Giant Galapagos Tortoise Genes Tell Story of Prehistoric Volcanic Eruption

A major volcanic eruption about 100,000 years ago has been recorded in the genes of giant Galapagos tortoises whose ancestors survived the eruption, Yale researchers report in a recent issue of Science.

The researchers analyzed a tortoise population called G. n. vandenburghi, living on the slopes of the volcano Alcedo on Isabela, one of the Galapagos Islands. They found very low genetic variability compared to other tortoise populations on Isabela.

“This is surprising because Alcedo currently houses the largest population of tortoises in the Galapagos,” said first author Luciano Beheregaray, a Yale molecular ecologist in the Department of Ecology and Evolutionary Biology, currently based at the Macquarie University in Sydney, Australia.

Beheregaray said Alcedo’s ancient eruption covered the tortoise habitat with miles of hot pumice that likely disrupted wildlife, including the giant tortoises. The G. n. vandenburghi tortoises currently have little genetic diversity compared with the other tortoise populations.

“We analyzed DNA data from the tortoises that live around the volcano and found a clear signature of past population size contraction,” said Beheregaray. “Populations from parts of the island that were not affected by the explosive eruption do not show the same genetic signature.”

Beheregaray and his team used modern statistical methods that extract historical information from mitochondrial DNA sequences to estimate when the contraction occurred and as predicted, it was about 100,000 years ago.

“Our results emphasize the value of modern molecular population approaches in obtaining historical demographic information that cannot be discerned based on contemporary scenarios,” said Beheregaray.

Other authors on the study included Claudio Ciofi, Gisella Caccone and Jeffrey R. Powell of Yale; Dennis Geist of University of Idaho; and James P. Gibbs of State University of New York.

Citation: Science, Vol. 290, No. 14, October 8, 2003.

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