The adventurousness of Tortoises

Gallery

Do you know about the rafting dispersal theory?

It’s all about animals and islands and new continents, and how the former manage to get on the latter. How were islands such as the galapagos colonised? And how did giant tortoises come to live on all (or nearly) islands of the Seychelle archipelago, with Madagascar, the Mauritius and Reunion included? Check these out on a map – they’re pretty far. And, come to think of it, what about lemurs on Madagascar? Impossible to think that the same species (that then branched into subspecies) evolved on different islands from different ancestors – a genetic impossibility!

The Joy of Knowledge published by Mitchell Beazley in 1987

An image of the rafting dispersal theory, from “The Joy of Knowledge”, published by Mitchell Beazley in 1987

So scientists thought – aha! Some animals must have floated out towards these islands, maybe during storms, by pure chance, while they were grazing on a bunch of leaves for example, or on logs, or clumps of land that accidentally got disconnected from their original continent/island. They’d be sitting on a particularly comfortable raft, with food, and if not seabird, mammal or fish snacked on them on the way, the whole event could have led to a happy ending and successful colonisation of a new territory, right?

(in the image below, taken from this interesting article, some animals that we’re practically sure rafted along from one continent to an other)

Cantner_RaftingMap

In 2004, a brave little tortoise (ok, I’m using a cute name to appeal to the less scientific crowd, I admit it) was found floating in the sea, nearly on land, close to Kimbiji, Tanzania.

Aldabra giant tortoise, floating, sea, dispersal, raft

Photo by Adam White, not of the tortoise in question

No raft, no nothing. It landed safely thanks to survival skills that would make Bear Grylls blush with embarrassment:  a natural buoyancy (head up!), a tendency to live up to six months without food or fresh water and a tough, tough skin. No one was quite sure where it had come from…

kimbiji-tortoise-map

the hypothesised 740km journey the tortoise probably made

…but one thing was clear: it had been in the sea a long, long time. Based on the barnacles on the extraordinary female tortoise, she had been floating around for at least 7 weeks.

kimbiji-tortoise

Check out her barnacles!

Hungry, thirsty and exhausted, she was taken to a breeding center in Dar Es Salaam and, as far as the internet knows, is still alive and well. Here you can read the article about her journey, and here you can read some informal stuff on oceanic dispersal.

Incredible, huh?

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