Pheromone, food, and temperature : environmental cues controlling development of the Caenorhabditis elegans Dauer larva
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Development of the Caenorhabditis elegans dauer larva is influenced by the relative strengths of at least three environmental cues: a pheromone, food, and temperature. The fatty acid like pheromone enhances dauer larva forma�tion and inhibits recovery, and its concentration apparently serves as a measure of the population density. A labile, hydrophillic food-signal has effects opposite those of the pheromone, and its concentration provides a measure of the food-supply. The cues have been used in the analysis of dauer larva formation and recovery of the wild-type strain N2 and mutants affected in dauer larva formation. Dauer-inducing conditions produce a prolongation of the second intermolt period and morphologically distinguishable second stage larvae, called L2d. Unlike L2 larvae, L2d larvae have the potential to form either L3 or dauer larvae, depending on the environmental cues. Worms become committed to non-dauer development around the LI molt when grown in the absence of exogenous pheromone. Commitment to dauer larva formation occurs just before the second molt, at which time a few worms complete development into dauer larvae even if transfered to fresh medium. Incubation temperatures above 20�C enhance wild-type dauer larva formation in the presence of added pheromone, and temperature-shift studies place the temperature-sensitive period around the first molt. Some dauer-constitutive mutants overrespond to the pheromone, and apparently enhance the expression of the wild-type temperature-sensitive process. Two temperature-sensitive dauer-constitutive alleles, daf-4(m72) and daf-7(m62), are suppressed by the amber suppressors up-7(st5), indicating they are nonsense alleles and presumably produce a nonfunctional, rather than temperature-sensitive, gene product.
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