9 January 2009

Tree lobster came from ancient sunken island

By
Cosmos Online
An ancient island utopia that sank long ago is more than a fairytale for Australia's tree lobster: it's where the strange insect may have actually evolved millions of years ago, say researchers.
Lord Howe Island tree lobster

Tree lobster: The Lord Howe Island stick insect (Dryococelus australis) is millions of years older than the island itself. Credit: Thomas Reischig

SYDNEY: An ancient island utopia that sank long ago is more than a fairytale for Australia’s tree lobster: it’s where the strange insect may have actually evolved millions of years ago, say researchers.

One species of the insect, Dryococelus australis, was previously thought to be native to Lord Howe Island, 600 km east of Australia. However, “DNA data suggests the Lord Howe tree lobster is actually older than Lord Howe Island itself,” says Thomas Buckley, a New Zealand-based zoologist studying the species.

Ball’s Pyramid

The tree lobster, a ground dwelling stick insect, previously lived in abundance on Lord Howe Island. But in 1918, a shipwreck brought rats onto the island, pushing the species to extinction – or so it was thought. In 2001, a small population of the creatures was found on a rocky outcrop just 25 km from the island known as Ball’s Pyramid.

Buckley recently led a study on the insects published in the Proceedings of the Royal Society B in December 2008.

The study looked at the DNA of stick insects or phasmids, a group that includes tree lobsters from Lord Howe, New Guinea and New Caledonia along with other stick insects. The information was then used to create a family tree of the insects, showing how closely different species were related.

The team was surprised to find that the Lord Howe tree lobster was 22 million years old, much older than Lord Howe Island itself, which has only been in existence for 7 million years.

Despite its name, the Lord Howe tree lobster is not actually native to the island (and is not a lobster): the study showed that it wasn’t even closely related to the tree lobster species in New Guinea or New Caledonia either.

Typically, stick insects live on trees and bushes, blending into their surrounding. Tree lobsters are different as they have adapted to ground dwelling life. According to the research, the three species evolved this ability separately, a process called convergent evolution. This explains why the Lord Howe, New Guinea and New Caledonian species don’t appear to be related.

Drowned island

The only remaining mystery was where the Lord Howe tree lobster originated. Buckley believes that the species must have either evolved in Australia, or on a now drowned island north of Lord Howe Island, which was once part of a larger archipelago.

The insects simply expanded across the island chain, until they reached to Lord Howe, which became the only island to survive into the present day.

Using DNA to construct a family tree “is the best we have at the moment to ‘go back in time’ and reconstruct the evolution of a given group” says Marco Passamonti, an expert on stick insects based at the University of Bolona in Italy, “This seems to me a very good study, well supported and with sound data.”

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