Jan 10

A species of Galapagos giant tortoise believed extinct for over 150 years may still be alive, according to scientists.

Photo of Volcan Alcedo tortoise walking

A Volcan Alcedo tortoise (Chelonoidis vandenburghi), a relative of the ‘extinct’ giant tortoise from Floreana

The species, Chelonoidis elephantopus, was once found on the island of Floreana in the Galapagos, but was hunted to extinction by whalers who visited the Galapagos Islands during the 19th century.

However, a team of scientists from Yale University have now discovered hybrid tortoises which appear to have the ‘extinct’ species as one of their parents. The hybrids were found among a population of Volcan Wolf tortoises (Chelonoidis becki) living at the northern end of the island of Isabela, another of the Galapagos Islands.

Pure-bred individuals may still exist

After the hybrid tortoises were found, the team originally speculated that by careful cross-breeding over many generations, it might be possible to re-create the extinct giant tortoise species.

Photo of several Volcan Alcedo tortoise pairs mating in shallow pool

Volcan Alcedo tortoises mating

However, further expeditions to Isabela have found a number of individuals that appear, from a study of their genes, to have pure-bred C. elephantopus as one of their immediate parents. As some of the hybrids are only 15 years old, this suggests that their pure-bred parents may still be alive, particularly given that giant tortoises can live for over 100 years.

Unique island inhabitants

Giant tortoises are endemic to the Galapagos Islands, where they are likely to have originally arrived by floating from the shores of South America.

Photo of old male Duncan Island tortoise in typical habitat

Duncan Island tortoise (Chelonoidis duncanensis) reaching for food. The distinctive ‘saddleback’ shell of some Galapagos giant tortoises enables them to reach taller vegetation.

The distinct appearance and variety of shell shapes shown by giant tortoises on different islands helped inspire Charles Darwin’s theory of evolution – as populations on the different islands were relatively isolated from one another, they evolved in slightly different directions as they adapted to different conditions.

For example, C. elephantopus of Floreana Island has a distinctive saddleback-shaped shell, while species from neighbouring islands have a more dome-shaped shell.

Captive breeding

The scientists believe that the tortoises from Floreana Island were most likely transported to Isabela on whaling ships, and subsequently became established on the island.

Photo of young James Island tortoises at Charles Darwin research station

Young James Island tortoises (Chelonoidis darwini) at Charles Darwin Research Station. Captive breeding may be essential in ‘resurrecting’ the giant tortoises of Floreana Island.

Despite being the largest living tortoise species, giant tortoises can be surprisingly difficult to locate.

According to Dr Gisella Caccone, one of the scientists, “The landscape on Volcano Wolf is hard, the vegetation thick with lots of bushes and nooks, and the carapaces are translucent so you need a trained eye to see the shininess of the shell.”

However, if the suspected pure-bred individuals can be found, they could potentially form the basis of a captive breeding programme aimed at bringing back this unique reptile species.

Read more on this story at BBC News – ‘Extinct’ Galapagos tortoise may still exist.

Read the original article at Current Biology – Genetic rediscovery of an ‘extinct’ Galápagos giant tortoise species.

View photos and videos of Galapagos giant tortoise species on ARKive.

Liz Shaw, ARKive Species Text Author

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