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First published online August 17, 2006
Journal of Experimental Biology 209, 3476-3483 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02343
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Intraspecific variation in tracheal volume in the American locust, Schistocerca americana, measured by a new inert gas method

Hilary M. Lease1,*, Blair O. Wolf1 and Jon F. Harrison2

1 Department of Biology, University of New Mexico, Albuquerque, NM 87131, USA
2 School of Life Sciences, Arizona State University, Tempe, AZ 85287-4501, USA


Figure 1
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  		Fig. 1. Experimental set-up. MFC, mass flow controllers; computer-controlled solenoid valves.

 

Figure 2
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  		Fig. 2. Data showing validation of method parameters. Each data point represents measurement of helium emitted from a single animal in one trial after completing the experimental protocol (i.e. an entire sequence of heliox exposure, nitrox flushing of chamber, and sealed chamber equilibration; helium assessed by gas chromatography of an air sample from the chamber). Different symbols indicate different animals. (A) Helium yield from animals varied with the duration of pre-exposure to heliox if exposure durations were less than 1 min, but were relatively constant with exposures greater than 1 min. (B) Residual helium in empty chamber fell with flush time duration. (C) Helium yield from the animal increased until wash-out times exceed 2 min.

 

Figure 3
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  		Fig. 3. Magnitude of estimated tracheal volume, using the water displacement method, increases with number of pumps of the syringe plunger.

 

Figure 4
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  		Fig. 4. Water displacement (WD) method and inert gas volumetric (IGV) method comparisons. (A) Both methods predict a similar increase in tracheal volume with mass. (B) Estimate of tracheal volume using the WD method versus IGV method for the same individuals. (C) The difference between the tracheal volume estimates using the WD method versus the IGV method as a function of body size. The WD method predicted larger tracheal volumes than the IGV method, with absolute difference increasing with animal size.

 

Figure 5
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  		Fig. 5. Relationship between tracheal volume and mass within fifth instar stage (filled circles) for S. americana, overlaid on between-instar data (open circles). Between-instar data includes only early-instar sub-adults and male adults. Tracheal volume increases between instars (slope=1.30) and decreases within an instar (slope=-2.37).

 

Figure 6
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  		Fig. 6. Body size (A) and tracheal volume (B) vary with gender in adult S. americana (P<0.05). The boundaries of the boxes indicate the 25th and 75th percentiles, and the whiskers above and below the box indicate the 90th and 10th percentiles.

 

Figure 7
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  		Fig. 7. Relationship between tracheal volume and mass for adult S. americana. Tracheal volume decreases with body size in adults (slope=-1.34).

 

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© The Company of Biologists Ltd 2006