Hundreds of millions of years ago, dragonflies with wingspans of more than 2 feet roamed the Earth.
One ASU scientist is trying to bring them back.
John VandenBrooks, a postdoctoral research fellow at ASU, released data from his study on how oxygen levels in the atmosphere affect insect size.
VandenBrooks, who worked with several other ASU scientists on the project at the Tempe campus, presented his findings Monday at the annual meeting of the Geological Society of America in Denver, which features a series of lectures on many different subjects related to geology.
VandenBrooks and his assistants grew batches of dragonflies, cockroaches, mealworms, beetles, grasshoppers, and other insects and raised them in varying levels of oxygen, VandenBrooks said.
“Our goal with this research is to understand how varying oxygen levels in the past may have influenced insect development,” VandenBrooks said.
While the majority of Earth’s atmosphere is composed of nitrogen, oxygen levels have varied throughout history, VandenBrooks said, reaching as high as 31 percent of the atmosphere to as low as 12 percent. The current oxygen level of Earth is 21 percent.
Scientists have found that giant dragonflies existed during the Paleozoic period, around 300 million years ago, when oxygen levels were at their highest. They drew from this the hypothesis that the high levels of oxygen contributed to the massive insects’ size.
VandenBrooks, a paleontologist by trade, began his research three years ago in order to understand what factors contributed to insect growth in ancient times.
VandenBrooks and his assistants raised the insects in oxygen levels ranging from 12 to 40 percent, he said.
In 10 out of 12 cases, the insects decreased in size in low oxygen environments, but there were varying results when they were raised in high levels of oxygen.
Dragonflies, for example, increased in size by 10 to 15 percent when raised in a high oxygen environment, VandenBrooks said.
The dragonflies were difficult to raise since they’re predatory creatures and must feed on live prey, said biology senior Elyse Muñoz, one of VandenBrooks’ assistants on the project. She worked primarily with dragonfly rearing and was responsible for feeding them while in their aquatic larval stage.
“We had to hand-feed each dragonfly,” Muñoz said. She added that the research was mainly interested in the larval stage because that is where high oxygen levels have the most effect on growth.
Cockroaches did not increase in size with more oxygen, said pre-med senior and research assistant Michael Weed, although the roaches’ other physical attributes were affected.
“They’re very hardy,” Weed said. “They were easier to feed and generally maintain than the dragonflies were.”
All of the insects were sent to the Argonne National Lab’s X-ray imaging facility in Chicago to analyze their tracheal tubes, the apparatus through which they take in oxygen.
It was found that cockroaches reared in low oxygen environments developed smaller tracheal tubes, possibly allowing the insects to invest tissue in other systems, such as reproduction or digestion.
“Even though they didn’t get bigger, it still affected their physiology,” VandenBrooks said.
VandenBrooks’ research is still ongoing, he said, and he’s looking to expand his area of study to include more distant periods of Earth’s history.
Humans and insects are more similar than meets the eye, Muñoz said, as they share many of the same genes.
“Oxygen is one of the most important elements in the entire world, for humans as well as insects,” she said. “We’re really on the cutting edge at ASU.”
Reach the reporter at alex.ferri@asu.edu
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