Chelonoidis elephantopus, a type of giant Galapagos tortoise that was thought to have become extinct over 150 years ago has been “found” in the genome of a similar species that currently lives in the Galapagos Islands.
First recorded in 1853 by Charles Darwin in his famous voyage of The Beagle, Chelonoidis elephantopus was never again seen by visitors or scientists in the Galapagos Islands. This species was believed to have been wiped out by the mid 1800’s by pirates and whalers who used these animals as a valuable source of food on their ships due to their tolerance of extreme conditions. A Galapagos tortoise can survive without food or water for up to a year, thus they were a highly prized food source by pirates and whalers who kept them alive on their ships without giving them any care. Giant Galapagos tortoises can reach almost 6 ft (1.8m) in length and weigh almost 900 lbs (408 kg).
Chelonoidis elephantopus was originally from Floreana Island, the second southernmost island in the Galapagos archipelago and the most frequented by pirates and whalers in the 1800’s. However, a study of the genome of over 1600 tortoises on Isabela Island (the largest island of the Galapagos Islands land formations and found 200 miles northwest of Floreana Island) revealed the presence of the DNA of Chelonoidis elephantopus on its very close relative, Chelonoidis becki.
The two species of Galapagos giant tortoises have shells of a different shape. The shells of C. becki are domed-shaped, whereas the shells of C. elephantopus on Floreana Island were saddle-shaped. Because in 2008 several members of C. becki were observed to have more saddle-shaped shells than dome-shaped, an investigation began to determine the cause of the difference in shell shapes. A DNA examination of these saddle-shaped variations revealed that they had to have had at least one parent which was a member of C. elephantopus.
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The final study showed that their genes were significantly different from those of other Galapagos tortoises on the Island and although the issue is complicated (and scientists estimate that at least 38 tortoises in their study could be purebred members of C. elephantopus), the conclusion is that the species is not extinct. Thirty of the tortoises whose DNA contained DNA from C. elephantopus were found to be less than 15 years old. Given that the average lifespan of a Galapagos tortoise is 100 years, researchers say that there is a strong chance that their C. elephantopus parent is still alive on Isabela Island.
Additionally, since scientific findings suggest there may indeed be a few dozen descendants of this Galapagos Island breed still roaming the island, researchers are anxious to locate this group. The task now is to establish a realistic plan to discover their territory and catch these “hybrid tortoises” and incorporate them into the current breeding program or design a new one. This will involve an enormous effort as researchers look in plain sight among other tortoise herds and search for a population that has established its own secluded territory. This is an exciting opportunity for conservationist to learn more about C. elephantopus and possibly discover additional hybrid offspring.
To make matters more interesting, researchers are not sure how C. elephantopus tortoises ended up on Isabela Island, almost 200 miles away from Floreana. As opposed to sea turtles in the Galapagos Islands area, Galapagos tortoises are not good swimmers. Some scientists have posited that these tortoises originally arrived via the Humboldt Current from mainland South America. Based on this premise, there is the possibility that the population or even a single pregnant female “migrated” to Isabela Island as a passive passenger via prevailing currents. The generally accepted best guess is that pirates and whalers hauled them from one island to the other, or that they threw some overboard when passing close to Isabela Island.
A detailed recount of these findings is published in the journal Current Biology. http://www.cell.com/current-biology/