Researchers at the U.S. Department of Energy's Argonne National Laboratory have cast new light on why the giant insects that lived millions of years ago disappeared.
In the late Paleozoic Era, with atmospheric oxygen levels reaching record highs, some insects evolved into giants. When oxygen levels returned to lower levels, the insect giants went extinct.
The basis of this gigantism is thought to lie in the insect respiratory system. In contrast to vertebrates, where blood transports oxygen from the lung to the cell, insects deliver oxygen directly through a network of blind-ending tracheal tubes. As insects get bigger, this type of oxygen transport becomes far less effective. But if the atmospheric oxygen levels increase, as they did in the late Paleozoic, then longer tracheal tubes can work. This would allow larger-sized insectseven giantsto evolve.
Recent research published in the journal Proceedings of the National Academy of Science helps confirm the hypothesis that the tracheal system actually limits how big insects can be. The research provides a specific explanation for what limits size in beetles: the constriction leading to the legs.
A collaborative team of researchers from Argonne's Advanced Photon Source (APS), Midwestern University and Arizona State University wanted to study how beetles' tracheal systems change as their body sizes increase. The team took advantage of richly detailed X-ray images they produced at the APS to examine the dimensions of tracheal tubes in four beetle species, ranging in body mass by a factor of 1,000.
Overall, they found that larger beetle species devote a disproportionately greater fraction of their body to tracheal tubes than do smaller species.
The team focused in particular on the passageways that lead from the body core to the head and to the legs. They reasoned that these orifices may be bottlenecks for tracheal tubes, limiting how much oxygen can be delive
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Contact: Sylvia Carson
scarson@anl.gov
630-252-5510
DOE/Argonne National Laboratory
10-Aug-2007