- Dauer larva
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Dauer (German for "duration") describes an alternative developmental stage of nematode worms, particularly Caenorhabditis elegans whereby the larva goes into a type of stasis and can survive harsh conditions. It may also be equivalent to the infective stage of parasitic nematode larvae. The Dauer state is given other names in the various types of nematodes such as ‘diapause’ , ‘hyperbobis’, ‘spring rise’, but since the C. elegans nematode has become the most studied nematode, the term ‘dauer stage’ or 'dauer larvae' is becoming universally recognised when referring to this state in other nematodes.
Under environmental conditions that are favorable for reproduction, larvae develop through 4 stages or molts which are designated as L1, L2, L3 and L4. After L4, animals moult to the reproductive adult stage. However, when the environment is unfavorable, L1 and L2 animals have the option to divert their development from reproduction to dauer formation. Signals such as temperature, food supply, and a dauer-inducing pheromone (population density cue) influence this dauer decision. Dauer larvae are thus considered an alternative L3 stage larva, and this stage is sometimes referred to as L2d. L2d animals are also considered pre-dauer and are characterised by delayed development and dark intestines produced by storage of fat.
Dauer larvae are extensively studied by biologists because of their ability to survive harsh environments and live for extended periods of time. Dauer formation in C. elegans requires a nuclear receptor DAF-12 and a forkhead transcription factor DAF-16. In favorable environments, DAF-12 is activated by a steroid hormone, called Dafachronic Acid, produced by the cytochrome p450, DAF-9. Interestingly, DAF-9 and DAF-12 have been implicated by Cynthia Kenyon and colleagues as being required for extended longevity seen in animals that lack germlines.
A characteristic of the dauer stage is the pronounced alae which may be implicated in the entering (L1) and exiting (pre adult or L4 in C.elegans) of the dauer stage.
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