Rediscovery of ‘Extinct’ Giant Tortoises in the Galapagos Islands

Posted by Maia Wikler in Galapagos News 19 May 2016
Giant tortoises in the breeding program. Photo © Joe Flanagan

Giant tortoises in the breeding program. Photo © Joe Flanagan

The Galápagos Islands, famed for the adaptive wonders of its unique species, had humble beginnings with just 15 original species evolving to make the islands their home after volcanic eruptions. The archipelago provided an ideal environment for the impressively adaptive tortoises to thrive in.

While you might think a volcanic eruption would gravely challenge the tortoise, they actually thrived. Scientists have found that once a volcano emerges it can create evolutionary shifts with enhanced conditions for gene flow. How does this happen? Volcanic eruptions can create land bridges between isolated volcanoes which allow for genetic variation as spatial and dispersal migration patterns shift. The Galápagos tortoises responded to the volcanic eruptions with quick changes, known as “rapid allopatric radiation.” In other words, this species represents one of nature’s greatest phenomenons in evolution. A study from the Proceedings of the National Academy of Sciences sums it up quite nicely, “Giant Galápagos tortoises are the largest terrestrial chelonians in the world and represent the only surviving group of giant tortoises where evolutionary divergence is evident among populations.”

Despite the adaptive resilience of the Galápagos tortoise, the onslaught of colonization in the late 1800s introduced poachers and invasive species to the islands. Ultimately leading to the demise some of the tortoise species. The powerful impacts of colonization are evident with the species of tortoise found only on Floreana Island as they became extinct just 15 years after Darwin’s visit in 1835. Recently, the tortoise species found exclusively on Pinta Island went extinct in 2012.

A genetic research program from Yale University began to pursue the seemingly impossible by launching an expedition to seek out any remaining DNA from the two extinct species. After years in the field and hundreds of tortoise tagged, researchers discovered 89 had DNA from the Floreana Island species and 17 had DNA from the Pinta Island species. The hybrid tortoise discovered on the expedition still maintain the distinctive saddleback shell found from Floreana and Pinta.

The tale of the scientific expedition is one for the books. Any tortoise found with a high proportion of ancestral lineage from Floreana or Pinta would be airlifted a makeshift lab on their ship. In total, 32 evolutionary wonders were airlifted to the ship and sent to a breeding facility in the Galapagos National Park. The purpose of sending them to the breeding facility is to restore as much DNA as possible originally found on the two islands. If this effort is successful, it will be key for the restoration of the island ecosystems. Adding the tortoises collected by researchers to the breeding program will also boost the genetic diversity for the species.

Hopefully, this discovery will result in a similar success story to the Española giant tortoises. In the 1960s, the population of Española tortoises had dwindled to a mere 15 individuals. Scientists brought the remaining tortoises to a breeding program to begin an effort to save the species. After 40 years, 2,000 Española tortoises have returned to their home on Española Island.  Now, their population is considered stable.

The careful work of biologists to recover species on the brink of extinction is an exciting accomplishment.  However, there is more work to be done to ensure the habitat of the tortoise population can maintain its ecological resources to support the restored populations.

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This post is by About Galapagos contributor Maia Wikler, a Colorado College graduate with a passion for anthropology, human rights, travel and conservation. When she isn’t writing or reading she loves to be active outside and planning the next adventure.

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