Feb. 6, 2003
Vol. 22 No. 9

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    Argonne, University scientists reveal insect respiratory function with X-rays

    X-ray images from the beamline at the Advanced Photon Source, at Argonne National Laboratory, show a ground beetle (Platynust decentis) specimen photographed twice, about 0.5 seconds apart, during the imaging study of insect respiration. Researchers found that insects breathe rapidly in a manner similar to breathing with lungs. Above, the beetle’s tracheal tubes are fully expanded, and below, they are fully compressed. Beetles and other insects can inhale and exhale one half the volume of the large trachea, similar to the volume of human lungs during mild exercise.
    Scientists at Argonne National Laboratory, the University and the Field Museum 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,” said Mark Westneat, a Lecturer in the Committee on Evolutionary Biology and Associate Curator of Zoology at the Field Museum of Natural History.

    Westneat, who is lead author of the study–published as a cover story in the Friday, Jan. 24 issue of Science magazine–teamed up with Argonne physicist Wah-Keat Lee.

    Up until now, it has not been possible to see movement inside living insects, but Lee and his collaborators found that using a synchrotron, which generates one of the strongest X-ray beams in the world, could provide X-ray videos of living, breathing insects.

    Insects–the most numerous and diverse group of animals–do not 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 breathe.

    Tracheal compression was not found for all types of insects studied, but for those in which it was found, compression patterns varied within individuals and between species. The three species most closely studied (the ground beetle, house cricket and carpenter ant) exchange up to 50 percent of the air in their main tracheal tubes approximately every second. This is similar to the air exchange of a person doing moderate exercise.

    “This is the first time anyone has applied this technology to study living insects,” said Lee, who made an initial discovery two years ago, using a phase-enhanced imaging technique. Lee had placed a dead ant in the path of the X-ray beam, which then produced incredibly detailed images of its internal organs. This finding led him to seek out a biologist interested in pursuing the investigation further. He found Westneat and began collaborating with him and other scientists at the Field Museum.

    The synchrotron at Argonne National Laboratory, called the Advanced Photon Source, is a large, circular particle accelerator that has a circumference of about one kilometer. It accelerates electrons almost to the speed of light, which generates radiation, including X-rays that are more than one billion times as intense as a conventional X-ray source. With synchrotron radiation, structures that once baffled researchers can now be analyzed precisely.

    One aspect of the technique that makes the X-ray videos so revealing is edge enhancement, where highlights appear at the edges of some insects’ internal organs. This effect is a result of 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 explained. This work opens up the possibility of developing a powerful new technique for studying how living animals function, he added.

    Indeed, Westneat, Lee and their co-authors are already aiming the synchrotron at the jaws of insects to see how they chew. “Most of the 12 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 said.

    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 may be a prerequisite for oxygen delivery to complex sensory systems and the brain, he said.

    What scientists learn about the animals they study could provide insights into human health. For example, studying how larval fish move their backbones could provide clues for treating spinal cord injuries in humans. Likewise, studying the walls of blood vessels in mice and the tiny hearts in beetles (each beetle has eight to 10 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 humans and their health care,” Westneat said. “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.”