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First published online January 19, 2006
Journal of Experimental Biology 209, 466-474 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02024
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A comparative analysis of thermogenic capacity and cold tolerance in small birds

David L. Swanson* and Eric T. Liknes{dagger}

Department of Biology, University of South Dakota, 414 East Clark Street, Vermillion, SD 57069, USA


Figure 1
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  		Fig. 1. Phylogeny of bird species used in comparative analyses in this study. Tree topology and branch lengths represent genetic distances ({Delta}T50H values) from DNA/DNA hybridization data (Sibley and Ahlquist 1990Go). The total distance from the base node of the tree to the branch tips is 26.3 for the species in this study.

 

Figure 2
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  		Fig. 2. Regressions of logMsum (A) and logTCL (B) against logMb in summer (solid line) and winter (broken line). At both seasons, logMsum was significantly and positively associated with logMb and logTCL was significantly and negatively related to logMb. Winter equations were significantly elevated for logMsum and significantly lower for logTCL than summer equations, suggesting that winter increases in Msum are correlated with decreases in TCL. Msum, W; TCL, °K; Mb, g.

 

Figure 3
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  		Fig. 3. Residuals from logMsum vs logMb regressions plotted against residuals from logTCL vs logMb regressions. Residuals of logMsum were significantly and negatively associated with residuals of logTCL at both seasons, indicating a phenotypic correlation between Msum and TCL.

 

Figure 4
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  		Fig. 4. Residuals from logMsum contrasts vs logMb contrasts regressions plotted against residuals from logTCL contrasts vs logMb contrasts regressions. Residuals of logMsum contrasts were significantly and negatively associated with residuals of logTCL contrasts at both seasons, indicating a phenotypic correlation between Msum and TCL independent of both body mass and phylogeny.

 

Figure 5
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  		Fig. 5. Occurrence of high (solid bold lines) and low (broken lines) Msum for tips of phylogenies for summer and winter birds in this study. The numbers and letters at the ancestral nodes and branch tips refer to high Msum (1), low Msum (2), low TCL (good cold tolerance; A), high TCL (poor cold tolerance; B). Low and high Msum and TCL were determined from tips or nodes that fell outside of 95% confidence intervals from allometric regressions of logMsum and logTCL on logMb for both raw data and phylogenetically independent contrasts.

 




© The Company of Biologists Ltd 2006