The 2015 Expedition to Wolf: The Genetics

December 28, 2015

By Gisella Caccone, evolutionary biologist at Yale University

Tortoises arriving by helicopterWhen I saw the first tortoise being airlifted in its green net, from his home on the western flanks of Wolf Volcano, and then gently deposited on the deck of the Sierra Negra, I was suddenly brought back to a beautiful fall afternoon in 2001 at Yale. I was looking at DNA sequences of a group of tortoises from Wolf that should belong to a single species, Chelonoidis becki. I did the lab work back then so I was the first to see the data “fresh off the press.” I vividly recall my surprise when I realized that something unexpected was happening. Among the 60 tortoises sampled on Wolf Volcano, some had DNA sequences that were clearly distinct — so divergent that I remember saying aloud: “Where are they coming from, Mars? They look like aliens!” We had an extensive reference database that included all known living populations of giant Galapagos tortoises, but these aliens matched none!

We solved the mystery in 2005, when we began analyzing DNA from bones of extinct species of giant tortoises. These “aliens” from Wolf carried genetic material from two recently extinct species, one from the island of Pinta (C. abingdonii, officially extinct with the death of Lonesome George in 2012) and the other from Floreana Island (C. elephantopus, extinct about 150 years ago). They were not from Mars after all, but from the recent past.

But how did they get to Wolf Volcano, a remote location not in the path of natural migrations of tortoises due to ocean currents among islands? Humans likely played a big role in their diaspora. A favorite source of fresh meat, whalers and pirates collected tortoises by the hundreds. Their logbooks document incidents of tossing tortoises overboard to lighten the load during fights or when fleeing. These animals landed on the western flanks of Wolf and interbred with the local species. Meanwhile, back on their islands of origin, their relatives went extinct. Ironically while human activities led to their extinction on their original islands, human activities also resulted in the preservation of their genomes, locked in animals with mixed genetic material.

Tortoises arriving by helicopterOnce we realized the DNA of extinct species could be mined from living individuals, we started planning an expedition to see how many animals with mixed ancestry we could find. In 2008 we returned to Wolf and took blood samples from 1,667 tortoises. Subsequent genetic analyses identified 17 with genetic material from the extinct Pinta species and over 80 with genetic material from the extinct Floreana species. This led to the proposition that it might just be possible to bring the tortoises from Pinta and Floreana back from extinction through selective breeding.

There I was on a misty afternoon on the deck of the Sierra Negra, watching the next phase of this long story unravel. The helicopter gently deposited the first animal on the deck and I welcomed this saddleback female thinking back to that fall afternoon in New Haven, when I first gleaned the DNA data of her relatives. Seeing an animal that had been part of my thoughts for so many years was exciting, and somewhat overwhelming. I am so grateful to have been part of this incredible adventure. The power of genetic analyses and especially the importance of long-term studies, such as ours, have never been more real. It took more than 20 years to put together the necessary database! And we could never have realized that DNA from extinct species was still present in living relatives without the availability of museum specimens, which allowed genetic fingerprinting of the two extinct species. This project is one of the clearest testaments to the importance of museum collections in conservation.

A tortoise on the deck of the Sierra Negra

What’s next? We will genetically analyze the blood samples of the 32 animals we brought back to the Galapagos National Park tortoise center on Santa Cruz to then design an optimal strategy to recover animals as close to the “pure” extinct species as possible. During the expedition, we also collected blood from another 148 saddleback tortoises that could potentially also be used, but due to space limitations we left the giants on the island, tagged with microchips. Next year, we can go back and retrieve them, if necessary. They will wait for us; after all one year in a tortoise’s life is little more than a blink!

Although we will never have a pure C. abingdonii or C. elephantopus roaming the lava slopes on Pinta and Floreana, as we cannot turn back time, we will try our best to produce animals close to it — to partly amend what we humans did to them and to their island ecosystems, which need their major herbivore. I am very honored to be part of this effort and humbled by the scope and magnitude of the project, the first of its kind.

Tortoises on the Sierra Negra

A blog provides a unique opportunity to recognize the contributions of many people and organizations. I want to thank Jeff Powell, my husband, who put me on the “tortoise path” after getting energized and intrigued by their story during a trip sponsored by the Yale Alumni Association, where he connected with Linda Cayot. He led the Yale team for many years. I would not have been on the deck of the Sierra Negra if not for his foresight. Neither of us is a herpetologist, but we fell in love with the tortoises, the islands, and felt that we, as evolutionary biologists, needed to pitch in. I wish Jeff and Linda could have been with us on that deck.

I was very lucky to have had the help of many students and postdocs. James Gibbs was the first postdoc and we have continued this journey together since the onset. Four other postdocs from Yale were with us on Wolf Volcano, pictured below. Genetic work is expensive and we have relied on the support of many organizations. A special thanks is due the Galapagos National Park Directorate and Galapagos Conservancy for creating the Giant Tortoise Restoration Initiative, a powerful vehicle to focus all efforts to restore the giant tortoises to their islands of origin. They put their trust in us when, especially at the beginning, there was no reason to know if what we found would ever lead to anything practical.

Yale team on Wolf Expedition


Gisella CacconeGisella Caccone is an evolutionary biologist at Yale University, where she is a Senior Research Scientist and director of the Center for Molecular Systematics and Conservation of the Yale Institute for Biospheric Studies. She has a BS from the University of “La Sapienza” (Rome, Italy) and a PhD in Biology from Yale University. Gisella has been studying the genetics of Galapagos giant tortoises since 1994 and has led the tortoise genetics team for the last decade.


This is Part 2 of a six-part blog series from various participants of the expedition documenting the events of the 2015 expedition to Wolf Volcano. Read Part 1: Overview by Wacho Tapia and Part 3: A Pinta Perspective by Elizabeth Hunter.


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  1. thank you for your fine work, and for writing this lucid and hope-filled article. The possibilities for conservation are extraordinary!

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