Tree lobsters’ convergent evolution
New Zealand scientists have uncovered remarkable information on the evolution of one of the world’s rarest insects – the Lord Howe Island tree lobster (Dryococelus australis).
The tree lobster is a large (up to 130 mm) ground-dwelling stick insect that was once common on Australia’s Lord Howe Island. The accidental introduction of rats from a shipwreck in 1918 led to the assumed extinction of the species by the 1960s.
The Lord Howe Island tree lobster
The Lord Howe Island tree lobster is one of the world’s rarest insects. The male (left) and female (right) of the Lord Howe Island tree lobster appear quite different. The female has an elongated secondary ovipositor (for egg laying), and the male has enlarged, powerfully armed hind legs.
Rediscovery of the tree lobster
In 2001, a small population was discovered on Balls Pyramid, a very small 200 m-wide rock pyramid approximately 25 km from Lord Howe Island. This population of only about 24 individuals confirmed the tree lobster as one of the world’s rarest insects. Since the discovery, a captive population was established at Melbourne Zoo and plans prepared to re-introduce the species after eradication of the rats on Lord Howe Island.
Evolution of tree lobsters
For many years, scientists have believed that the Lord Howe Island tree lobster was closely related to other tree lobsters from New Guinea and New Caledonia. They also believed that the different tree lobsters evolved from a common ancestor.
Research, including DNA analysis, by Landcare Research scientists Thomas Buckley and Dilini Attanayake along with Sven Bradler from the University of Gottingen has shown that the opposite is the case. That is, rather than divergent evolution from a common ancestor, the Lord Howe Island tree lobster is an example of convergent evolution from a different ancestor.
Dr Buckley explains that convergent evolution is where different species independently evolve to look and behave the same, usually because they evolve to occupy a very similar niche.
“We performed special analysis using DNA sequences to decipher the evolutionary affinities among tree lobsters. We discovered that they are not closely related to each other but evolved independently on separate oceanic islands. Obviously, similar selective pressure repeatedly led to the evolution of extreme convergences in form and behaviour,” he says.
“This research shows that the Lord Howe tree lobster is far more unique than previously thought and therefore its continued survival is very important.”
The research is part of Dr Buckley’s wider research on stick insects from New Zealand and the Pacific Region. It was funded by the National Geographic Society and the Foundation for Research, Science and Technology.
The scientists’ work has been published in the scientific journal Proceedings of the Royal Society B. It’s a big deal for scientists to have their research published in international journals like this, as it is recognition from their scientific peers of the value of their work.
Read the article DNA barcoding to find out more about how scientists use DNA to identify and distinguish different animal species worldwide.
