Dauer Formation Induced by High Temperatures in Caenorhabditis elegans

Dauer formation in Caenorhabditis elegans is regulated by several environmental stimuli, including a pheromone and temperature. Dauer formation is moderately induced as the growth temperature increases from 15° to 25°. Here we show that dauer formation is very strongly induced at a temperature of 27° in both wild-type animals and mutants such as unc-64, unc-31, and unc-3, which do not form dauers at 25°. A 27° temperature stimulus is sufficient to induce dauer formation in wild-type animals independent of pheromone. Analysis of previously described dauer mutants at 27° reveals a number of surprising results. Several classes of mutants (dyf, daf-3, tax-4, and tax-2) that are defective in dauer formation at lower temperatures reverse their phenotypes at 27° and form dauers constitutively. Epistasis experiments place unc-64 and unc-31 at a different position in the dauer pathway from unc-3. We also uncover new branches of the dauer pathway at 27° that are not detected at 25°. We show that epistatic gene interactions can show both quantitative and qualitative differences depending on environmental conditions. Finally, we discuss some of the possible ecological implications of dauer induction by high temperatures.