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First published online July 20, 2007
Journal of Experimental Biology 210, 2649-2656 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.003350

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Critical thermal maxima in knockdown-selected Drosophila: are thermal endpoints correlated?

Donna G. Folk^*, Luke A. Hoekstra and George W. Gilchrist

Department of Biology, College of William and Mary, Williamsburg, VA 23187, USA

^* Author for correspondence (e-mail: dgfolk{at}roadrunner.com)

Accepted 2 May 2007

To explore the correlation of traits linked to thermotolerance, we compared three thermal endpoints (knockdown temperature and two critical thermal maxima) among replicate populations of Drosophila melanogaster selected for high, or low, knockdown temperature. The high knockdown flies maintain normal posture and locomotor ability within a knockdown column at temperatures 40°C, whereas the low knockdown flies fall out of the column at much cooler temperatures (35°C, on average). The critical thermal maximum (CT_max) for respiratory control in the selected knockdown populations was determined by analyzing CO₂ output of individuals during exposure to a temperature ramp (from 30°C to >45°C) and was indicated by an abrupt alteration in the pattern of CO₂ release. The CT_max for locomotor function was determined by monitoring activity (concurrent with CO₂ analysis) during the temperature ramp and was marked by the abrupt cessation of activity. We hypothesized that selection for high knockdown temperature may cause an upward shift in CT_max, whereas selection for low knockdown may lower CT_max. Correlations among the three thermal endpoints varied between the high and low knockdown flies. Finally, we compared metabolic profiles, as well as Q₁₀ values, among the high and low knockdown males and females during the temperature ramp.

Key words: Drosophila melanogaster, laboratory selection, thermotolerance, knockdown, critical thermal maximum, thermolimit respirometry, metabolic rate, Q₁₀