Galapagos Tortoises and the Evolution of Extinction
March 19, 2010 § 4 Comments
When you think of Galapagos, the first two thoughts that come to mind are Charles Darwin and giant tortoises. The giant tortoise is the iconic symbol of these islands. The name Galapagos come from a Spanish world for saddle – referring to the shell of these gentle giants. The national park uses an image of the giant tortoise as its logo. Whenever you see information about the Galapagos – you see pictures of the beloved giant tortoise.
The world’s largest tortoises, Galapagos Tortoises have a lengthy 150-year lifespan. Male tortoises are known to grow to be over 600 pounds. The archipelago was never attached to a continent and all the plants and animals, which arrived in the Galapagos, did so by either swimming, flying or floating. The journey across the ocean was too difficult for grazing mammals that dominate the grasslands of other parts of the world, and thus the slow moving tortoise reigned as king for thousands of years.
At the time of Charles Darwin’s visit in 1835, it was thought that 250,000 tortoises and 12 subspecies existed here. It was the comments regarding the tortoises from the local vice-governor, which first dismissed by Darwin, would later come to inspire him:
“I have not as yet noticed by far the most remarkable feature in the natural history of this archipelago; it is, that the different islands to a considerable extent are inhabited by a different set of beings. My attention was first called to this fact by the Vice-Governor, Mr. Lawson, declaring that the tortoises differed from the different islands, and that he could with certainty tell from which island any one was brought. I did not for some time pay sufficient attention to this statement, and I had already mingled together the collections from two of the islands. I never dreamed that islands, about fifty or sixty miles apart, and most of them in sight of each other, formed of precisely the same rocks, placed under a quite similar climate, rising to a nearly equal height, would have been differently tenanted; but we shall soon see that this is the case. It is the fate of most voyagers, no sooner to discover what is most interesting in any locality, than they are hurried from it; but I ought, perhaps, to be thankful that I obtained sufficient materials to establish this most remarkable fact in the distribution of organic beings.”
Darwin and his shipmates aboard Beagle viewed tortoises much in the same way as the pirates and whalers, tortoises were something to be exploited. The members of the Beagle harvested 30 tortoises from the islands, which they ate on their way home.
Over the past few centuries the systematic harvesting of tortoises for meat, oil, as well as the introduction of new species dwindled the population down some 90% from what it was in during Darwin’s visit. Both the Floreana and Pinta tortoises are noted as extinct and all of the remaining 10 species of Galapagos Tortoise are listed as endangered species.
In 1959, 100 years after the first publishing of Darwin’s On the Origin of Species the Galapagos Islands became as a national park. The park service together with the Darwin Foundation has made remarkable steps over the past 50 years towards the preservation, conservation and restoration of native species.
Perhaps the best example of their efforts is the story of the Espanola tortoise. At one time there were at least 3000 native tortoises on the island of Espanola. However Espanola is one of the flattest and most accessible of the islands, making it a favorite place for passing ships. As a result by 1965 there were just 14 remaining tortoises living on Espanola – 2 males and 12 females. The tortoises were transferred to the Charles Darwin Research Station on Santa Cruz. A third male was then discovered at the San Diego Zoo. In the 1970’s the tortoise-breeding program began. From the brink of extinction, of 15 tortoise the program has been a success and today nearly 1500 Espanola Tortoise have been repatriated to their native island.
With the success of the Espanola program stopping the extinction of other species proved to be more problematic. In 1971, Lonesome George was discovered on the Pinta. He has the unique distinction of being is noted as the last remaining of his species. George was relocated to the Darwin Station and scientists began work on the question how to keep the Pinta Tortoise from becoming extinct. Two females from Wolf Volcano on Isabela were placed in the pin with George. These females were selected as they were found to be the genetically closest relation to George and though any off spring produced would not pureblood – the species would some how continue.
For years George showed little or no interests in these females. But in 2008, the national park announced both of Geroge’s companions laid eggs. The world awaited news if the Pinta race had been saved. At the end of the year it was announced none of the eggs were viable and their search for how to save the species continued.
In 1994 a team of Yale Scientists began the Galapagos Tortoise Genetics Process. The group went to Isabela and took blood samples from 27 tortoises living high on the Wolf Volcano. Some 2000 tortoises are thought to live in and around Wolf. These tortoises are of significant interest, as tortoises here, resemble more than one subspecies. Normally each group of tortoise will either have a domed shaped shell (similar to the tortoises of Alcedo or other parts of Isabela) or a saddleback shaped shell (similar to Lonesome George) depending on the environment where they live. Yet near Wolf, tortoises can be found with both domed and saddleback shells.
Over the next decade the genetics team began collecting DNA samples from the tortoises in not only in Isabela, but also began samples from tortoises at the Darwin Station, around Galapagos, and tortoises held in captivity all over the world. On Pinta they found they took DNA samples from the remains of 15 tortoises and they cataloged the information to gain a better understanding of the species.
As they began to review their database, the impossible seemed to be possible. First they believe they have discovered a second pureblood Pinta tortoise. A Tortoise known as Tony, thought to be approximately 50 years of age is living at the Prague Zoo – from all current data Tony appears to be the same exact subspecies as George.
As they sifted through the DNA information they discovered the reason the Wolf tortoises appeared to resemble more than one subspecies. Isabela and the area near the Wolf Volcano was often the last stop for pirate ships in Galapagos. It appears that these ships collected tortoises on other islands during their stay only to discard them here. When testing the DNA samples, several of the tortoises living on Wolf were found to be first generation hybrid Pinta tortoises – tortoises born to mothers from Isabela and fathers from Pinta. This discovery meant that some of the tortoises living on Wolf were 50% the same genetic subspecies as Lonesome George. This information provided new hope that by further investigation a pureblood or half-blood female Pinta tortoise can be found – and the Pinta race can survive.
The genetic team seemed to have uncovered a miracle – still there were more surprises to realize. The research discovered descendants of the extinct Floreana Tortoise. The Floreana subspecies became extinct during the early 20th century due to human activities, and unlike Lonesome George no known examples were known to have survived. Yet, the DNA research uncovered 9 tortoises with high percentage of Floreana genome (up to 94%) and they believe 1 tortoise may even be pureblood. Of the tortoises identified of being from Floreana 6 are female and 3 are male all of which are currently residing at the breeding center in Santa Cruz.
Drawing from the success of the Espanola breeding program these new findings of the Genetics team, man may now be able to make up for some of their previous wrong doings. What was once extinct may not be extinct in the future. It’s all just a matter of time with the help of science and mother nature.