Jan
14
2009

Elusive pink iguana eluded even Darwin

Conolophus rosada: Research scientist Gabriele Gentile holding the elusive pink iguana.
Conolophus rosada: Research scientist Gabriele Gentile holding the elusive pink iguana.Courtesy Photograph settings by Gabriele Gentile, photo shot by an assistant
A pink lizard that eluded Charles Darwin when he visited the Galapagos Islands nearly 175 years ago has been recognized as a new species of land iguana. Conolophus rosada is found only in the region of Volcan Wolf volcano on the island of Isabela.

"That Darwin might have missed this form is not surprising, because he stayed in the Galápagos only five weeks, and he did not visit Volcan Wolf [volcano], which to our knowledge is the only place on the archipelago where the pink form occurs," said lead researcher Gabriele Gentile of the University Tor Vergata in Rome, Italy. "What is surprising is that several other scientists visited in the last century Volcan Wolf and missed this form."

Two genera of iguana populate the Galapagos – land iguanas (Conolophus) and marine iguanas (Amblyrhynchus). The two branches split off from a common ancestor about 8-10 million years ago while still on the mainland. The pink iguana, which branched off the Colonophus line, can reach a length of more than 3 feet, and weigh up to 15 pounds. Park rangers first stumbled upon it in 1986 but not until now has it been recognized as a new, separate species.

Darwin spent only five weeks exploring the Galapagos when the HMS Beagle stopped at the archipelago to gather food for the voyage back to England. He investigated the island of Isabela but not around the Volcan Wolf volcano, the only area where rosada has been found. Overall, the naturalist wasn’t too impressed by the land iguanas he encountered on the Galapagos, He described them as “ugly animals, of a yellowish orange beneath, and of a brownish-red color above: from their low facial angle they have a singularly stupid appearance."

Good looks aside, the pink iguana presents other problems for modern scientists. Recent genetic analysis shows the rosada species diverged from other lines of land iguana about 5.7 million years ago. The trouble with that is the island of Isabela is only about one million years old and the oldest extant island in the chain, Espanola, is only 3-4 million years old. That means the split must have taken place somewhere else. But rosada hasn’t been found anywhere else in the Galapagos. How can this be?

One possibility is the split took place on the mainland before iguanas arrived on the islands, possibly floating there on rafts of vegetation. That would have been a long, miserable trip over 600 miles of open water. More likely rosada developed on an earlier island in the chain that no longer exists above sea level. Plate tectonics provide an explanation for this. Ocean crusts spread out from mid-ocean ridges located along the edges of plates moving away from each other. The Galapagos are part of the Nazca plate which is moving east-southeast (at about 7 cm/year) toward the continent of South America. The island chain was created (and is still being created) as the plate moved over a hotspot where a mantle plume is pushing up into the lithosphere and crust. Magma from the plume forms undersea volcanoes that build and sometimes break the ocean’s surface as islands. The Hawaiian Islands were created the same way but on a plate moving in a north-northwest direction.

As it moves toward the South American coastline, the heavier Nazca plate sinks beneath the lighter continental plate in a process called subduction. This means the earliest formed islands in the chain also sink and there is evidence of underwater seamounts between the archipelago and South America. Some of these have been dated to as much as 11 million years old, which means the pink iguanas could have split off from the land iguana line when older, earlier islands were still above sea level.

"This event is one of the oldest events of diversification among species in the Galápagos overall," Gentile said. "The Darwin finches are thought to have differentiated later than the split between the pink and yellow iguana lineages."

Despite rosada's evolutionary ranking, fewer than 100 pink iguanas are known to exist today and the species could be in danger of extinction.

It is, however, fitting that news of the pink iguana comes now. 2009 has been proclaimed the Year of Darwin marking the 200th anniversary of his birth and the 150th anniversary of the publication of his most famous work On the Origin of Species by Means of Natural Selection.

LINKS
Story on LiveScience
Year of Darwin info
Discovery.com story
Geology of the Galapagos Islands

Your Comments, Thoughts, Questions, Ideas

bryan kennedy's picture

Whit kind of evolutionary advantage do you get from being pink? I know that iguanas use the sun to cook the food in their stomach by basking on black rocks. I would think that this would be better if you were black and could soak up energy from the sun. It seems like being pink wouldn't be so great. Hmm, just some random musing.

posted on Wed, 01/14/2009 - 3:29pm
mdr's picture
mdr says:

The basking in the sun advantage probably wouldn't apply to green or yellow iguanas either. It could be the only advantage of being a pink iguana is in attracting other pink iguanas. Isn't that enough?

posted on Wed, 01/14/2009 - 5:59pm
Tiger134's picture
Tiger134 says:

Well.. didn't you say that it was found near a volcano? Maybe it's too hot and so they're lighter so as not to retain so much solar heat on top of the natural heat from the earth..

then again, I don't know much about colors and heat retention.. just that my tan sedan was much cooler (in temperature) than my black one.

posted on Fri, 01/16/2009 - 10:38am
bryan kennedy's picture

That's a pretty great supposition Tiger134, especially since Volcan Wolf is one of the Galapagos' most active volcano. I don't know if the ground would be consistently hotter near it though?

posted on Fri, 01/16/2009 - 11:37am
Tabby13kat's picture
Tabby13kat says:

Maybe the gound or flora near the volcano is a pinkish color due to the volcano or minerals, etc found in the area. I would think that because they are only found near the volcano that the pink color would have something to do with the landscape color around the volcano which would let them blend in better. Another clue is that they say this iguana is elusive which makes me think it blends in with the terrain very well. Unless the terrrain had similar colors, pink would stand out.

posted on Mon, 01/19/2009 - 9:25am
mdr's picture
mdr says:

I contacted lead researcher Gabriele Gentile and asked him why the pink iguana was pink and he wrote me back this reply:

Dear Mark,

The most honest answer to the question: "Why is the iguana pink?" is "We don't know, yet".

Of course we can make speculations, but they have to be considered as working hypotheses and must be demonstrated. It's seems that carotenoid pigments, which are supposed to give the bright yellow color to the other species of land iguanas in the Galapagos, might
not occur in the derma of the pink ones, although the molecule is of course present in their organism.

However, as I said, this is pure speculation.

ciao

Gabriele

posted on Tue, 01/20/2009 - 7:29pm
fatyyttys's picture
fatyyttys says:

thats ilegal to hold one you do know

posted on Sat, 05/05/2012 - 9:45pm

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