Dauer larva
Encyclopedia
Dauer 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 larva
e. 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 germline
s.
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.
Nematode
The nematodes or roundworms are the most diverse phylum of pseudocoelomates, and one of the most diverse of all animals. Nematode species are very difficult to distinguish; over 28,000 have been described, of which over 16,000 are parasitic. It has been estimated that the total number of nematode...
worms, particularly Caenorhabditis elegans
Caenorhabditis elegans
Caenorhabditis elegans is a free-living, transparent nematode , about 1 mm in length, which lives in temperate soil environments. Research into the molecular and developmental biology of C. elegans was begun in 1974 by Sydney Brenner and it has since been used extensively as a model...
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 larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
e. 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
Ecdysis
Ecdysis is the moulting of the cuticula in many invertebrates. This process of moulting is the defining feature of the clade Ecdysozoa, comprising the arthropods, nematodes, velvet worms, horsehair worms, rotifers, tardigrades and Cephalorhyncha...
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
Temperature
Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...
, food supply, and a dauer-inducing pheromone
Pheromone
A pheromone is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting outside the body of the secreting individual to impact the behavior of the receiving individual...
(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
Transcription factor
In molecular biology and genetics, a transcription factor is a protein that binds to specific DNA sequences, thereby controlling the flow of genetic information from DNA to mRNA...
DAF-16. In favorable environments, DAF-12 is activated by a steroid
Steroid
A steroid is a type of organic compound that contains a characteristic arrangement of four cycloalkane rings that are joined to each other. Examples of steroids include the dietary fat cholesterol, the sex hormones estradiol and testosterone, and the anti-inflammatory drug dexamethasone.The core...
hormone
Hormone
A hormone is a chemical released by a cell or a gland in one part of the body that sends out messages that affect cells in other parts of the organism. Only a small amount of hormone is required to alter cell metabolism. In essence, it is a chemical messenger that transports a signal from one...
, 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 germline
Germline
In biology and genetics, the germline of a mature or developing individual is the line of germ cells that have genetic material that may be passed to a child.For example, gametes such as the sperm or the egg, are part of the germline...
s.
A characteristic of the dauer stage is the pronounced alae
Alae (anatomy)
The alae is a protruding ridge that forms longitudinally on many nematodes.In the Caenorhabditis elegans nematode they are present in the L1, dauer and adult stages. The alae is most pronounced during the dauer larval stage and not present in the L2, and L3 C...
which may be implicated in the entering (L1) and exiting (pre adult or L4 in C.elegans) of the dauer stage.