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Oxygen boost helps dragonflies go large

Posted on behalf of Amanda Mascarelli

Back in the Permo-Carboniferous era, some 250-300 million years ago, our atmosphere was much richer in oxygen. There were also some monster insects on the prowl, and it’s long been hypothesised that the enriched air was a vital prerequisite for their survival.

Hyperoxic Dragonfly.jpgToday, the air we breathe is around 21% oxygen; back then, it was as high as 35%, according to some estimates. Could this be the factor that created dragonflies with wingspans upwards of 70 centimetres, and relatives of today’s millipedes that were up to two metres long?

At the annual meeting of the Geological Society of America here in Denver, Colorado, John VandenBrooks, a paleontologist from Arizona State University in Tempe, presented experimental evidence which supports that link between oxygen and insect gigantism. (for more, see this press release)

VandenBrook’s group believe that insects may be particularly sensitive to atmospheric changes in oxygen because insects take in oxygen through their trachea (hollow tubes that transport air into their bodies) rather than receiving oxygen through blood, as many animals do.

To test the idea, VandenBrook and his colleagues reared insects in the lab under varying oxygen concentrations and studied the changes in body growth and trachea size. Cockroaches did not grow any bigger than normal under different oxygen conditions, but dragonflies grew 20 percent larger when reared with a 10 percent increase in oxygen.

They also compared the sizes of fossilized insects, and are now imaging insects trapped in amber to look closely at the sizes of insect trachea tubes, with hopes that this might provide a suitable proxy that will allow them to estimate oxygen levels on ancient Earth.

Some of these results were published earlier this year in Proceedings of The Royal Society B and the team promises that it has additional publications on the way.

(You can also read more about oxygen and insect gigantism in Nick Lane’s excellent book Oxygen).

Image: Elyse Munoz 2010

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