'Extinct' tortoise likely still exists, scientists say

Dozens of giant tortoises belonging to a species believed extinct for 150 years may be living in a remote part of the Galapagos Islands, scientists believe.

Researchers at Yale University came to the conclusion based on the "genetic footprints" of the long-lost species Chelonoidis elephantopus found in the DNA of their hybrid sons and daughters.

Their analysis was published Monday in the journal Current Biology.

"To our knowledge, this is the first report of the rediscovery of a species by way of tracking the genetic footprints left in the genomes of its hybrid offspring," said co-researcher Ryan Garrick, formerly of Yale University and currently a professor at the University of Mississipi. "These findings breathe new life into the conservation prospects for members of this flagship group."

The tortoises — which live for more than 100 years in the wild, weigh nearly 408 kilograms and grow to nearly two metres in length — are famous for inspiring Charles Darwin's ideas about evolution by natural selection.

The species was originally found only on Floreana Island and presumed extinct soon after Darwin's historic voyage to the Galapagos in 1835. The tortoises disappeared on Floreana because of hunting by whalers and workers at a heating oil factory established on the island.

In 2008, a team of Yale researchers took blood samples from more than 1,600 tortoises living on Volcano Wolf on the northern tip of Isabela Island — more than 300 kilometres from Floreana.

After comparing the samples to a genetic database of living and extinct tortoise species, they detected the genetic signatures of C. elephantopus in 84 Volcano Wolf tortoises, meaning one of their parents was a purebred member of the missing species.

In 30 cases, breeding had taken place in the last 15 years, and since the lifespan of tortoises can exceed 100 years, there is a high probability that many of the purebreds are still alive, researchers said.

"If we can find these individuals, we can restore them to their island of origin," where they would play a vital role in maintaining the ecological integrity of the area, said co-researcher Gisella Caccone of Yale University.

And even if purebred members of the species are never found, their direct descendants will be vital to its conservation, Garrick said.

"Hybridization is considered largely deleterious to biodiversity conservation," Garrick said. "But in this case, hybrids may provide opportunities to resuscitate an 'extinct' species through intensive targeted breeding efforts."

Researchers don't think the tortoises got to Volcano Wolf on their own, but were likely transported there from Floreana as food and then either thrown overboard by whalers or left on the shores of Isabela.