CHICAGO--Scientists have discovered a surprising new insect breathing mechanism that is analogous to lung ventilation in humans. "The discovery of this fundamental aspect of respiratory biology for insects could revolutionize the field of insect physiology," says Mark Westneat, associate curator of zoology at The Field Museum and lead author of a study to be published as the cover story of Science Jan. 24, 2003.
Insects - the most numerous and diverse group of animals - don't have lungs. Instead, they have a system of internal tubes called tracheae that are known to exchange oxygen through slow, passive mechanisms, including diffusion. But this study demonstrates that beetles, crickets, ants, butterflies, cockroaches, dragonflies and other insects also use rapid cycles of tracheal compression and expansion in their head and thorax to breath.
Tracheal compression was not found for all types of insects studied, but for those where it was found compression patterns varied within individuals and between species. The three species most closely studied (the wood beetle, house cricket and carpenter ant) exchange up to 50% of the air in their main tracheal tubes approximately every second. This is similar to the air exchange of a person doing moderate exercise.
Promising new technique
Up until now, it has not been possible to see movement inside living insects. This problem has been solved by using a synchrotron, which generates one of the strongest x-ray beams in the world, to obtain x-ray videos of living, breathing insects. "This is the first time anyone has applied this technology to study living insects," says co-author Wah-Keat Lee, a physicist at the Argonne National Laboratory.
A synchrotron is a large, circular, particle accelerator. The one at Argonne, called the Advanced Photon Source, has a circumference of about one kilometer and accelerates electrons almost to the speed of light. Doing this generates radiation, including x-rays that are more than one billion times as intense as conventional x-ray source. With synchrotron radiation, structures that once baffled researchers can now be analyzed precisely.
About two years ago, using a phase-enhanced imaging technique, Lee placed a dead ant in the path of the x-ray beam and was amazed to see incredibly detailed images of the ant's internal organs. He searched the Internet for a biologist who might be interested, and he and Field Museum scientists have been working together ever since.
One aspect of the technique that makes the videos so revealing is edge enhancement, which highlights the edges of some internal organs. This effect is due to the special properties of the x-ray beams at synchrotron facilities, such as the Advanced Photon Source. "It's almost as if parts of the anatomy have been outlined in pencil, like a drawing in a coloring book," Lee explains.
This work opens up the possibility of developing a powerful new technique for studying how living animals function, he adds.
Indeed, Westneat, Lee and their coauthors are already aiming the synchrotron at the jaws of insects to see how they chew. "Most of the twelve moving parts in an insect's jaw mechanism are internal, so our inability to see inside living, moving insects has prevented us from understanding how these parts work together," Westneat says.
Down the road, Westneat envisions using synchrotron x-ray videos to study a wide variety of animal functions, biomechanics and movements. New discoveries about animal function can have broad implications. For example, active tracheal breathing in the head and thorax among insects may have played an important role in the evolution of terrestrial locomotion and flight in insects, and be a prerequisite for oxygen delivery to complex sensory systems and the brain, the authors say.
This would not only help scientists learn more about the animals studied but also provide insights on human health. For example, studying how larval fish move their backbones could shed light on how to treat spinal chord injuries in humans. Likewise, studying the walls of blood vessels in mice and the tiny hearts in beetles (each beetle has eight to ten hearts) could shed light on how to treat high blood pressure.
"Basic principles of mammal, fish or insect physiology and function could have important implications for health care," Westneat says. "We intend to develop this novel technique for a range of applications that will greatly improve our knowledge of how tiny animals live and function."
NOTE JPG images available via email:
Researchers shined an Advanced Photon Source synchrotron x-ray beam through the head and thorax of this wood beetle, Platynus decentis, to view the compression and expansion of tracheal tubes. They discovered that insects breathe rapidly in a manner similar to lungs. Tracheal tubes are visible at the junction between the head and thorax. Photograph: Mark Westneat, Courtesy of The Field Museum
X-ray images of the wood beetle, Platynus decentis, taken at the Advanced Photon Source, Argonne National Laboratory. Upper: beetle tracheal tubes fully expanded. Lower: beetle tracheal tubes fully compressed. Images are about 0.5 seconds apart. Beetles and other insects can inhale and exhale one-half the volume of their large trachea, similar to the volume of human lungs during mild exercise. Photograph: Mark Westneat, Courtesy of The Field Museum