How and why Caenorhabditis elegans uses distinct escape and avoidance regimes to minimize exposure to noxious heat

Abstract

M inimizing the exposure to del- eterious extremes of temperature is essential for animals to avoid tissue damages. Because their body tempera- ture equilibrates very rapidly with their surroundings, small invertebrates are particularly vulnerable to the deleteri- ous impact of high temperatures, which jeopardizes their growth, fertility, and survival. The present article reviews recent analyses of Caenorhabditis elegans behavior in temperature gradients cov- ering innocuous and noxious tempera- tures. These analyses have highlighted that worm uses two separate, multi- componential navigational strategies: an avoidance strategy, aiming at staying away from noxious heat, and an escape strategy, aiming at running away after exposure. Here, I explain why efficient escape and avoidance mechanisms are mutually exclusive and why worm needs to switch between distinct behavioral regimes to achieve efficient protective thermoregulation. Collectively, these findings reveal some largely unrecog- nized strategies improving worm goal- directed navigation and the fascinating level of sophistication of the behav- ioral responses deployed to minimize the exposure to noxious heat. Because switching between avoidance and escape regimes circumvents constraints that are valid for navigation behaviors in general, similar solutions might be used by worms and also other organisms in response to various environmental parameters cov- ering an innocuous/noxious, non-toxic/ toxic range.