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First published online August 17, 2007
Journal of Experimental Biology 210, 3107-3116 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.007351

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Thermal preference of Caenorhabditis elegans: a null model and empirical tests

Jennifer L. Anderson¹, Lori Albergotti^1,*, Stephen Proulx², Colin Peden¹, Raymond B. Huey³ and Patrick C. Phillips^1,

¹ Center for Ecology and Evolutionary Biology, University of Oregon, Eugene, OR 97402, USA
² Department of Ecology, Evolution and Organismal Biology, Iowa State University, Ames, IA 50011, USA
³ Department of Biology, University of Washington, Seattle, WA 98195, USA

Author for correspondence (e-mail: pphil{at}uoregon.edu)

Accepted 24 June 2007

The preferred body temperature of ectotherms is typically inferred from the observed distribution of body temperatures in a laboratory thermal gradient. For very small organisms, however, that observed distribution might misrepresent true thermal preferences. Tiny ectotherms have limited thermal inertia, and so their body temperature and speed of movement will vary with their position along the gradient. In order to separate the direct effects of body temperature on movement from actual preference behaviour on a thermal gradient, we generate a null model (i.e. of non-thermoregulating individuals) of the spatial distribution of ectotherms on a thermal gradient and test the model using parameter values estimated from the movement of nematodes (Caenorhabditis elegans) at fixed temperatures and on a thermal gradient. We show that the standard lab strain N2, which is widely used in thermal gradient studies, avoids high temperature but otherwise does not exhibit a clear thermal preference, whereas the Hawaiian natural isolate CB4856 shows a clear preference for cool temperatures (17°C). These differences are not influenced substantially by changes in the starting position of worms in the gradient, the natal temperature of individuals or the presence and physiological state of bacterial food. These results demonstrate the value of an explicit null model of thermal effects and highlight problems in the standard model of C. elegans thermotaxis, showing the value of using natural isolates for tests of complex natural behaviours.

Key words: Caenorhabditis elegans, diffusion model, natural variation, null model, thermal gradient, thermal preference

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