'Pink' iguana product of ancient divergence, scientists say

Pink iguanas found near a volcano on the Galapagos islands and unknown to naturalist Charles Darwin during his visits to the region are a distinct species that diverged from other land iguana populations some five million years ago, scientists said Monday.

The findings are the first to describe the extremely rare pink, black-striped land iguanas, which escaped the notice of scientists until Galapagos National Park rangers spotted them in 1986.

The land iguanas, called rosada("pink" in Spanish), live near the northernmost volcano of the island of Isabela, one of the few places in theGalapagos thatDarwin did not visit during histrip in 1835.

Darwin's trip to the remote islands informed his research into the process of natural selection, a theory that became the backbone of modern evolutionarybiology. It also made the Galapagos region off the Pacific coast of South America a hotbed for research into evolutionary history, as many species, including some species of iguana, are found only on the islands.

"Despite the attention given to them, the Galapagos have not yet finished offering evolutionary novelties," said researcher Gabriele Gentile of the University Tor Vergata in Rome, who led the study.

That the pink iguanas are a unique species is interesting given their rarity, but even more surprising from the analysis of their mitochondrial DNA is how far their lineage can be traced back, said Gentile.

The researchers trace the divergence of the rosada species from other land iguanas back some five million years, to a period when some of the islands had yet to form.

As the volcano the iguanas live near is relatively young at only 350,000 years old, it means the reptiles must have existed elsewhere on the islands before, said Gentile. It also marks one of the oldest divergences ever recorded on the islands, he said.

The iguanas grow longer than a metre and up to 12 kilograms in weight. In addition to their distinct colouring, the rosada species also has flat dorsal head scales and strong differences in the pattern of its head-bobbing or nodding, a behaviour important to courtship and staking territory.

Because the pink iguana "carries a substantial evolutionary legacy," Gentile and his co-authors recommended the establishment of a conservation program to evaluate the risk of extinction to the species.

The findings were published Monday in the journal Proceedings of the National Academy of Sciences.