Originally published January 13, 2012 at 8:42 PM | Page modified January 13, 2012 at 8:42 PM
Giant 'extinct' tortoises may still roam a Galápagos island
Blood sampling on the largest Galápagos island has revealed that about 84 tortoises had at least one purebred parent from a supposedly extinct species.
Los Angeles Times
LOS ANGELES — A giant tortoise species believed to be extinct for more than 150 years may be alive and well, a genetic survey has revealed.
Blood sampling of more than 1,600 tortoises on the largest Galápagos island, Isabela, has revealed that about 84 had at least one purebred parent from the supposedly extinct species, which once lived at the other end of the archipelago.
Researchers hope they can find these tortoises in the flesh, breed them and then release them onto Floreana Island, their native home.
The study was published this week in the journal Current Biology.
The giant tortoise, among the largest living reptiles, is an icon of the Galápagos Islands. The creatures are believed to have arrived on the volcanic islands 2 million to 3 million years ago from the South American mainland.
Each species — some larger, with domed shells; and others smaller, with saddleback shells — was unique to a particular island or volcano. The diversity of tortoise species Charles Darwin saw during his 1835 visit to the Galápagos Islands partly inspired his theory of evolution.
"I never dreamed that islands, about 50 or 60 miles apart, and most of them in sight of each other, formed of precisely the same rocks, placed under a quite similar climate, rising to a nearly equal height, would have been differently tenanted," Darwin wrote in "The Voyage of the Beagle," published in 1839.
But within only a few years of Darwin's voyage, one of the tortoises — the saddleback Chelonoidis elephantopus, living on the southern Floreana Island — had vanished.
Whaling ships and pirates long had hunted the animals for food and oil; tortoises could be stowed in the hull for months — flipped on their backs so they couldn't escape — without receiving food or water.
And humans introduced other threats on the islands. Rats from ships preyed upon tortoise eggs; goats trampled them and devoured vegetation. All tortoise species in the Galápagos Islands suffered, but perhaps none more than Chelonoidis elephantopus. By 1850, it was gone.
However, scientists sampling a different species, Chelonoidis becki, made a surprising discovery in recent years. Within this population of tortoises native to Wolf Volcano on Isabela Island, a handful bore traces of Floreana tortoise DNA in their genomes. The Floreana tortoise apparently had made it to Isabela and mated.
Researchers decided to look more closely on Isabela.
They took blood samples from 1,669 tortoises living on Wolf Volcano — about one-fifth of the tortoise population there — and compared them to a database of tortoise DNA.
The analysis showed 84 tortoises had more than traces of C. elephantopus within them: One of their parents was purebred C. elephantopus.
Based on genetic analysis, the scientists estimate 38 C. elephantopus tortoises had parented these offspring on Wolf Volcano. And while many of those parents may not be alive today, some probably are. Thirty of the 84 hybrids were younger than 15 years old, and the creatures are believed to live for more than 100 years.
