A newly discovered species of iguana that sits pretty in pink on the Galapagos Islands offers new insights into how the islands came to be such a famous hotspot of unique biological diversity.
As you may know, this year sees the 150th anniversary of the publication of Charles Darwin’s revolutionary book On the Origin of Species. When he visited the Galapagos Islands in 1835, Darwin was astounded by the abundance of unusual species living on the dozen volcanic outcrops that make up the archipelago, but he missed a rather strange iguana with colourful, pink skin.
In fact, surprisingly, no-one had noticed the rosada iguana living on the slopes of the Volcan Wolf on Isabela Island until Galapagos Park Rangers came across it in 1986, and now, genetic studies have revealed it not only to be a separate species, but the oldest species of land iguana, the ancestor of all the other land iguanas in the Galapagos Islands.
We know all this thanks to a study led by Gabrielle Gentile from the University of Rome Tor Vergata in Italy along with her colleagues from the Charles Darwin Foundation and the Galapagos National Park Service in the Galapagos Islands and the University of New Mexico. Their study is published this week in the journal the Proceedings of the National Academy of Sciences.
Other than their distinct pink skin, the rosada iguanas also behave differently compared to the two other land iguana species. When they meet, iguanas bob and duck their heads, either in courtship or to defend their territories, and rosada head-bobs are more complex and elaborate than the other iguanas. They also have a different shaped head crest.
These findings have also thrown up something of a conundrum. The DNA analysis provides an estimate that the Galapagos iguana family tree split in two around 5.7 million years ago – leading on one side to the pink iguanas and on the other side, to the two other species. Previously it was thought that the current pattern of diversity in land iguanas originated much more recently, less than 1.8 million years ago in the Pleistocene Epoch. So this study pushed back the divergence of land iguanas way back to a time when not all the Galapagos Islands had formed including the island that is the only modern day home of the pink iguanas.
The depressing side to this story is that there are thought to be less than 100 of these pink iguanas left in the Galapagos – human hunters and invasive species are largely to blame for that – and they really are important in terms of our understanding of how these species evolved, since they are an ancient relict that goes back further than any of the other land iguanas living in the islands. So it seems that an urgent conservation plan is needed if they we want to still see them around for much longer.