Column One: At last, Lonesome George can come out of his shell

BONK, BONK, bonk. That should be the libidinous sound of shell against shell but for Lonesome George, the last giant tortoise of his kind, there have been nearly 30 years of silent celibacy.

Lonesome George is the last remaining member of a subspecies that once lived on the most northerly island of Pinta in the Galapagos archipelago, where more than 150 years ago Charles Darwin was enthralled by the biggest tortoises in the world.

Attempts at finding a mate - organised by the tortoise dating agency based at the Charles Darwin Research Station on the island of Santa Cruz - have come to nothing. Lonesome just was not interested.

Now another team of scientists armed with the latest DNA technology think they know why. Lonesome's nearest genetic relatives live not on the nearby Isabela island but on the far-off islands of the southern Galapagos.

Just as DNA fingerprints can prove a match in a court of law, they can also prove a match among tortoises. Lonesome George, instead of being introduced to what he would judge to be the nubiles of the southern islands of Espanola and San Cristobal, has had to face a bunch of northern suitors to whom he could not relate.

For many years the giant tortoises of the Galapagos were plundered by passing buccaneers and pirates as a source of fresh meat. They can, after all, live up to six months without food in a ship's galley and still provide up to 200 pounds of edible flesh.

Within the Galapagos archipelago scientists have identified up to 15 separate subspecies or "races", although only 11 survive today. Six of these live on separate islands, with the rest inhabiting the slopes of the five volcanoes on the largest island, Isabela.

The most seriously endangered is the subspecies Geochelone nigra abingdonii, the

Abingdon Island tortoise, whose sole representative is Lonesome George.

Although the nearest buccaneers are now confined to Wall Street, the tortoises still face the ever-present threat of their young being eaten by newly introduced species, such as rats, dogs, and feral pigs.

The subspecies are identified by the differences in appearance of their shells, legs and necks. However, some subspecies are more difficult to distinguish than others, making genetic tests based on DNA a better alternative to physical differences between the races.

In the journal Proceedings of the National Academy of Sciences, Adalgisa Caccone and colleagues from Yale University have done that, which is how they found Lonesome George's nearest relatives on the most distant islands.

The reason for the apparent discrepancy comes down to the mode of transport used by the tortoises' ancestors in their original colonisation from the mainland of South America. The scientists say: "There is a strong current running northwest from the northern coast of San Cristobal, leading directly to the area around Pinta. These tortoises are not strong swimmers and thus their direction of rafting in the ocean must have depended largely on current."

Lonesome George may yet have one last chance of bonking his way to posterity.