25 Chemotaxis and Thermotaxis

Abstract

I. INTRODUCTION
Chemosensation and thermosensation are two important sensory mechanisms that Caenorhabditis elegans uses to interact with its environment. Behavioral and genetic similarities between chemotaxis and thermotaxis indicate that these two types of tracking behaviors share molecular and cellular components.

C. elegans modifies many aspects of its behavior on the basis of chemical cues. Bacteria (its food) or bacterial metabolites stimulate feeding, defecation, and egg laying (Horvitz et al. 1982; Avery and Horvitz 1990; Thomas 1990; Avery and Thomas, this volume). The chemosensory system also detects a pheromone that regulates entry into the alternative dauer larva stage (see Riddle, this volume). Other pheromones contribute to mating between males and hermaphrodites (see Emmons and Sternberg, this volume). This chapter focuses on chemotaxis, the migration of animals toward bacteria (their food) or defined chemicals (Ward 1973; Dusenbery 1974).

Temperature is a major determinant of the animal’s metabolism. As a cold-blooded animal, C. elegans has a limited temperature range (~12–26°C) at which it is viable and fertile. Thermotaxis behaviors allow animals to track to a preferred temperature (see Hedgecock and Russell 1975).

II. C. ELEGANS RESPONDS TO A VARIETY OF CHEMICALS
In the soil, C. elegans lives at an air-water interface and is exposed to both liquid and airborne chemicals. It detects most water-soluble attractants in the micromolar concentration range (Ward 1973; Dusenbery 1980a) and volatile molecules in the picomolar concentration range (B. Terrill and D. Dusenbery, pers. comm.). Volatile molecules travel quickly through diffusion and turbulence in the air, whereas water-soluble...