High oxygen super-sizes dragonflies, ASU study reports


Margaret Coulombe

"High oxygen levels spawn monster dragonflies," Wired reporter Dave Mosher's headline stated. Mosher was one of many inspired to write about the intriguing research that John VandenBrooks undertakes to understand how gigantism of some insects may have emerged in the Paleozoic era, roughly 300 million years ago.

While one can't go back literally in time to study those insects of the ancient past, VandenBrooks' studies, presented at the Geological Society of America's annual meeting in Denver, Colorado on Nov. 1, examined 11 "living fossils," modern day relatives of giant ancients. VandenBrooks, a postdoctoral fellow in the laboratory of School of Life Sciences' Professor Jon Harrison, manipulated the oxygen levels that these 11 insects experienced as they maturated.

His findings showed that dragonflies and beetles grown in 31 percent oxygen, the level found during the Paleozoic, were up to 15 percent larger than those grown at the 21 percent oxygen level that's found today. A third test looked at insects' growth in 12 percent oxygen, believed to be the lowest level of oxygen experienced on Earth, roughly 240 million years ago. All, but two species' growth, were stunted by the lowest oxygen levels in the test.

The article goes on to report that measurements of insect breathing-tube volume by VandenBrooks could then be correlated with those of insects trapped in amber, "offering a solid tool to determine oxygen levels in poorly understood eras."

VandenBrooks is quoted as saying that tracheal volume may be tied to prehistoric dragonfly body size: "As you become a larger insect more of your body is taken up by tracheal tubes. Eventually you reach a limit to how big you can be. The more oxygen that is available, the smaller that system needs to be and the bigger that you can grow." 

VandenBrooks studies with cockroaches revealed another outcome, slower growth, smaller tracheae, and no change in size. The report says that more studies into the fossil record, amber, oxygen and dragonflies will allow VandenBrooks to ask more questions about Earth's past inhabitants. "We want to know how it affects their metabolism," VandenBrooks said. "How does it affect their ability to perform? Their speed? Their efficiency? I'd love to know these things."

Listen to the BBC interview with VandenBrooks at: