Darwin's Tortoises More Diverse Than He Knew

Distribution of tortoise taxa on the Galapagos island of Santa Cruz. Credit: Yale

Unnamed taxon of Galapagos tortoise. Credit: Yale

The giant tortoises of the Galapagos Islands inspired Charles Darwin to formulate his theory of natural selection to describe the evolutionary diversity of species.

Now those tortoises have been found to be even more diverse than Darwin knew.

Nearly 150 years after Darwin's most important work, scientists have found the tortoise Geochelone nigra, found on the Galapagos island of Santa Cruz, is not one species but three.

The discovery, announced today, was led by Yale University scientists Michael Russello, Adalgisa Caccone and Jeffrey Powell and is reported in the Royal Society of London's journal Biology Letters.

Darwin and others identified the single taxon, or species, based on visible characteristics such as shell shape. The new research employed DNA analysis. Altogether there are 11 taxa of tortoise on the islands.

Between 2,000 and 4,000 individual tortoises remain on Santa Cruz, and there may be as few as 100 individuals in each of the new taxa, the scientists said in arguing for conservation of the habitat.

"It is ironic that while Santa Cruz has the largest population of tortoises, it also has the largest human population -- projected to double in the next eight years -- which is their greatest source of endangerment," Russello said. "Since accurate taxonomy is crucial for effective conservation policy, these results have fundamental importance for preserving the genetic and taxonomic diversity of these historically-significant reptiles."

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