12 The Dauer Larva

Abstract

I. INTRODUCTION
The dauer, or “enduring,” larval stage of Caenorhabditis elegans is an example of facultative diapause. Environmental factors act as signals to a receptive developmental stage (the L1 larva), resulting in altered physiology and developmental potential that leads to formation of a third-stage larva specialized for dispersal and long-term survival. Dauer larvae are capable of active movement, but they do not feed. They have a unique morphology and resistance to stress, are altered in energy metabolism, and are arrested in development, as well as aging. Dauer larvae survive four to eight times the 3-week life span of animals that have bypassed the dauer stage. The dauer state itself has been considered to be nonaging, because the duration of the dauer stage does not affect postdauer life span (Klass and Hirsh 1976). As far as is known, the consumption of stored energy may be the major factor limiting dauer larva life expectancy.

Various forms of diapause are common among nematodes, and there may be interesting parallels between the C. elegans dauer larva and arrested developmental forms that have been documented as obligatory stages in the life cycles of a number of parasitic species (for review, see Michel 1974; Evans and Perry 1976). In many cases, these arrested stages are dispersal forms specialized to survive periods between host infections (Riddle and Bird 1985).

Dauer larvae exhibit behavior not observed in other stages. Pharyngeal pumping is completely suppressed, and the larvae often lie motionless. Although lethargic, they do show a negative response...