Abdominal pumping in caterpillars has only been documented during molting. Using synchrotron X-ray imaging in conjunction with high-speed flow-through respirometry, we show that Manduca sexta caterpillars cyclically contract their bodies in response to hypoxia, resulting in significant compressions of the tracheal system. Compression of tracheae induced by abdominal pumping drives external gas exchange, as evidenced by the high correlation between CO2 emission peaks and body movements. During abdominal pumping, both the compression frequency and fractional change in diameter of tracheae increased with body mass. However, abdominal pumping and tracheal compression were only observed in larger, older caterpillars (>0.2 g body mass), suggesting that this hypoxic response increases during ontogeny. The diameters of major tracheae in the thorax increased isometrically with body mass. However, tracheae in the head did not scale with mass, suggesting that there is a large safety margin for oxygen delivery in the head in the youngest animals. Together, these results highlight the need for more studies of tracheal system scaling and suggest that patterns of tracheal investment vary regionally in the body.
K.J.G., S.D.K. and W.-K.L. concieved this study and designed the experiments. Experiments were executed by K.J.G., S.D.K., W.-K.L. and H.B.E. Data analysis and interpretation was performed by H.B.E., K.J.G., S.D.K., P.P. and J.J.S. Drafting and revision of the article was conducted by K.J.G., S.D.K., W.-K.L. and J.J.S.
Supplementary material available online at http://jeb.biologists.org/cgi/content/full/216/12/2293/DC1
No competing interests declared.
This work was supported by the National Science Foundation [EPS-0447679, IOS-0953297 to K.J.G. and EFRI-0938047 to J.J.S.], the National Institutes of Health (NIH) National Center for Research Resources [2P20RR0l5566 to K.J.G.] and the Institute for Critical Technology and Applied Science [118130 to J.J.S.]. The contents of this study are solely the responsibility of the authors and do not necessarily reflect the views of the NIH. Use of the Advanced Photon Source at Argonne National Laboratory was supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences [DE-AC02-06CH11357]. Deposited in PMC for release after 12 months.
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