Science News

Giant tortoises not gone yet

This week saw the return of Galapagos Day, an annual event held by the Galapagos Conservation Trust and this year there was some good news: a species of giant tortoise that was thought to have gone extinct over a hundred years ago may in fact not be lost forever.

A team of scientists from Yale University in the States have extracted traces of DNA from specimens of extinct Galapagos tortoises kept in museums, and discovered that at a species that used to live on Floreana Island was genetically distinct from all the other giant tortoises.

The results of the study published in the PNAS journal this week by Giselle Ciccone and her colleagues might not be such ground breaking news, were it not for another discovery they made among tortoises still living in Galapagos – some of the close relatives of the extinct Floreana Island tortoises are still with us.

When Darwin visited the Galapagos Islands in 1835 he was inspired by the incredible giant tortoises which can grow to up to a quarter of a tonne and live for over a century. It wasn’t so much their great size that wowed him, but the fact each island seemed to have its own species of tortoise – the isolation of the islands meant that different tortoises evolved subtle differences from each other.

But sadly, their great size and lack of speed has meant that giant tortoises have suffered from human greediness, with four out of 15 species going extinct. The Floreana tortoises are thought to have gone extinct within 15 years of Darwin’s visit.

What Ciccone and her team have discovered is that some of the tortoises living on Isabela island are in fact a long lost relations of the extinct Floreana species – called Geochelone elaphantopus.

What probably happened is that somehow, a few Floreana tortoises found their way to Isabela, perhaps a whaling ship left them there realizing they had more food on board than they needed. And these visiting tortoises bred with the residents producing hybrids – now some of Isabela tortoises have half Floreana genes.

This means that even though there are no living Floreana tortoises, their genes do live on and there is potential that a careful breeding programme could restore them – one day perhaps – to their former glory. It would take an extremely long time, since giant tortoises take so long to breed but in theory, the living hybrid tortoises could be bred and selected so that they only possess the original floreana genes.

28th Sep 2008