Category: Notes from the Field Page 8 of 22

The Grenadines. (http://en.wikipedia.org/wiki/File:Grenadines- Archipelago)

Check out the Grenadines, a polyphyletic chain of approximately 600 islands found at the southern end of the Lesser Antilles. The islands north of the Martinique Channel are governed by St. Vincent. The islands south of the Martinique Channel are governed by Grenada. (Grenada, you’ll recall, was invaded by the US in 1983).

Given Martinique Channel’s apparent role as a political boundary, I wondered if it is also an important biogeographical boundary, much like Wallace’s Line in Indonesia. Wallace’s line, which passes through through the Lombok Strait between Bali and Lombok and between Borneo and Sulawesi, denotes a clear faunal break between Asian and Oceanic faunas. The biogeographical explanation is that Wallace’s line follows the transition from continental shelf to deep water channel, which serves as a barrier for migration.

Martinique Channel (line added).

A look at the Caribherp distribution of herpetofauna found on the Grenadines suggests that the Martinique Channel is not actually a biogeographic break. The distribution of most herps found on the Grenadines crosses the channel, suggesting that the channel is not a barrier to migration. And, consistent with this, Google Earth suggests that the channel is not very deep.

Oh, almost forgot: the Anolis species on the Grenadines are A. aeneus, A. richardi, and the invasive A. sagrei.

Anolis aeneus. Photo from http://www.kingsnake.com/westindian/anolisaeneus5.JPG.

Anolis richardi. (Photo from http://reptile-database.reptarium.cz)

Rick Stanley photo #2 of a large Costa Rican anole

Award-winning nature photographer, naturalist, and undergraduate Rick Stanley spied this large anole in Costa Rica. Is it A. microtus? A. insignis? Something else?

Photo #1

Here’s what Rick had to say: “I encountered these impressive lizards on the Pacific Slope of the Cordillera Talamanca, on the border of Chirripo National Park, in the summer (wet season). They were between 1500 and 1600m elevation, in secondary forest habitat. Although sightings were about a month apart, all of the animals observed were in the same general area near the cabins.

Photo #3

Images 2/3 are of the same individual. Image 1 was taken nearby at an earlier date, so it could be the same individual as well. Image 4 is of a different, slightly smaller individual seen along with 2/3 (perhaps the female?). The male(?) displayed his dewlap at me- I think it was an aggressive gesture, because the female was out of sight by then. When I first saw him, he had a large clump of moss in his mouth that he proceeded to devour (chances are there was an insect in there as well).

Photo #4

The lizards were over a foot long including the tail, although I didn’t catch them and measure svl. The first time I sighted 1 it was sunning. Later, it changed color and appeared more like the individual in photos 2 and 3. Didn’t move much, as I found him in the same place the next day, hanging head down on some vines.

There is also some damage to the animal’s dewlap that isn’t part of the pattern.”

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?

Read More

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!