student activity
8.2 Case study 1: study of respiration and tracheal function in
insects
Articles can be found at:
•
http://chronicle.uchicago.edu/030206/insects.shtml
•
http://www.synchrotron.vic.gov.au/files/documents/beetles_final_18July.pdf
Section 8.2
Page 153
BIOLOGY
Breathtaking beetles discovery
➔
A team of American researchers has used the high intensity x-rays
generated by a synchrotron to observe for the first time how insects
breathe.
The researchers — from the Field Museum of Natural History in Chicago and the
nearby Argonne National Laboratory — were able to take x-ray videos using a
synchrotron, which showed that insects can breathe actively, in a manner similar to
mammals. Not only does this finding contradict what was previously thought, it also
explains how an insect can pump enough oxygen to its head and extremities to
support complex nerve, sensory and muscular systems.
High intensity x-rays of the ground
beetle, Platynus decentis (top),
show the expanded and
compressed tracheal tubes, half a
second apart
“This research used a new technique for obtaining x-ray videos of living small
animals at micron (one thousandth of a centimetre) resolution,” says Mark Westneat,
associate curator of zoology at the Field Museum. “[It used] the synchrotron x-ray
beam at Argonne National Laboratory to generate real-time phase-enhanced x-ray
images that may revolutionise the study of biomechanics in small animals.”
Insects distribute air throughout their bodies via a network of tubes called tracheae,
which range from bulk trunk pipelines to tiny tubules that service individual cells. The
network connects to the air outside by means of vents known as spiracles along the
side of the body. These can be opened and closed.
It had been assumed the tracheae remained relatively rigid, and that air diffused in,
out and around the system passively, in some cases assisted by the muscular
buffeting of movement, particularly flight. No one had actually seen inside an insect
to verify this, because insects are covered by an opaque cuticle or exoskeleton.
PICTURES: MARK WESTNEAT, THE FIELD MUSEUM, CHICAGO
The approach used by the group can now be applied to unravelling the internal
secrets of many other small organisms, providing information that may be important
to human health.
All that changed the day physicist Wah-Keat Lee scrutinised a dead ant under the powerful x-ray beam of
the Advanced Photon Source at Argonne. He found he was able to look right through the cuticle. Edge
enhancement techniques revealed, for the first time, the ant’s complex internal structure. Lee became so
enthralled, he went looking for entomologists to help him further explore the inner world of insects.
The Field Museum/Argonne team have now used the synchrotron to look at a wide range of live insects
including beetles, crickets, ants, butterflies, cockroaches, earwigs and dragonflies. Three species — wood
beetles, carpenter ants, and house crickets — were studied in detail.
The researchers found that far from being rigid, the tracheae can be compressed and relaxed laterally so
that the tube cross-section can go from being circular to elliptical and back again. This can be done locally
or across whole segments, and pushes air around the system. It can also occur with the spiracles open —
sucking air in or expelling it — or closed.
Not all insects breathe actively, but those that do, respire rapidly, exchanging up to half the air in their
main tracheal tubes every second, similar to a person
Participants
involved in mild exercise.
The mechanism for powering the tracheal compression has
yet to be determined, but researchers suspect the system is
driven by the contraction of muscles in the jaw and the
limbs. Once these muscles relax, the tracheae move back
to their circular cross-section, driven by rings of horny,
elastic material in their walls.
Other projects could have spin-offs for human health.
Understanding how larval fish move their backbones, for
instance, may help in the treatment of spinal cord injuries,
and studying the workings of beetle hearts may provide
information on high blood pressure.
The Field Museum of Natural History, Chicago, Illinois;
Advanced Photon Source, Argonne National Laboratory,
Argonne, Illinois.
Project
Study of respiration and tracheal function in insects.
Technique/Application
X-ray videos of living insects incorporating edge
enhancement techniques at the Advanced Photon
Source, Argonne National Laboratory, Argonne, Illinois.
More information
Westneat et al (2003) Tracheal respiration in insects
visualized with synchrotron x-ray imaging, Science 299:
558-560; www.anl.gov/OPA/news03/news030124.htm.
Australian Synchrotron
For more information contact: Australian Synchrotron Project, Department of Innovation, Industry & Regional Development
GPO Box 4509RR Melbourne Victoria 3000 E-mail: contact.us@synchrotron.vic.gov.au Website: www.synchrotron.vic.gov.au