Bringing Back the Dead: Reviving an Extinct Tortoise Species
During the first half of the 19th century, more than 200,000 tortoises were hunted and eaten by whalers passing through the Galapagos Islands. The whalers rode the ocean currents into the southern corner of the archipelago, past the island of Floreana, where they would pick up tortoises for one main reason: they were a tasty source of food that had a difficult time running away. When time came to leave the Galapagos, the whalers would toss any tortoises that remained on the ship into the water to make room for the more lucrative whale blubber. These Floreana tortoises would swim to the nearest land, the northern Vólcan Wolf (V. Wolf) region of Isabela Island, and interbreed with the native tortoises.
Genetic analysis of tortoises living near V. Wolf and museum specimens of tortoises from Floreana Island has shown that the tortoises of V. Wolf have some genetic markers from the native population of V. Wolf and the extinct tortoise species native to Floreana Island, Chelonoidis elephantopus. The genetic analyses target single nucleotide polymorphisms (SNPs) that vary among the different species of tortoises scattered throughout the Galapagos Islands.
For the past fifteen years, Dr. Adalgisa Caccone, a senior researcher in the Department of Ecology and Evolutionary Biology, along with other scientists from Yale and numerous other institutions, has been working on the evolutionary genetics of these tortoises. The discovery of extant individuals that live on V. Wolf and carry genes from Floreana Island’s extinct species provides the opportunity to start a selective breeding program that can bring back the extinct species in approximately four generations of breeding—about 100 years.
“Genetic diversity is necessary for populations to survive disease and other disasters,” said Caccone. “It is a good measure of the capacity of a population to evolve and thus survive if environmental conditions change.”
According to Dr. Caccone, the project is relatively inexpensive and quite similar to the process of breeding cows to produce more milk. Tortoises are selectively chosen and bred to produce offspring that have the greatest chance of possessing the genetic markers from the extinct Floreana species. While it is nearly impossible to perfectly recreate the extinct species, this project would yield tortoises that have approximately 90% of the genetic markers of the Floreana species, effectively reintroducing the species with some of its original genetic diversity.
On average, Caccone travels to the Galapagos Islands—a four day trip from the United States—once a year to supervise the implementation of the project and to collect data, such as tortoise blood samples. A researcher could spend two weeks at the Charles Darwin Research Station on the island of Santa Cruz before returning home. If, however, data needs to be collected on other islands, such as at V. Wolf on Isabela Island, the typical trip will last about a month.
This project implements a methodology applied by farmers for centuries in order to remedy a significant problem: the growing list of endangered species. Although the project will take at least a century to complete, it has applications that are perhaps broader than we can imagine. The reintroduction of the extinct C. elephantopus will be a landmark step in the conservation movement. According to Caccone, since we have the means to help, it is our duty to preserve nature and its diversity.
Poulakakis N, et al. (2008) Historical DNA analysis reveals living descendants of an extinct species of Galápagos tortoise. Proc Natl Acad Sci USA 105:15464–15469.
Russello MA, Poulakakis N, Gibbs JP, Tapia W, Benavides E, et al. (2010) DNA from the Past Informs Ex Situ Conservation for the Future: An “Extinct” Species of Galápagos Tortoise Identified in Captivity. PLoS ONE 5(1): e8683.