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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

View larger version (12K): [in this window] [in a new window]   Fig. 1. A diagram depicting the history of the original and newly established High TKD and Low TKD selection lines and the Control lines (from Folk et al., 2006).

View larger version (15K): [in this window] [in a new window]   Fig. 2. Thermolimit respirometry and activity data from a single fly during a temperature ramp. The CO2 output profile (in black) and the activity tracing (in red) of an LN male are shown. The black arrow indicates CTmax for spiracular control, whereas the red arrow indicates CTmax for locomotor function. The respirometry tracing shows the typical phases seen in other insect species: (A) exponential phase, (B) plateau, (C) mortal fall and (D) postmortal peak.

View larger version (9K): [in this window] [in a new window]   Fig. 3. Boxplots showing CTmax statistics for (A) locomotor function and (B) spiracular control in the HN, LN and CN flies (N=16 for each group). The horizontal line within each box indicates the median response, whereas the box outline denotes the range for the middle 50% of the data. The `whiskers' show the dispersion of the data (i.e. 1.5 times the interquartile range). Points beyond this range are shown as open circles. CTmax for locomotor function or spiracular control did not differ significantly among the groups. The Low TKD flies had a significant reduction in the variance for CTmax for locomotor function (P=2.257x10-5).

View larger version (6K): [in this window] [in a new window]   Fig. 4. CTmax for locomotor function is predictive of CTmax for spiracular control in the HN and CN groups. The slopes of the regressions were 0.99 (HN) and 1.04 (CN). The slope for the LN group was not significantly different from zero, due probably to the extreme lack of variability among the CTmax endpoints. The red symbols and line, HN values; blue, LN; black, CN. N=16 for each group.

View larger version (7K): [in this window] [in a new window]   Fig. 5. Metabolic profiles of the HN (red), LN (blue), and CN (black) males (broken lines) and females (solid lines) during a temperature ramp, ending at CTmax for locomotor function (N=8 for each group). Knockdown selection treatment did not affect significantly the mass-specific CO2 over the experimental range of temperatures (P=1.000), whereas sex had a strong effect (P=1.042x10-6). Specifically, males had a higher mass-specific CO2 throughout the experiment.

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