For the first time in more than a century, scientists have identified a new species of Galápagos tortoise, the grand giants of the Pacific archipelago that helped inspire Darwin’s theory of evolution.
The discovery, reported Wednesday in the journal PLOS One, adds pieces to the puzzle of the Galápagos tortoise, a celebrated and embattled symbol of the unusual islands.
The newly identified species lives on Santa Cruz, an island in the archipelago’s center, but turns out to have less in common genetically with Santa Cruz’s main tortoise colony, and to be closer to a species of tortoise on other islands. While separate species are often considered incapable of breeding with each other, genetic evidence indicates that the two Santa Cruz species have mated, albeit not very often.
“Now the genetics has put some real evidence that says the simple explanations don’t hold, that some of the islands have tortoises that arrived at different times from different islands,” said Oliver Ryder, director of genetics at the San Diego Zoo’s Institute for Conservation Research, who was not involved in the new discovery. “The recognition of this separate evolutionary history I think will be very important.”
The new species lives in eastern Santa Cruz, in an arid, lava-laced lowland that has been called Cerro Fatal (Deadly Hill) ever since a park ranger had a bad fall on the harsh terrain, said Linda Cayot, science adviser for the Galápagos Conservancy and an author of the new study. There are about 250 Cerro Fatal tortoises, compared with about 2,000 tortoises in a moister, more elevated southwestern section of Santa Cruz, called La Reserva.
Cerro Fatal tortoises are smaller, with pointier plates on their shells, but these differences were merely considered variations on La Reserva tortoises, said Adalgisa Caccone, a senior research scientist at Yale and the study’s senior author.
But genetic analysis revealed that Cerro Fatal was not only its own species but also that although two tortoise types shared one island, “they are not each other’s sister species,” she said. Rather, the closest relatives are from San Cristóbal, the easternmost Galápagos island, she said. And Cerro Fatal tortoises evolved much more recently, less than half a million years ago; Reserva tortoises have existed for almost one and three-quarter million years.
Peter Paul van Dijk, a tortoise expert not involved in the research, said the results suggested that Cerro Fatal tortoises probably drifted to Santa Cruz during a “once-in-a-decade or once-in-a-century extreme weather event” like a hurricane or typhoon.
This is generally considered the 14th confirmed species of Galápagos tortoise, including two extinct ones: Santa Fe, which died off more than 150 years ago, and Pinta, whose last survivor, Lonesome George, died in 2012.
While most species are named after islands or British explorers, the new species, Chelonoidis donfaustoi, has a distinctly local namesake: “Don Fausto” — Fausto Llerena Sánchez, a 75-year-old park ranger who recently retired after 43 years of helping to save endangered tortoises.
“I asked, ‘Can I do this?’” Dr. Caccone said about the name. Yes, she was told. “There is only one Don Fausto in the Galápagos,” she said, adding “he is very shy and reserved, but he was very pleased, very touched, very honored.”
The genetic analysis compared Cerro Fatal DNA with DNA from all known species, along with a Cerro Fatal skull and partial carapace from museums, and the Reserva “type specimen” stored in London. Surprisingly, the Reserva specimen contained traces of Cerro Fatal DNA, indicating the two species “can interbreed, but they tend not to,” said Dr. Caccone, who speculated that people occasionally brought the two tortoise types together.
“I compare it to the European monarchy, who went in different directions but sometimes intermarried,” Dr. van Dijk said.
Scientists hope the new species designation will help them raise money to study Cerro Fatal tortoises and better protect their habitat.
“The next step is to do a big census and figure out what the threats are,” Dr. Cayot said. “We still don’t know a lot about them.”