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First published online December 22, 2003
Journal of Experimental Biology 207, 497-508 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.00767

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Development of respiratory function in the American locust Schistocerca americana I. Across-instar effects

Kendra J. Greenlee^* and Jon F. Harrison

Section of Organismal, Integrative, and Systems Biology, School of Life Sciences, Arizona State University, PO Box 874601, Tempe, AZ 85287-4601, USA

View larger version (23K): [in a new window]   Fig. 1. Determination of critical oxygen partial pressure (Pc). This is the raw data file from an individual grasshopper, showing CO2 emission (solid line) and atmospheric O2 (broken line). As oxygen partial pressure (PO2) drops incrementally, CO2 transiently increases. Briefly, we compared 95% confidence intervals constructed around the mean CO2 p.p.m. in each box. Box A is the PO2 where CO2 was significantly less than at the next higher PO2 (box B) and less than the average CO2 at all higher PO2s (box C).

View larger version (10K): [in a new window]   Fig. 2. Wet body mass increased with instar for Schistocerca americana.

View larger version (13K): [in a new window]   Fig. 3. Absolute CO2 emission (CO2) in normoxia as a function of wet body mass. CO2 scaled with body mass to the 0.73 power; r2=0.77, P<0.001.

View larger version (16K): [in a new window]   Fig. 4. Effect of decreasing atmospheric oxygen partial pressure (PO2) on mass-specific CO2 emission (CO2) and mass-specific O2 consumption (O2) for adult grasshoppers. Critical oxygen pressures (Pc) were similar for both indices of metabolic rate. The inset depicts the respiratory exchange ratio (RER) for these animals as atmospheric PO2 decreases to the Pc. RERs at 0 and 0.6 kPa O2 are off scale and are not shown; N=8 for each treatment group.

View larger version (21K): [in a new window]   Fig. 5. Effect of exposure time on mass-specific CO2 emission (CO2) responses to decreasing levels of atmospheric PO2 in adult (diamonds) and first-instar (circles) grasshoppers. One hour exposures (open symbols) are compared with 3 min exposures (solid symbols). Values are means ± S.E.M.; N=8 for each treatment group.

View larger version (20K): [in a new window]   Fig. 6. Effect of decreasing atmospheric oxygen partial pressure (PO2) on mass-specific CO2 emission (CO2) for first-instar (circle), third-instar (square), fifth-instar (triangle) and adult animals (diamond). Values are means ± S.E.M.; N=8 for each treatment group.

View larger version (12K): [in a new window]   Fig. 7. Critical oxygen partial pressure (Pc) values for mass-specific CO2 emission (CO2) determined in multiple ways and for abdominal pumping versus instar. Each symbol indicates the median; error bars mark the 25th and 75th percentiles. (A) Pc for CO2 determined using 95% confidence intervals (N=8 for each treatment group), (B) Pc for abdominal pumping (N=8 for each group), (C–E) Pc determined as the oxygen partial pressure (PO2) when CO2 decreases below 75%, 50% or 25% of normoxic CO2 (N=8 for each group) and (F) Pc determined using paired t-tests to identify the first PO2 at which mean CO2 from Fig. 6 was significantly lower than normoxic CO2.

View larger version (24K): [in a new window]   Fig. 8. Effect of decreasing atmospheric oxygen partial pressure (PO2) on abdominal pumping frequency for first-instar (circles), third-instar (squares), fifth-instar (triangles) and adult animals (diamonds). Values are means ± S.E.M.; N=8 for each treatment group.

View larger version (13K): [in a new window]   Fig. 9. Percent change in abdominal height during abdominal pumping at various oxygen partial pressures (PO2s) for adults (diamonds) and first instars (circles). Values are means ± S.E.M.; N=8 for each treatment group.

View larger version (9K): [in a new window]   Fig. 10. Maximal tracheal system conductance (Gmax) versus instar. Circles are from short-term exposures; diamonds represent long-term exposures. Values are means ± S.E.M.; N=8 for each treatment group.

View larger version (8K): [in a new window]   Fig. 11. Mass-specific CO2 emission (CO2) in anoxia divided by CO2 in normoxia as a function of instar. CO2 in anoxia was measured over 3 min after exposure to progressively more hypoxic gases (Fig. 6). Values are means ± S.E.M.; N=8 for each treatment group.

View larger version (18K): [in a new window]   Fig. 12. Index of gas exchange per breath (CO2 in µmol g–1 min–1 divided by abdominal pumps min–1) as a function of oxygen partial pressure (PO2) for first-instar (circle), third-instar (square), fifth-instar (triangle) and adult animals (diamond). Values are means ± S.E.M.; N=8 for each treatment group.

View larger version (17K): [in a new window]   Fig. 13. Critical pressure (Pc) versus normoxic mass-specific CO2 emission (CO2). The broken line shows the relationship when third instars are not included in the regression. The solid line occurs when third instars are included in the regression; N=8 for each treatment group.