Why Evolution is True is a blog written by Jerry Coyne, centered on evolution and biology but also dealing with diverse topics like politics, culture, and cats.
I’ve only just learned that today, Monday, May 23, is World Turtle Day. Jerry noted the holiday in today’s Hili Dialogue, but I missed it, so my apologies for posting so late in the day.
The day is sponsored by American Tortoise Rescue, so I thought it appropriate to share a video of Zelby, a tortoise who is an acquaintance of mine.
Zelby is a member of the genus Testudo, and is one of the species from the Mediterranean area which also extend eastward into Asia. The species might be T. horsfieldi, the Russian Tortoise. There are several forms of this group popular in the pet trade; the alpha systematics is still in flux, and I don’t know the group well.
Zelby is dining on mixed greens and cucumber slices.
Last month Matthew asked me about herbivory in reptiles, and part of my reply was that there are few or no reptiles that are exclusively herbivorous. The ones that came closest that I could think of were the true land tortoises (family Testudinidae, sensu stricto). I wrote, “some true tortoises are pretty close to vegetarian, but I’d still say they are at least facultatively omnivorous.” And sure enough, shortly after I ran into the following:
The video, of a giant tortoise (Aldabrachelys giganteus) on the island of Fregate in the Seychelles eating a noddy (Anous tenuirostris, a member of a genus of common tropical terns), accompanied a paper on the incident published last August by Anna Zora and Justin Gerlach in Current Biology. Wikipedia makes an amusing observation about noddies:
Anous is Ancient Greek for “stupid” or “foolish”. Noddies are often unwary and were well known to sailors for their apparent indifference to hunters or predators.
The sailors were right– the noddy, it seemed to me, though not fledged, could have gotten away. Perhaps it had a strong aversion to moving away from the immediate vicinity of its nest.
We’ve encountered island biologist Justin Gerlach before here at WEIT, where I noted his paper on an Aldabran tortoise’s ocean journey.
An Aldabra tortoise that came ashore at Kimbiji, Tanzania, in December 2004. Note the barnacles acquired during its adventure at sea. Photograph: C. Muir. Figure 1 of Gerlach et al. (2006)
We’ve encountered Justin Gerlach before here at WEIT, where I noted his paper on an Aldabran tortoise’s ocean journey (picture just above). The Fregate tortoises are probably introduced from Aldabra, but the systematics of Indian Ocean tortoises is not entirely settled, and there have been a number of claims of tortoises surviving from the Seychelles populations that are usually thought extinct.
As far as reptile feeding in general goes, snakes, crocodilians, and the tuatara are exclusively carnivorous (in the broad sense of feeding on any kind of animals, including carrion), lizards range from carnivorous to omnivorous with a large herbivorous component (e.g. iguanas), and turtles are omnivorous, ranging from mostly carnivorous (e.g. snapping turtles) to mostly herbivorous (e.g. true tortoises).
Gerlach, J., C. Muir and M.D. Richmond. 2006. The first substantiated case of trans-oceanic tortoise dispersal. Journal of Natural History 40(41–43): 2403–2408.
Zora, A. and J. Gerlach. 2021. Giant tortoises hunt and consume birds. Current Biology 31: R989-R990.
In the paper, they report an Aldabra tortoise that came ashore on a beach in Kimbiji, Tanzania in 2004. After considering several possibilities, they conclude that the tortoise had floated in from Aldabra, over 700 km away across the Indian Ocean. The copious growth of large barnacles on the limbs and lower parts of the carapace certainly suggested that the tortoise had spent a considerable amount of time in the sea.
The Aldabra tortoise at Kimbiji, shortly after its discovery in December 2004. Photograph: C. Muir. Figure 1 of Gerlach et al. (2006).
Dennis’s video shows that the tortoises enter water, and how they move about in the shallows. The Kimbiji tortoise, despite the ability to swim, could not have swum to the main, but was rather mostly carried by the currents, and presumably spent its time at sea keeping its head, and most of the dome of its carapace, above water. It was, however, walking ashore, apparently intentionally, when found.
So why is this important? It has long been supposed that animals and plants get to oceanic islands by what Darwin called “occasional means of transport“: carried along on logs, masses of vegetation, ice floes, attached to birds, or floating by themselves in the water. (Darwin carried out a series of experiments on the ability of various plant seeds to float in sea water, and their ability to germinate after varying periods of immersion.) Tortoises have usually been thought to float by themselves because of the difficulty they would have in clinging to vegetation, and also because the practice of mariners of earlier centuries of putting giant tortoises in the holds of their ships as a living food supply had shown that tortoises could live for many months without food or water.
Although Darwin and many subsequent zoogeographers (e.g., P.J. Darlington) invoked such occasional means of transport, there has always been a school of thought arguing that such crossings of the ocean by land animals were nigh impossible, and that the presence of non-flying land animals on an island implied a past land connection. In the first half of the 20th century, this school constructed speculative land bridges crisscrossing the oceans, in order for every island animal to have had a dry-shod passage to the island from its home of origin. In the later 20th century, with the development of plate tectonics, the land bridge builders were succeeded by drift enthusiasts, who thought drifting crustal plates could serve to bring oceanic islands into juxtaposition with continents, so that, again, animals might get to islands without having to cross water (or at least not much). (The drift enthusiasts had the advantage that continental drift actually does occur, even if not in the exact plate configurations they hoped for, whereas the land bridge builders’ long, thin isthmuses crossing abyssal oceans have not been borne out by geology.) So, the more or less direct observation of transoceanic crossing by an occasional means of transport provides a crucial link—a vera causa—in the argument for the occurrence and importance of such means in the colonization of islands.
Some younger biologists, raised (and properly so!) on plate tectonics, and perhaps lacking acquaintance with older literature and island organisms in the field, had taken the drift enthusiasts’ claims too much to heart, and seemed to be unaware of the importance of transoceanic dispersal. Now that molecular phylogenies often bolster the argument for the importance of occasional means of transport, they seem a bit surprised to find out that there indeed has been a lot of ocean crossing, not just to oceanic islands, but between continents and continental islands as well. We discussed one such case here on WEIT, the ratite birds, where what had seemed to actually be a good case for continental drift seems to actually involve a fair amount of oceanic crossing. The zoologist Alan de Queiroz has written a popular book on the biology of oceanic dispersal, and the sociology of its rediscovery by some biologists.
de Queiroz, A. 2014. The Monkey’s Voyage: How Improbable Journeys Shaped the History of Life. Basic Books, New York.
Gerlach, J, C. Muir and M.D. Richmond. 2006 The first substantiated case of trans-oceanic tortoise dispersal. Journal of Natural History 40(41–43): 2403–2408. pdf
Darwin lived in the country, and had many animals– for companionship, work, and research. For companions, his chief pets were d*gs (my favorite of Darwin’s d*gs was Bob), but he also had a tortoise that he brought home from James (Santiago) Island in the Galapagos. It has been claimed (most notably by the late Steve Irwin of Crocodile Hunter fame) that this tortoise later made its way to Australia, where it was named Harriet and lived to be about 175 years old. I always thought this story had dubious links in its chain of evidence, and Paul Chambers, in A Sheltered Life: The Unexpected History of the Giant Tortoise, after an exhausting examination, considered the story untrue.
A Galapagos tortoise from James (Santiago) Island, once owned by Charles Darwin. BM(NH) 1874.6.1.6, formerly 37.8.13.1.
Unbeknownst to me, four years ago Aaron Bauer and Colin McCarthy revealed the true fate of Darwin’s tortoise: it’s in the Natural History Museum in London, which is pretty much where you would have expected it to wind up. Henry Nicholls in the Guardian, in a Darwin Day tortoise piece, reminds us all of this fact, telling some of the details of the specimen’s history and rediscovery.
McCarthy, at the time the herpetology collection manager, found it in a store room in March of 2009, while preparing a list of Darwin specimens in the collection. Its original registration number shows it was catalogued on August 13, 1837, so it lived only a relatively short while after getting to England.
I am not at all surprised that it turned up at the Natural History Museum, nor that it was lost track of. The big, older, museums have large collections, and earlier curation policies were not up to today’s standards. There’s an old story, perhaps apocryphal, that a British paleontologist once submitted a grant application to fund an expedition to the basement of the museum!
According to Nicholls, you get to see the tortoise as part of the “Spirit Collection Tour” at the museum. “Spirit” refers not to the departed specimens’ souls, but to their method of preservation: in spirits. (Such specimens are called “alcoholics”, which causes some initial confusion when referring to them in front of a non-museum audience).
Bauer, A.M. and C.J. McCarthy. 2010. Darwin’s pet Galápagos tortoise, Chelonoidis darwini, rediscovered. Chelonian Conservation and Biology 9:270-276. abstract
Chambers, P. 2004. A Sheltered Life: The Unexpected History of the Giant Tortoise. John Murray, London (American edition, 2006, by Oxford University Press, New York). OUP
Addendum: In response to a reader’s request, I append a photo of Bob (as well as much of the rest of the Darwin family) at Down House ca. early 1860s.
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 (Charles, Santa Maria) Island tortoise. Gunther 1902, plate XVI
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.
Floreana (Charles, Santa Maria) Island tortoise. Gunther 1902, plate XVII
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.
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
This young tortoise is having a hard time getting a bite of this piece of tomato.
I’m not sure what kind of tortoise it is– it looks like a member of the genus Testudo, which consists of about four species with a bunch of subspecies from southern Europe, northern Africa, and western Asia (see tortoise references below). [UPDATE: Testudo are fairly common in the pet trade– can anyone identify the little feller? UPDATE II: Readers Christopher McLaughlin and Derek have identified it as Geochelone sulcata, a species from the Sahel-Sudan region just south of the Sahara. ]
The tortoise’s seeming inability to adjust its angle of attack reminds me of the behavior of lizards I have fed by putting food in a clear glass dish. They see the food, and keep butting their head into the side of the dish, not realizing that if they lifted their head up, and then bit down over the side of the bowl, they’d get it.
Cats are familiar with the concept of glass, and know, for example, how to enter a room via the open part of a sliding glass door, and don’t keep walking into the glass.
M. Le, C.J. Raxworthy, and W.P. McCord. 2006. A molecular phylogeny of tortoises (Testudines: Testudinidae) based on mitochondrial and nuclear genes. Molecular Phylogenetics and Evolution 40:517-531. pdf
Rhodin, A.G.J., J.B. Iverson, and H.B. Shaffer. 2010 Turtles of the world, 2010 update. Chelonian Research Monographs 5:85-164. pdf
As a herpetologist with a cat, I’m always interested in feline-reptilian interactions, and here’s a South African tortoise that either doesn’t like cats, or likes them so much that it gets close enough to annoy them and drive them away. Note that the orange tabby, at least, appears to regard its interactions with the tortoise as playful, much as Peyton regards her interactions with me (in the second video), thus demonstrating, once again, the rudimentary moral sentiments of cats. (Try to ignore the dreadful soundtrack.)
This clip from South African TV provides the context of the clip.
The original video by Salvelio Meyer, sans soundtrack, has had embedding disabled, but you can see it at Youtube, by clicking through the image below.
