How Does One Decide Whether A Distinctive Population Is A Different Species?
Anolis sagrei nelsoni. Photo by Steve Busack.
Bob Powell raises an important point in a recent comment, concluding “So, at what point does a differentiated isolate cease to be a subspecies and become a species?” In other words, how do we decide whether to recognize a distinctive population as a different species? I’m not talking about the situation where somebody goes out and comprehensively samples a clade and then uses the latest fancy-pants statistical wizardry to decide how to “delimit” taxa into one or multiple species. Rather, I’m going old school, focusing simply on the situation in which one has a population that is distinctive from other populations. Should we recognize that population as a different species? What kind of evidence is sufficient?
The context is the population discussed last week, Anolis sagrei nelsoni, from the remote Swan Islands 90 miles off the coast of Honduras. This isolated population is morphologically distinctive in many ways from other sagrei. It’s larger, has more lamellae on it’s toes, and, at least in the photograph above, has a very dark dewlap. Very likely, when Randy McCranie is done examining their scalation, he’ll document other peculiarities. Is this enough to decide to recognize Anolis nelsoni? Certainly, in recent years the same approach has been taken to recognize a number of other Central American anole populations as distinct species.
One problem with this approach is that nelsoni probably lies phylogenetically somewhere within what is currently recognized as A. sagrei (just my guess, but the only phylogeographic study on sagrei to date placed Belize populations in the middle of sagrei). Hence, raising nelsoni to species status would render the rest of sagrei paraphyletic, which bothers some people more than others.
Another option is to name the population (or in this case, retain the population) as a subspecies. I recently semi-seriously suggested to a collaborator that we name two subspecies for populations of a species found on two islands. He just laughed.
The answer, of course, is to conduct a detailed systematic study of the entire A. sagrei clade, using both molecular and morphological data. The problem is that this is a huge undertaking. Even Al Schwartz didn’t tackle variation in sagrei! So, it may be a while before this gets done. What do we do in the meantime? Is it A. sagrei nelsoni or A. nelsoni? Good question, Bob!
Update on Expedition to Swan Islands
While we’re on the topic of A. sagrei nelsoni, I thought I’d fill you in on the star-crossed trip to the Swans, announced with such hullabaloo last week. Here’s what happened. The team assembled in the coastal Honduran town of La Ceiba on December 3. Our pilot came by to say that all was in order and that he’d pick up us after breakfast the next morning. Dawn duly arrived, and just as I was polishing off my breakfast burrito, Randy comes in and says that the pilot has called and that there’s a problem with the paperwork that was discovered when he went in to file his flight plan, and that we’d be a little delayed.
Here’s what happened: the pilot had talked with the naval authorities in the capital, Tegucigalpa (the only occupants of the Swan Islands are a small Honduran naval garrison). They had okayed the trip out there and said so in an email. They said they would send a piece of paper to the pilot, but it never arrived. The pilot didn’t think anything of it, because he had the email documenting that everything was set.
Apparently not. No paper, no flight. Email immaterial. And thus the scrambling began. The naval authorities in Tegucigalpa wouldn’t answer their phone. December 4 came and went. Maybe tomorrow. Friends of friends were enlisted back in Tegus (as it is called, herpetologically enough) to call lawyers, police chiefs, military brass to bring pressure for the permit. December 5 dawned. Still no permit, nor any clear indication if and when it might materialize. At that point, I bailed. Having to return shortly to Cambridge for my teaching commitments, it didn’t make sense to hang around on the off-chance that I’d get maybe a day in the Swan Islands (much as it killed me to give up my chance to visit there). Instead I went to Utila, in quest of the two endemic anoles from that tiny island (more on that later).
Meanwhile, Randy, Alexis and Leo braved it out in La Ceiba (and did a little anolizing when they could). The last I heard was an email last night, saying that everything looked good for a 6 a.m. departure this morning. And today…nothing. So, I’m hoping the gang has arrived in the Swans (where there is no internet, or much of anything else) and is madly collecting data and observing endemics. We’ll hopefully have a report in a week or so when they return. Stay tuned.
2012-12-09 02:21:07
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