Eggs that may have been fertilized by George are likely to be rotten. Credit: Galapagos National Park

Lonesome George, the sole surviving giant tortoise from the Galapagos Island of Pinta, looks set to remain lonely for some time longer. Eggs laid by two females who share his enclosure do not appear to be fertile, says a spokesperson for the Galapagos National Park.

The females, who have shared George's enclosure at the Charles Darwin Research Station on the central island of Santa Cruz for almost 20 years, are of a different but closely related species. After decades of reproductive reticence, they stunned scientists during the summer by building nests and filling them with eggs for the first time (see 'Does fatherhood loom for Lonesome George?'). The hope was that they had mated with George and he was about to become a father.

Wardens managed to extract 16 eggs and install them in an artificial incubator, although three are thought to have deteriorated quickly and been out of the running early on. The remaining 13 eggs had been expected to hatch this week, but a recent inspection suggests this is unlikely to happen. Most of them have lost significant weight, says Freddy Villalva, a park warden working at the Fausto Llerena Centre for Reproduction and Captive Breeding of Giant Tortoises on Santa Cruz. One egg, which entered the incubator on 4 August at 127 g, now weighs just 82 g — a drop of some 35%.

Close, but no cigar?

Whilst the mass of tortoise eggs can go up or down during incubation, such extreme weight loss is not a good sign, says Tobias Uller, a zoologist at the University of Oxford, UK. "A water loss of 35% sounds extreme to me and suggests something is wrong, in particular since incubation conditions should be optimal in the lab," he says.

Justin Gerlach, scientific coordinator for the Nature Protection Trust of Seychelles, agrees. "A 10% change would not be surprising in a fertile egg," he says, but "35% may be too much to be viable." In addition to the weight loss, several of the eggs have fungus growing on their shell. This only happens if an egg is cracked and may indicate that the insides are rotting, says Gerlach.

The reason for this latest setback remains uncertain, although, going on George's past reproductive performance, the most likely explanation is that he did not mate with the females or, if he did, failed to transfer viable sperm.

In spite of the bad news, Villalva believes that 20% of the eggs may be healthy enough to hatch. Toni Darton, chief executive of the Galapagos Conservation Trust, also remains upbeat. "The worldwide excitement caused by the discovery of eggs in Lonesome George's enclosure showed just how important a conservation icon he is," she says. "We will just have to keep our fingers crossed over the coming weeks."