Genetic and Environmental Regulation of Dauer Larva Development

I. INTRODUCTION Dauer larvae were first identified as a special larval stage of insect-parasitic nematodes. These larvae, which differed structurally from all other stages of the same species, were termed “dauerlarven” by Fuchs (1915). The dauer (enduring) stage of Caenorhabditis elegans is formed when environmental conditions are inadequate for successful reproduction. In abundant food, the animal develops continuously through the four larval stages (L1–L4) to the adult. Coincident with increased population density and limited food supply, development is arrested at the second molt, and the third-stage larva that is formed is structurally and behaviorally specialized for dispersal and long-term survival (Cassada and Russell 1975). Dauer larvae do not feed, but they can survive at least four to eight times the normal 2-week life span of C. elegans (Klass and Hirsh 1976). When favorable conditions are encountered, the dauer larva begins to feed and resumes development to the adult. Both entry into and exit from the dauer stage are developmental responses to specific chemosensory cues. These cues inform the larva whether there will be sufficient food available to support its reproduction. The environmental cues are first assessed and integrated throughout the L1 stage (Golden and Riddle 1984b). The primary cue is a Caenorhabditis-specific pheromone constitutively released by the nematodes (Golden and Riddle 1984c). The pheromone is very stable and hydrophobic and has chromatographic properties similar to those of hydroxylated fatty acids and bile acids. The concentration of pheromone reflects nematode population density. Temperature and food modulate the response to pheromone...