Pink Iguanas Missed by Darwin Are Discovered and Unexpectedly Rewrite the Evolutionary Genealogy of Galapagos Iguanas

HENRY FOUNTAIN of the New York Times writes that: “Charles Darwin was about as keen an observer of nature as ever walked the earth, but even he missed the pink iguana of the Galapagos. The rare land iguanas were first seen, in fact, only in 1986, when one was spotted by park rangers on Volcan Wolf on the island of Isabela. Since then they have been found only on that volcano, which would explain why Darwin missed them, since he didn’t explore it.” Researchers have determined “that the pink iguana is distinct from the two recognized species of land iguana on the Galápagos.” The species of pink iguana, have been determined by scientists to be genetically-distinct and represent a split from their green. Researchers have named the rare iguana after the Spanish word for pink—rosada. Alexis Madrigal, writing in the WIRED SCIENCE BLOG quotes scientists studying the new iguana who remark that “this form, which we recognize as a good species, is very important because it carries substantial evolutionary legacy," the authors of a new paper in the journal Proceedings of the National Academy of Sciences wrote. "Thus far the rosada form is the only evidence of deep diversification along the Galapagos land iguana lineage." Madrigal explains: “What” the researchers “found was surprising. Instead of being some slight variation on the Galapagos iguana theme, the pink lizards represent a distinct and early branch of the genetic tree. The genomic analysis of the species suggests a much deeper in history than most other Galapagos species, like Darwin's finches. In addition to the genetic differences, the pink iguanas also perform the characteristic mating ritual "head-bob" differently. Richard Black of the BBC elaborates on the differing movement of the head: “Iguanas typically bob and duck when they meet each other - a behaviour thought to be important for marking territory and courtship - and rosada does so in a more complex fashion than the yellow-coloured subcristatus or the other Galapagos species, Conolophus pallidus. It also has a different shape of crest. There is little sign of cross-breeding between pink and yellow. And the DNA analysis shows it is far more distinct from all the other land iguanas than they are from each other. That means the line that led to subcristatus and pallidus must have diverged from that leading to rosada long ago, with the split between subcristatus and pallidus coming much later. The DNA work puts the date of divergence between rosada and the rest at about 5.7 million years ago, raising a new set of questions,” explained Black."At 5.7 million years ago, all of the western islands of the archipelago did not exist," said Gabriele Gentile from the University of Rome Tor Vergata, who led the new analysis: "That's a conundrum, because it's now only inhabiting one part of Isabela that formed less than half a million years ago," he told BBC News. Black continues: “Even the oldest parts of the archipelago may be less than five million years old. The explanation may be that some volcanoes that are now under water were above it at the time when the first iguanas arrived, and this allowed some of the creatures to climb onto land and begin their separate evolution. Earlier DNA analysis suggests that land-based iguanas split from their marine counterparts about 10 million years ago.” Greg Laden adds: "The Galapagos are way over eight to ten million years old, and some time back around then were inhabited by iguanas from somewhere. Now keep in mind that the landscape looked pretty different back then. North and South America were not joined by the Panama land bridge, and there was probably a lot of movement of fauna and flora between what is now the eastern equatorial Pacific and the Caribbean. Land iguanas have always moved from island to island on a very low level in the Galapagos. Islands have slowly formed, grown large, then shrank, and slipped beneath the sea over time. But the temporal scale of island formation and disappearance is probably much slower than the temporal scale of iguana movement between islands. Furthermore, it is possible that inter-island movement becomes more likely when the islands become smaller, for ecological reasons." Unfortunately, Madrigal adds: “The iguana and other animals on Volcan Wolf are threatened by an "invasion of feral goats" that are devastating the area's natural flora. In the interest of preserving this genetic diversity, the biologists wrote that "a conservation program aimed at evaluating the risk of extinction of this newly recognized species," should be initiated. They estimate that the iguana could already by termed "critically endangered."