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First published online August 31, 2004
Journal of Experimental Biology 207, 3559-3567 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.01189

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Plastic and evolved responses of larval tracheae and mass to varying atmospheric oxygen content in Drosophila melanogaster

Joanna R. Henry^* 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 (28K): [in a new window]   Fig. 1. Experimental design for the multi-generation experiments. In the oxygen selection experiment, 30 randomly chosen female flies were mated and used to found each generation. The same procedure was used to found the first generation and last two generations of the artificial selection experiment, whereas for generations two to n, only the heaviest 25% of the females were allowed to mate and found the next generation. For both experiments, flies were reared in 21% O2 in generation 0 and the final two generations. Flies were reared in 10, 21 or 40% O2 during all other generations. Two trials of both experiments were performed, each with a different relative humidity. Multiple main dorsal tracheae (DT) diameters were measured in the first trial; only posterior DT diameters were measured in the second trial. See text for details.

View larger version (40K): [in a new window]   Fig. 2. Image of a third-instar larva. Diameters of the main dorsal tracheae (DT) were measured at (a) the anterior anastomosis, (b) the second, (c) fourth, (d) sixth and (e) eighth transverse connectives and (f) the posterior anastomosis. Scale bar, 0.1 mm.

View larger version (21K): [in a new window]   Fig. 3. Larval mass vs % O2 in the plasticity trials. The asterisk denotes significant difference from 21% values (post-hoc test, P<0.05).

View larger version (20K): [in a new window]   Fig. 4. (A) Larval mass vs generation for the first multi-generation trial. Shaded regions indicate generations raised in normoxia. Asterisks indicate significant difference from the normoxic group (post-hoc test, P<0.05). (B) Larval mass vs generation of the second multi-generation trial. Shaded regions indicate normoxic conditions. Asterisks indicate significant difference from the normoxic group (post-hoc test, P<0.05).

View larger version (16K): [in a new window]   Fig. 5. Tracheal diameters vs position in the first plasticity trial (similar patterns were observed in the other trials). Alphanumerical values along the x-axis correspond to the six measurement positions described in Fig. 2, with a being the diameter at the anterior anastomosis and f being the diameter at the posterior anastomosis. Lines are defined using spline curves. Asterisks indicate a significant effect (P<0.02) of oxygen on diameter.

View larger version (17K): [in a new window]   Fig. 6. The posterior tracheal diameters of fruit fly larvae in the two plasticity trials after one generation of exposure to different oxygen levels. * shows a significant difference (P<0.05) from normoxic diameters in trial 1 and ** shows significance (P<0.05) from normoxic diameters in trial 2.

View larger version (23K): [in a new window]   Fig. 7. (A) Mean tracheal diameters over multiple generations during the first trial. Shaded areas indicate the generations during which all treatment groups were raised in normoxic conditions. (B) Tracheal diameters at the posterior anastomosis over multiple generations during the second trial. Shaded areas indicate the generations that were raised in normoxic conditions regardless of treatment line. Generations in which O2 significantly affects tracheal diameter are marked with an asterisk (P<0.05).

View larger version (23K): [in a new window]   Fig. 8. Diffusing capacities of the main dorsal tracheae (DT) in the first plasticity and multi-generation trials vs rearing oxygen partial pressure (PO2).