A genetic study of giant tortoises on the Galapagos island of Santa Cruz reveals two different species and causes some head scratching amongst taxonomists

In 1902, American naturalist Rollo Beck stepped ashore on the Galapagos island of Santa Cruz. He’d been urged by his patron Walter Rothschild “to leave no stone unturned” in his efforts to collect giant tortoises from the island and “after a long and wearisome hunt,” he came up trumps. One of the seven specimens Beck collected became the type specimen for the tortoises on this island, now referred to as Chelonoidis porteri.

But just over a century later, in 2005, geneticists demonstrated that there appear to be two distinct species on the island. The two lineages live just 20 km apart yet the clear genetic differences indicate they have been heading in different evolutionary directions for at least 1.7 million years.

After a decade-long investigation, this division is now official, formalized in a paper published today in PLoS ONE. Where there was just one species yesterday (the Santa Cruz tortoise C. porteri), we can now recognise two (the Western Santa Cruz tortoise C. porteri and the Eastern Santa Cruz tortoise C. donfaustoi).



Facebook Twitter Pinterest The newly recognised species - Chelonoidis donfaustoi - is named after veteran Galapagos National Park ranger “Don Fausto” Llerena Photograph: Washington Tapia

I have written about this paper for New Scientist, but there is an interesting taxonomic footnote I want to focus on here. When Rothschild wrote up his original description of the Santa Cruz tortoise in 1903 and identified one of Beck’s tortoises as the type specimen, he did not specify which bit of the volcano it had come from.

The geneticists, when they studied ancient DNA obtained from the C. porteri type specimen, were in for a surprise. From their analysis of living animals, it’s clear that hybridization between the two populations can occur but has only done so very infrequently. Yet Beck appears to have collected a hybrid. “That took us back several months,” says Gisella Caccone, a geneticist at Yale University and the senior author on the paper.

Facebook Twitter Pinterest The type specimen of Chelonoidis porteri 1949.1.4.38 at the Natural History Museum in London Photograph: Adalgisa Caccone

Mercifully, the International Code of Zoological Nomenclature is clear on what should be done in this situation. The original name can still exist “even if it is found that the original description or name-bearing specimen(s) relates to more than one taxon,…or later found, to be of hybrid origin.”



Beck’s tortoise (1949.1.4.38) retains its privileged position as the type of C. porteri and remains, surrounded by other type tortoises, in the vertebrate store in the basement of the Natural History Museum in London.

Tale ends

Based on weight of numbers, the chances are that Rollo Beck collected 1949.1.4.38 from the western population (where there are more than 2000 tortoises today) rather than from the eastern population (where there are only around 200). Beck’s field notes from the Rothschild expedition could confirm this, but I have been unable to locate them. But we do know that when Beck returned to Santa Cruz as part of the California Academy of Sciences Galapagos expedition in 1905, he returned to the same spot as before on 25 October 1905 (see the diary of herpetologist Joseph Slevin). During this stop-off the catalogue of specimens shows they got several tortoises a few miles inland from “Puerta de la Aguada”. There is some uncertainty where this might be but if it’s anywhere near what is now Playa el Garrapatero, it would place them within the current range of the Eastern Santa Cruz tortoise rather than the Western Santa Cruz tortoise. Puerta de la Aguada anyone?



If there is a zoological specimen with a great story that you would like to see profiled, please contact Henry Nicholls @WayOfThePanda.