Diapause

Source: Wikipedia, the free encyclopedia.

In animal

physiological state with very specific initiating and inhibiting conditions. The mechanism is a means of surviving predictable, unfavorable environmental conditions, such as temperature extremes, drought, or reduced food availability. Diapause is observed in all the life stages of arthropods, especially insects
.

Activity levels of diapausing stages can vary considerably among species. Diapause may occur in a completely immobile stage, such as the

pupae and eggs, or it may occur in very active stages that undergo extensive migrations, such as the adult monarch butterfly
, Danaus plexippus. In cases where the insect remains active, feeding is reduced and reproductive development is slowed or halted.

Embryonic diapause, a somewhat similar phenomenon, occurs in over 130 species of mammals, possibly even in humans,[3] and in the embryos of many of the oviparous species of fish in the order Cyprinodontiformes.[4]

Phases of insect diapause

Diapause in insects is a dynamic process consisting of several distinct phases. While diapause varies considerably from one taxon of insects to another, these phases can be characterized by particular sets of metabolic processes and responsiveness of the insect to certain environmental stimuli.[5] For example, Sepsis cynipsea flies primarily use temperature to determine when to enter diapause.[6] Diapause can occur during any stage of development in arthropods, but each species exhibits diapause in specific phases of development. Reduced oxygen consumption is typical as is reduced movement and feeding.[7] In Polistes exclamans, a social wasp, only the queen is said to be able to undergo diapause.[8]

Comparison of diapause periods

The sensitive stage is the period when stimulus must occur to trigger diapause in the organism. Examples of sensitive stage/diapause periods in various insects:[9]

Scientific name Common name Sensitive stage Diapause
Diatraea grandiosella Southwestern corn borer early larval late larval[10]
Sarcophaga crassipalpis Flesh fly early larval pupa
Sarcophaga argyrostoma Flesh fly mid to late larval pupa
Manduca sexta Tobacco hornworm late embryonic (egg) to late larval pupa
Leptinotarsa decemlineata
Colorado potato beetle early adult late adult
Bombyx mori Silkworm late embryonic (egg) to early larval embryonic
Lymantria dispar
Spongy moth late embryonic late embryonic
Danaus plexippus
Monarch butterfly early adulthood adulthood
Acronicta rumicis Knott grass moth mid larval mid larval
Cydia pomonella Codling moth early to mid larval mid larval[11]
Gynaephora groenlandica Arctic woolly bear moth mid larval mid larval[12]
Cuterebra fontinella Mouse botfly mid larval pupa[13]

Induction

The induction phase occurs at a genetically predetermined stage of life, and occurs well in advance of the environmental stress.

allelochemicals from food plants. These stimuli are not in themselves favourable or unfavourable to development, but they herald an impending change in environmental conditions.[2]

Preparation

The preparation phase usually follows the induction phase, though insects may go directly from induction to initiation without a preparation phase.

hydrocarbons lining the puparium, effectively reducing the ability of water to cross the cuticle.[16]

Initiation

oyamel trees. One tree is completely covered in butterflies. These butterflies were located on a preserve outside of Angangueo, Michoacán, Mexico

Maintenance

During the maintenance phase, insects experience lowered metabolism and developmental arrest is maintained.[5] Sensitivity to certain stimuli which act to prevent termination of diapause, such as photoperiod and temperature, is increased. At this stage, insects are unresponsive to changes in the environment that will eventually trigger the end of diapause, but they grow more sensitive to these stimuli as time progresses.

Termination

In insects that undergo obligate diapause, termination may occur spontaneously, without any external stimuli.[5] In facultative diapausers, token stimuli must occur to terminate diapause. These stimuli may include chilling, freezing, or contact with water, depending on the environmental conditions being avoided. These stimuli are important in preventing the insect from terminating diapause too soon, for instance in response to warm weather in late fall. In the Edith's checkerspot butterfly, individuals must receive enough sunlight in order to terminate the diapause stage and become a fully grown butterfly.[18] Termination may occur at the height of unfavourable conditions, such as in the middle of winter. Over time, depth of diapause slowly decreases until direct development can resume, if conditions are favourable.

Post-diapause quiescence

Diapause frequently ends prior to the end of unfavourable conditions and is followed by a state of quiescence from which the insect can arouse and begin direct development, should conditions change to become more favourable.[5] This allows the insect to continue to withstand harsh conditions while being ready to take advantage of good conditions as soon as possible.

Regulation

Diapause in insects is regulated at several levels. Environmental stimuli interact with genetic pre-programming to affect

endocrine
pathways, and, eventually, metabolic and enzymatic changes.

Environmental

Environmental regulators of diapause generally display a characteristic

Indian mealmoth, where individuals diapause in different developmental stages due to environmental temperature.[20] Food availability and quality may also help regulate diapause. In the desert locust, Schistocerca gregaria, a plant hormone called gibberellin stimulates reproductive development.[21] During the dry season, when their food plants are in senescence
and lacking gibberellin, the locusts remain immature and their reproductive tracts do not develop.

Neuroendocrine

The neuroendocrine system of insects consists primarily of neurosecretory cells in the brain, the corpora cardiaca, corpora allata and the prothoracic glands.[2] There are several key hormones involved in the regulation of diapause: juvenile hormone (JH), diapause hormone (DH), and prothoracicotropic hormone (PTTH).[22]

Prothoracicotropic hormone stimulates the prothoracic glands to produce

ecdysteroids that are required to promote development.[22]
Larval and pupal diapauses are often regulated by an interruption of this connection, either by preventing release of prothoracicotropic hormone from the brain or by failure of the prothoracic glands to respond to prothoracicotropic hormone.

The corpora allata is responsible for the production of

Adult diapause is often associated with the absence of JH, while larval diapause is often associated with its presence.

In adults, absence of JH causes degeneration of flight

muscles and atrophy or cessation of development of reproductive tissues, and halts mating behaviour. The presence of JH in larvae may prevent moulting to the next larval instar, though successive stationary moults may still occur.[24] In the corn borer, Diatraea gradiosella, JH is required for the accumulation by the fat body of a storage protein that is associated with diapause.[25]

Diapause hormone regulates

eggs, which is converted into the polyhydric alcohols glycerol and sorbitol. Sorbitol directly inhibits the development of the embryos. Glycerol and sorbitol are reconverted into glycogen
at the termination of diapause.

Tropical diapause

Diapause in the

trees
may be more available following rainy seasons. Also, diapause may serve to synchronize mating seasons or reduce competition, rather than to avoid unfavourable climatic conditions.

Diapause in the tropics poses several challenges to insects that are not faced in

may still be abundant during the diapause period.

Aggregations are common among diapausing tropical insects, especially in the orders

Relative humidity is increased within the aggregations and beetles experience less water loss, probably due to decreased surface area to volume ratios reducing evaporative water loss.[28]

See also

Embryonic diapause

  • Eburia quadrigeminata, the species with the longest reported diapause among insects (up to 40 years).
  • Polygonia c-album, whose larvae exhibit density-dependent polymorphism where one of two morphs is a diapausing phase.

References

  1. , p 403.
  2. ^ a b c Tauber, M.J., Tauber, C.A., Masaki, S. (1986) Seasonal Adaptations of Insects. Oxford University Press[page needed]
  3. PMID 28928280
    .
  4. . Annual aplocheiloid killifish embryos possess a rare ability among vertebrates to enter stages of developmental arrest (diapause) when subjected to adverse environmental conditions.
  5. ^ .
  6. ^ Blanckenhorn, W. U. (1998). Altitudinal differentiation in the diapause response of two species of dung flies. Ecological Entomology 23, 1-8.
  7. , pp. 403–404
  8. .
  9. ^ , p 404.
  10. ^ Bulletin of Entomological Research (1976), 66:75–79 Cambridge University Press, Copyright © Cambridge University Press 1976, Diapause of the southwestern corn borer, Diatraea grandiosella Dyar (Lepidoptera, Pyralidae): effects of a juvenile hormone mimic: G. M. Chippendalea1 and C.-M. Yina1a1, Department of Entomology, University of Missouri, Columbia, Missouri 65201, U.S.A.
  11. ^ Tadic, M. (1957). The Biology of the Codling Moth as the Basis for Its Control. Univerzitet U Beogradu.
  12. ISSN
    0013-8738.
  13. ^ Scholl PJ (1991). "Gonotrophic Development in the Rodent Bot Fly Cuterebra fontinella (Diptera: Oestridae)". Journal of Medical Entomology. 28 (3): 474–476.
    PMID 1875379
    .
  14. ^ a b c Huffaker, C.B. and Gutierrez, A.P., Eds. 1999. Ecological Entomology. John Wiley & Sons, Inc.
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