An iguana appetizer

January 16, 2010 • 1:07 am

by Greg Mayer

No, it’s not a reptilian hors d’oeuvre. It’s pictures of a Galapagos land iguana, Conolophus subcristatus, to whet your appetites for those Jerry will have when he gets back. I toured the Galapagos 20 years ago, and took loads of pictures, but they’re Kodachromes (which I haven’t scanned), so the pictures of our saurian friend below are from my colleague and fellow evolutionary biologist Joe Balsano, who visisted in 2007, and then kindly regaled my Darwin class with tales and pictures of his adventure. (More Galapagos reptile photos, at the Galapagos Conservancy, here.)

The Galapagos land iguana, Conolophus subcristatus (Joe Balsano).

The first link above for the Galapagos land iguana, from the Galapagos Conservation Trust (the UK companion to the US-based Galapagos Conservancy) is slightly out of date when it says there are two species of Galapagos land iguana: there are three. The common, or just Galapagos, land iguana, Conolophus subcristatus, is shown above. The Barrington land iguana, C. pallidus, occurs only on the island of Santa Fe (also known as Barrington). The two species differ fairly subtly in color and scalation (pallidus being less colorful, with a more distinctive crest of spines; see the original description by Edmund Heller here [go to Proceedings of the Washington Academy of Sciences in the left sidebar], and the classic paper by van Denburgh and Slevin on Galapagos iguanid lizards from the California Academy Expedition here [go to Proceedings-California Academy of Sciences 4th series in the left sidebar]). These subtle differences are the sort of differences between allopatric populations (i.e., populations inhabiting distinct, nonoverlapping, geographic areas) that can lead to long and inconclusive arguments as to whether the populations should be recognized as species, or subspecies, or not named at all. These arguments are a common, and not at all unexpected, issue when dealing with organisms living on islands. (The evolutionary process issues involved, although not the taxonomic issues, are dealt with comprehensively in Jerry’s and Allen Orr’s Speciation.) But the newly discovered species the pink land iguana of Volcan Wolf on Isla Isabela (Albemarle), Conolophus marthae, is not one of these wishy-washy, is-it or is-it-not-a-species, cases: it’s a new species, alright.

The pink land iguana, Conolophus marthae. From Gentile, G., et al. 2009. An overlooked pink species of land iguana in the Galápagos. Proceedings of the National Academy of Sciences 106:507-511.

It is amply distinct, both morphologically and genetically, from the other two species, including in coloration and form of the nuchal crest, as you can see from the pictures above. But, more importantly, it is also sympatric (i.e., living together in the same place) with the common land iguana. This is important because the truest test of species status is the test of sympatry: whether two forms interbreed when they co-occur in nature. In this case, the two species live together side by side, and reproductive isolating barriers, such as differences in male behavior (see the original species description by Gabriele Gentile and Howard Snell), keep them genetically isolated from one another. (Gentile and colleagues did find a single individual which showed evidence of some genetic mixing, but it is evidently insufficient to breakdown the genetic isolation of the forms.) This is a really remarkable and exciting discovery, given how many scientists, park rangers, and even just tourists, have traversed these islands. (I have been to Isabela, not far, at least as the crow flies, from where the new species was discovered.)

Although I think it’s fair to say that interested scientists have been delighted by the discovery of the pink land iguana, a number have been disturbed by what Gentile and Snell did, or rather didn’t do, in naming the species: they did not collect a specimen to document the species, but relied upon blood samples and photos. Usually, when a new species of animal is described, a particular specimen is designated the holotype, and preserved and deposited in the collection of a museum that will make the specimen available for study by other scientists. The specific identity of the holotype fixes the application of the name, and study of the holotype helps resolve any questions or confusions concerning the status or identity of the species, as well as contributing to further knowledge of the species’ biology. But if there is no holotypic specimen, then other scientists are unable to check the describer’s claims, or test their conclusions, or advance the study of the species in any way. Gentile and Snell were aware that what they were doing was problematic, and addressed the question in their paper. They even designated a particular iguana as the holotype, but left it in the wild, hoping that at some later time it might be retrieved using a radio tag they put in it. They did not collect it out of concern that loss of even a single individual might drive the species extinct.

Alain Dubois of the Museum nationale d’Histoire naturelle and Andre Nemesio of the Universidade Federal de Minas Gerais, Brazil, have led the criticism of Gentile and Snell, while acknowledging that there may be times when it is not wise to collect a specimen. See papers by them here, here, and here; Thomas Donegan of Fundacion Proaves supports what Gentile and Snell did. In the bad old days of systematic zoology, species were often named without holotypes, and this led to much confusion. Lately, there have been several species named for which holotypes have not been collected, for the same reasons advanced by Gentile and Snell, and this has led to much controversy; many of the key papers are cited in the woks of Dubois, Nemesio, and Donegan, or in works cited therein.

Some people might ask, what’s wrong with a photo? Well, I think it should be evident that there are many things you can’t determine from a photo, but perhaps a mention of the most famous species named on the basis of a photograph will make some of the problems clear: that species is the Loch Ness monster, Nessiteras rhombopteryx (abstract only without subscription). To put it only a bit too simply, specimens are what separate zoology from cryptozoology, science from pseudoscience. More on this in a later post.

13 thoughts on “An iguana appetizer

  1. Maybe it’s time the tradition of putting a corpse in a jar is put to rest. DNA samples and photographic information (pictures, video, etc.) are quite enough, and potentially much more permanent (you can’t digitize a corpse, like you can photos/videos and DNA sequences).

    The comparison to Nessie is off the mark – if we had blood samples and photos even of the quality in this post, that would be ample evidence for the critter. What we have, instead, are fakes and indistinct photographs, with no physical samples whatsoever.

  2. If I were you I’d buy a good scanner and get to work on your Kodachromes. I’ve just bought one and am scanning in slides from between 20 and 25 years ago. Some are still in quite good condition and are rescuable with a little bit of photoshopping, but others have faded quite noticeably.

    1. Stephen – if slides from 20 years ago are fading, they are most likely not Kodachrome. That’s not a generic name for “color slide”, it’s a specific Kodak color film technology that’s incredibly sharp, very fade-resistant, and with some of the most realistic pleasing color of any film. You’ll find Kodachrome slides taken 50 years ago that are saturated, sharp, and gorgeous. It’s actually a black and white film to which dyes are added in the chemical processing, which makes the image sharper and the color-retention far superior to other color film processes.

      The slides that fade use the E-6 color film process (found in Ektachrome and most other film companies’ color slide films). It was never as good as Kodachrome, but it was cheaper and easier to process. Trouble is, the dyes fade fairly rapidly.

      Yeah, I’m a former photographer with a geeky romance for film technology, and I literally cried when Kodak stopped producing Kodachrome recently. When digital overtook most photography, it felt to me like a grand romance that failed – just couldn’t muster the love for pixels.

      Matt – please, please get some good quality scans of your Kodachromes and post them! And if they’re not Kodachrome but E-6 slides, Stephen’s right – scan them before they fade away (but please keep them in archival sleeves and out of sunlight – don’t throw them away like so many glib “I’m all digital now” people have).


      1. Well, you’re largely right of course. Yes, it’s mainly my Ektachromes and Agfachromes that are deteriorating, but some of the actual Kodachromes are also not quite what they were. (My finances didnt permit me to use exclusively Kodachrome.)

        What has surprised me is the amount of variation, sometimes even within a single film. I’ve found one film (Agfa) where most of the slides were not too bad, but a group of three, kept in the same box as the others, had faded almost to oblivion.

  3. I wonder what Dr. Coyne would have to say about the case of sympatric speciation. I remember his definition, at least the one he gave at Darwin/Chicago 2009, was that there would have to be free gene flow during the beginnings of speciation to be truly sympatric.

    1. Jerry has had a lot to say about sympatric speciation (see his book with Allen Orr linked to in the post), and will have more to say, I’m sure, in the future. There is no suggestion in the data on the land iguanas that the pink iguana arose by sympatric speciation from the common land iguana. The pink iguana’s divergence precedes the geographic differentiation of the various populations of the common land iguana. The Barrington land iguana arose by differentiation in allopatry, as indicated by its being nested within the clade of common land iguanas.


  4. It might be better use of your time to get a professional to scan your slides – faster, possibly cheaper and likely better quality.

    The first iguana is lovely – I like his smile and he really knows how to pose in the second photo. The pink one is fabulous *jazzhands*, though.

    I understand the problem, but I’m glad the poor critter was left in the wild. I recall a recent case where the holotype of an extinct species is not actually the fossil itself, because it’s enclosed in opaque amber, but a larger-than-life cast of the tomographic reconstruction (done at a synchrotron). I guess one way to deal with rare species in future is to use CAT/NMR-scans – once they get around to build machines that can be dragged to the Galapagos.

    1. The holotype can never be a representation of an animal, but is always the animal itself. This is a rule of the International Rules of Zoological Nomenclature, and a good one. I’m not familiar with the case you mention, but the holotype would be the animal encased in the amber. The tomographic reconstruction may provide very useful data about the holotype, but is not the holotype. The Tyrannosaurus rex at the Field Museum known as Sue has had her skull studied intensively by such methods (because they don’t want to break apart her skull), but the images produced are, of course, not Sue, but representations of her. Sue is not a holotype (because no one thinks she belongs to a previously undescribed species), but the same distinction applies.


  5. [this is addressed to Dubois and Nemesio]
    What the hell where they supposed to do, kill one? that’s pretty crazy. “oh look, a new species, unknown to science! let’s kill one hyuk hyuk!”

    come on, give me a break. Soon enough we’ll get a nice corpse, dead from natural causes – that can be your precious holotype.

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