my summer running those samples to find out. This will complement the social challenges that Matt Lovern and I conducted in the Dominican Republic last year on Anolis cybotes and Anolis coelestinus, examining whether social challenges result in increased testosterone. Stay tuned to see what we find!

A windy study site on the northwest coast of Venezuela.

All of us who study anoles in the Caribbean share a PR problem: people think we’re partying on the beach all day long. Now, it’s true that that’s exactly what some of my colleagues do (you know who you are, but I’m not naming names), but there’s a problem with this approach: anoles don’t live on the beach! And for that reason, anole researchers generally do not either, at least not during working hours.

The padless foot of Anolis onca. Photo by J. Losos.

As we all know, anoles are characterized by the possession of two characteristics, an extensible throat fan and expanded subdigital toepads. But there are exceptions. The Cuban A. vermiculatus and A. bartschi (two of the finest anoles you’ll ever come across) have no dewlap whatsoever. And one species, A. onca, entirely lacks toepads, not even a hint of subdigital lamellae.

Where am I going with this, you might wonder? The answer is simple. Where do you think A. onca lives? On the beach! Anolis onca is the only beach-dwelling anole, or so it’s said. And for that reason, our South American Little Known Anole Tour (SALKAT) moved from the chilly Andes of Colombia to the smoking hot sealevel of Maracaibo, Venezuela to see what’s up with this species.

Current exchange rate, 6.3 Bolivares (Bs) to the dollar.

A few notes about Venezuela. Well,  one mostly. It’s incredibly expensive. Who would pay $10 for a box of Froot Loops? Not even me. Or $9 for a can of Pringles? Ahem, well, it had been a good day. Rental cars cost more than $200/day, if you can find one (when we tried to get one at the Caracas Airport, the six rental car booths had, between them, two cars available). And hotel rooms are exorbitantly priced and also in scarce supply. We were told that the reason for that is that they were full of Cuban workers, sent over by the Castros to help their socialist brothers-in-arms. And, to be honest, the people we encountered–in the airport, at the hotel, etc.–often weren’t the friendliest.

One thing was cheap, though, gasoline. They practically give it away. At one point, we only had 1/4 tank of gas, so stopped at a service station. I went in and bought a can of soda for $2.50, then paid the bill for the gas, which came to $0.60.

Anolis onca. Photo by J. Losos.

Any way, back to A. onca.

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Old male passed over winter, tough overlord

For several years now, I have been noticing that Anolis carolinensis has been making a dramatic comeback in south Florida.  In the last five years or so their numbers have exploded.  Their resurgence began in the Florida Keys and they have been working their way north, recently reaching south Miami and now entering into central and northern Miami-Dade County. Unlike the original population of carolinensis, which favored rural environments, this new population is bold and holds its own against sagrei, still dominating the trunk-canopy, but ranging all across different ecological niches including completely urban environments (which carolinensis did not). However, these are simply field observations and conjecture on my part.  Having said that, my theory is that they are actually a vigorous carolinensis-porcatus hybrid.  I believe this not only because of their robust physical constitution when compared with the original carolinensis, but also because some within the population have the scapular ocellus normally found in porcatus while others in the same population do not and many have the white outline (like the old male in the picture), but not the inner dark portion of the ocelli and vice-versa.

Two contenders to take over turf (probably both offspring of old male). Notice one has prominent “eye-spot,” the other (victorious male) does not.

The brown booby, one of the denizens of Great Swan Island.

The Swan Islands, three tiny outcroppings of petrified reef jutting out of the otherwise open stretch of water between Cuba, the Cayman Islands, and Honduras, hold one of the least-known populations of Anolis in the Caribbean.  A visit by George Nelson in 1912 established that anoles are present on both the larger Great Swan Island (larger is a relative term – the entire island is about 5.5 square kilometers) and Little Swan (which is about half that size).  The specimens collected by Nelson were later examined by Barbour at the Museum of Comparative Zoology at Harvard and found to be closely related to A. sagrei – they were designated as a species, A. nelsoni, notable mainly for its exceptionally large size.  They were later relegated to a subspecies of A. sagrei by Ruibal.

Aside from a visit by Brad Lister in the early 70s, the anoles of the Swan Islands have been left in relative peace by anolologists.  That is, until last December, when I joined a team including Jonathan Losos, Randy McCranie and Leo Valdes Orellana that set out to visit the Swan Islands to learn more about this mysterious member of the anole clan.

Getting to the Swan Islands turns out to me much easier said than done.  The island has been uninhabited for decades, except for a handful of rotating members of the Honduran Navy who are stationed there to keep drug smugglers from using the island as a way station.  The only way to contact the island is by radio, with the cooperation of the Honduran Navy.  The only way to reach the island is by chartering a private plane or boat.  And getting permission to fly there required a week of wrangling with the authorities in La Ceiba, Honduras.  With the help of local contacts in the police and the intervention of a lawyer, we were ultimately able to get the necessary permission, first from the head of the armed forces for all of Honduras, and then by the heads of the Air Force and the Navy, respectively.  Once we had permission, we managed to charter a small plane to the island, stocked up on rice, beans, water and batteries (the islands have no electricity or running water), and were ready to go (minus Jonathan, who couldn’t last out the wait for permits and had to return to the U.S. to grade final papers).

Big Swan Island

Swan Island from the air. Photo by Alexis Harrison.

Our first view of the island from the air revealed rugged cliffs and open beaches, dense forest, and decaying buildings overgrown by vegetation. We landed on the grassy runway that dominates at least a quarter of the area of the larger island and were greeted by seven armed members of the Honduran Navy and one friendly dog.  Despite the guns, the Navy was very welcoming and helpfully carried many of our supplies to the main camp, where they had barracks and a kitchen, and where we could work at an indoor picnic table and could pitch our tents.  After some minimal unpacking and setting up, we set off to get a feel for the island.

Luxury accommodations, Swan Island style.

The forests in the center of the island are dark and dense.  

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