by Greg Mayer
The recent untimely passing of Lonesome George, the last living individual of the Galapagos tortoise subspecies from Pinta (Abingdon) Island, reminds me of a paper from earlier this year, which holds out some hope for the Pinta tortoises. In that paper, in Current Biology, Ryan Garrick and colleagues presented evidence for the continued existence of the Floreana (Charles, Santa Maria) Island tortoise. The evidence is indirect, but very interesting.
Floreana was much visited by buccaneers and whalers, and was the first of the Galapagos islands to be colonized (in 1832). Consequently, its tortoises took it on the chin earlier than most. The last tortoises known to have been collected on the island were taken in the 1830s, and the race is supposed to have been extinct by about 1840. One of the things that made tortoises attractive to mariners was that they could survive long periods of time in the holds of ships, which sometimes led to live tortoises being brought to other islands, and, at least occasionally, their release back into the wild.
Genetic evidence of this mixing of island tortoise populations was found by Nikos Poulalakis and colleagues. Using DNA recovered from museum specimens collected in the 19th century, Poulalakis et al. found the Floreana tortoises genetically distinctive, and that some of the Floreana genetic material was present in tortoises from the island of Isabela (Albemarle). (Michael Russello and colleagues have also found evidence of Floreana ancestry in captive tortoises.) Building on this, Garrick et al. have now shown that some of the genetically mixed tortoises on Isabela are F1 hybrids– i.e., one of their parents was a Floreana tortoise! The F1’s were also not very rare– 84 were identified– and some quite young (< 15 years), so the parents should still be around. So, a Floreana tortoise has not been found (hence the “sort of” in the title), but there’s a really good chance that they’re still out there, somewhere on Isabela. If found, they could then be bred together, and perhaps reintroduced to Floreana.
What does this mean for Lonesome George’s subspecies? Well, Michael Russello and colleagues found evidence of Pinta tortoise (that’s George’s subspecies) genetic material in Isabela tortoises, too. So, there might be a Pinta tortoise or two on Isabela as well. None of the genetically mixed tortoises have been identified as F1, though, so discovery of a living Pinta tortoise is a longer shot than finding a Floreana tortoise. But it will be very interesting to watch for the results of continued genetic surveys of Galapagos tortoises (most of the work is being carried out in the laboratory of Adalgisa Caccone at Yale), and keep our fingers crossed that Floreana and Pinta tortoises might turn up.
h/t: daveau, Dominic
Chambers, P. 2006. A Sheltered Life: The Unexpected History of the Giant Tortoise. Oxford University Press, Oxford.
Garrick, R.C., E. Benavides, M.A. Russello, J.P. Gibbs, N. Poulakakis, K.B. Dion, C. Hyseni, B. Kajdacsi, L. Marquez, S. Bahan, C. Ciofi, W. Tapia and A. Caccone. 2012. Genetic rediscovery of an ‘extinct’ Galápagos giant tortoise species. Current Biology 22: 10-11. pdf
Gunther, A. 1902. Testudo galapagoensis Novitates Zoologicae 9:184-192. BHL
Poulakakis, N., S. Glaberman, M. Russello, L.B. Beheregaray, C. Ciofi, J.R. Powell, and A. Caccone. 2008. Historical DNA analysis reveals living descendants of an extinct species of Galapagos tortoise. Proceedings of the National Academy of Sciences 105:15464-15469. pdf (not sure if it’s open access)
Russello, M.A., L.B. Beheregaray, J.P. Gibbs, T. Fritts, N. Havill, J.R. Powell and A. Caccone. 2007. Lonesome George is not alone among Galápagos tortoises. Current Biology 17: 317-318. pdf
Russello, M.A., N. Poulakakis, J.P. Gibbs, W. Tapia, E. Benavides, J.R. Powell, and A. Caccone. 2010. DNA from the past informs ex situ conservation for the future: an “extinct” species of Galápagos tortoise identified in captivity. PLoS ONE 5(1): e8683, 7 pp. pdf
Van Denburgh, J. 1914. Expedition of the California Academy of Sciences to the Galapagos Islands, 1905-1906. X. The gigantic land tortoises of the Galapagos Archipelago. Proceedings of the California Academy of Sciences (4th Ser.) 2: 203-374. pdf
10 thoughts on “Extinct tortoise rediscovered- sort of- and hope for Lonesome George’s clan”
Sort of a teenage mutant Pinta turtle, then. 🙂
(Yeah I know what I did wrong, but ‘Floreana’ doesn’t as nicely)
Oh, I hope no christians pray for them that will jinx them for sure.
Even if some of the creatures were found, it’s likely they’ll just be another Curiosity like George – at best that’s one hell of a bottleneck. One more “last of its kind” to attract tourists.
So does this mean we can save genes that are on the verge of extinction by breeding them with closely related species when there are not enough members of a particular subspecies left? But those would have many generations who would have birth defects and stuff I’m guessing.
Lonesome George was given the opportunity to mate with females of another subspecies, but no young resulted. This was also tried with the dusky seaside sparrow. By backcrossing to the purebred parent, you can get a fairly high proportion of the genome from the target subspecies. (The proportion purebred is 1-.5^t, where t is the number of generations, so that 5 generations gives you ~ 95% purebred.) This requires that the purebred parent be fairly long lived. And it can lead, as you suggest, to inbreeding depression.
I’m sure I could probably look this up, but how did these tortoises get there to begin with?
are there smaller, related species in SA?
did they raft there then get big (I can’t think of a plausible alternative)?
There are smaller relatives in South America. They rafted there (or, perhaps just as likely, floated without accompanying raft), and got bigger.
From Scientific American, Nov. 24, 2012