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Hypoxia 2009 Speakers
Scott Kirkton
Department of Biological Sciences, Union College, Schenectady, NY
Email: scott.kirkton@gmail.com
Talk Title: Tracheal ventilation
Session: Hypoxic Responses: Insights from Insects
Abstract: Fossilized insect specimens from the late Paleozoic Era (approximately 250 million years ago) were significantly larger than related extant species. Geologic estimates suggest that atmospheric oxygen in the late Paleozoic Era was 35%. These findings have led to a prominent hypothesis that insect body size may be limited by oxygen delivery. Empirical evidence from developing Schistocerca americana grasshopper experiments supports this hypothesis. Previous researchers have shown that larger S. americana grasshoppers have a greater tidal volume at rest and double their tidal volume in hypoxia as compared to smaller animals. Our lab has shown that during jumping, larger S. americana grasshoppers have increased fatigue rates and a greater reliance on anaerobic metabolism. In addition by using electron paramagnetic resonance, we have demonstrated that the femoral oxygen stores are significantly depleted during the on-set of jumping in adult S. americana grasshoppers. If larger S. americana grasshoppers are more oxygen sensitive, do they then invest more energy in their tracheal system? Our previous electron microscopy work has shown that larger S. americana grasshoppers have significantly more tracheoles in their jumping muscle. However to determine whether larger grasshoppers also have more tracheal structures throughout their body, we are using phase contrast synchrotron x-ray imagining to quantify tracheal structure and function. This exciting technique allows the tracheal structures to be observed in living insects with no apparent side effects. Larger S. americana grasshoppers have proportionally more respiratory structures throughout their body (whole body tracheae and air sacs) than smaller animals (p<0.05). While the increased proportion of air sacs improve convective oxygen delivery in larger grasshoppers, the greater relative amount of body mass dedicated to respiratory structures may inhibit overall insect body size by reducing the amount of energy or space dedicated to other tissues.

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