Quantitative analysis of thermotaxis in the nematode Caenorhabditis elegans

Thermotaxis (TTX) is one of the sophisticated behaviors in the nematode Caenorhabditis elegans. Although the mechanisms of thermotaxis have been deduced from different studies, they are controversial. Previous studies proposed a behavioral model where thermotaxis is regulated by the counterbalance between two opposite driving forces, while recent studies proposed stochastic models. In this study, we analyzed thermotaxis by a novel quantitative population TTX assay using a gentle linear thermal gradient. Analysis of thermotaxis in wild type animals revealed a clear thermal preference to a cultivation temperature with regard to the distribution of animals and the TTX mean expressing temperature preference. A time course assay revealed that the behavioral response to a preferred temperature was initially suppressed for at least 15 min in the animals cultivated at 23 degrees C, but not in those cultivated at 17 degrees C. Our result provides a possible explanation for the inconsistency between the various studies on thermotaxis and is consistent with the early behavioral model, where thermotaxis is regulated by the counterbalance between two driving forces.