Once upon a time, dragonflies with 2-foot wingspans, millipede-like creatures 5 feet long, and other colossal insects inhabited the earth. While insect gigantism has long been seen in the fossil record, new research provides the best evidence yet that higher oxygen levels in the past spurred insect growth.
Like all animals, insects require oxygen to function; yet insects do not have lungs. Instead, holes in their exoskeletons allow air to enter a network of hollow tubes called tracheae, which branch throughout the body.
Alexander Kaiser, an insect physiologist at Midwestern University and lead author of the study, which appears in Proceedings of the National Academy of Sciences, explained the tracheal system to WORLD: "The oxygen in the atmosphere travels down those tubes directly to the cells to be delivered to the places where energy is produced. The amount of oxygen available determines how far oxygen can travel down the tube."
Using specialized X-ray technology, Kaiser and his colleagues investigated the tracheal systems of several darkling beetles ranging in length from 3 millimeters to over an inch. They found that the larger the beetle, the greater proportion of space the tracheae took up. Although larger tracheae provided the necessary oxygen to the beetle's cells, they also crowded other organs and tissue, presumably limiting the overall size to which the beetle could grow.
However, if the atmosphere's oxygen level was greater in the past, as scientists believe it was (31 percent to 35 percent, compared to today's 21 percent oxygen rate), the tracheal tubes may have been able to support larger bodies while remaining relatively small. "When [the] oxygen available is higher, the dimensions of those tracheal tubes can be smaller compared to insects that live under normal oxygen concentrations, so they take up less space, and this space is free for other tissues," said Kaiser.
To test their hypothesis, Kaiser's team raised fruit flies in an oxygen-enriched chamber and found that the insects indeed grew larger, without an exaggerated increase in tracheae size. Darkling beetles are now being raised under similar conditions. Kaiser, who said he was surprised by the team's findings, wants to analyze even larger insects in the future.
Brush those gums
HEALTH: Brushing damages cells but strengthens tissue
You already know brushing your gums is good for them, but the reason why may come as a surprise-even to your dentist. New findings in the Journal of Dental Research indicate even mild brushing rips open the cells lining the gums and tongue, called epithelial cells. The stress not only initiates a repair response to heal the cell damage, but triggers the growth of new cells, collagen, and blood vessels, maintaining firm and healthy tissue. The researchers think that brushing, besides removing bacteria and food, provides a rigorous workout that keeps gums in shape.
He's no Baby Einstein
PSYCHOLOGY: Baby videos may hinder development
Popular baby video products like Baby Einstein and Brainy Baby may be holding infants back instead of helping them. In a study published in the Journal of Pediatrics, researchers found that for every hour per day infants ages 8 to 16 months spent viewing baby videos, they understood 6 to 8 fewer words than infants who didn't watch the programs. Among toddlers (17 to 24 months) the videos produced no discernable positive or negative effect.
In a press release, study co-author Andrew Meltzoff suggested the infants' linguistic handicap resulted from parents using the videos as babysitters. He recommends "parentese"-talking to your babies yourself.