After finding the descendants of a species of giant tortoises believed extinct from the Galapagos Islands for 150 years, Yale researchers are hoping to save the species.
In an expedition to Isabela Island led by Adalgisa Caccone GRD ’86, senior research scientist in ecology and evolutionary biology, the researchers found 84 tortoises whose genes show that one of their parents is a member of the supposedly extinct species, C. elephantopus. Published Jan. 9 in the journal “Current Biology,” the subsequent report stated that at least 38 purebred individuals of that species are still alive, and Caccone said she hopes to return to the Galapagos to find them.
“We can bring back a species from near extinction,” said Caccone. “If we can find these individuals in a larger expedition, we can return the species to its [original state] and reestablish the ecological equilibrium.”
Thirty of the turtle descendants were younger than 15 years old, and since giant tortoises often live over 100 years, this data suggests some parents are still alive. Carefully breeding the hybrids may also allow scientists to revive the C. elephantopus species even if the purebreds cannot be found, Caccone added.
The study claimed to be the first to rediscover a supposedly extinct species by analyzing the DNA of its offspring, though Caccone said in an interview with the News that her team simply applied standard analytical techniques.
“We had access to a large database that included the genetic fingerprints of [diverse giant tortoise] species, including extinct data,” Caccone said. “It was a huge effort, and a lot of undergraduates helped us with the project [to analyze all the samples].”
The team accumulated blood samples from over 1,600 tortoises, around 20 percent of the total tortoise population on Isabela Island, and compared the DNA to a genetic database of tortoise species. They found close correlations to the extinct species, identifying 84 direct descendants.
When Charles Darwin explored the islands in 1835, he found fifteen species of giant tortoises. Since only eleven species remain in the Galapagos today, Caccone said it is important to halt this rapid extinction. The differentiation Darwin saw between similar species on different islands, such as finches, was crucial in the development of his theory of evolution.
The giant tortoise is the only grazing herbivore native to the Galapagos, and plays an important ecological role, Caccone said, by helping to keep vegetative growth in check. On some islands where tortoise populations have dwindled, invasive plants and overgrowth have become a problem, she said.
On Floreana, the “extinct” species’ native island, the ecosystem is out of equilibrium. Caccone speculated that the tortoise was likely transported to Isabela aboard a ship as food, and then left on the island. Meanwhile the population on Floreana was wiped out due to hunting by whalers, pirates and local workers during the 19th Century.
University of British Columbia biology Professor Michael Russello, who contributed to the study, said he looks forward to a future expedition to the Galapagos that will allow conservationists to establish a breeding program and restore the species to Floreana.
“The return of tortoises to Floreana would [help] to restore the native flora and fauna of the island,” Russello said.
George Amato GRD ’94, director of the Sackler Institute for Comparative Genomics at the American Museum of Natural History, called the study “exciting” and “very significant.” He added that he is optimistic about the likelihood of finding the parents and hopeful about seeing the research translate into measurable conservation initiatives.
Even if purebred members of C. elephantopus cannot be found, Russello and Amato said the 84 offspring found may cumulatively have enough genetic variation to design a breeding program that would revive the species.
Ths project could provide a case study of how to restore extinct species from their close descendants.
“Success with this one species will give hope and a practical example for future conservation efforts, maintaining public interest in conservation that is essential for [receiving] funding and [influencing] political or community organizations,” said Brittney Kajdacsi ’11, a lab assistant to Caccone.
The giant tortoise is among the largest reptiles and longest-living animals on Earth, thought to have arrived on the Galapagos Islands from Ecuador about 1 million years ago.