Diapause: Definition, Phases, Examples

Diapause is a condition when most of the life processes are shut down due to unfavorable conditions. This type of condition is most commonly observed in insects(most commonly arthropods) and some selected groups of invertebrates. Let us learn in detail about the condition Diapause now.

Keyterms: Insects, Arthropods, Invertebrates, Diapause, Snails, Crustaceans, Embryonic stages, Embryo phase

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Diapause: Definition

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The physiological state of dormancy or developmental arrest where most life processes are shut down in case of any animal is called diapause. 

This occurs during unfavourable conditions and is most commonly observed in insects, especially in arthropods. The diapause can happen at any stage during the life cycle of an insect such as embryonic, larval, pupal, and active adult stage. It is a spontaneous response amongst these animals. 

Adverse environmental conditions like shortage of food, changes in day length and temperature, etc. are usually the primary cause of diapause in insects. In these conditions, the concentration of growth hormones in their body decreases, and thus, developmental halt sets in.

When this physiological interruption occurs during the pupae stage of insects like cocoons of moths, any physiological development slows to a halt. But, in an adult and active stage, feeding habits or reproductive behaviour is halted or slowed down.

Though diapause indicates that it is a genetic phenomenon, it can be removed experimentally by providing favourable surrounding conditions for the growth of the animals.

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Organisms Exhibiting Diapause

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• Diapause is exhibited by several mites and insects, and a few snails and crustaceans. This developmental arrest is also shown by some other certain groups of animals. 
• The longest ever diapause to be reported was that of a moth named Prodoxus Y-inversus, which is found in the United States and South Western New Mexico and can remain dormant for as long as 19 years. 
• Several arthropods like southwestern corn borer, tobacco hornworm, and flesh fly are shown to go through the diapause stage during their embryological stage. 
• Diapause is observed in the silkworm between its late larval and late embryonic stages. 
• In fishes, a species called mummichog features dormancy in the embryo phase.

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Phases of Diapause in Insects

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Diapause is a developmental suspension in many animals during any stage of their life cycle due to harsh natural conditions. Some of the distinct phases of diapause observed in insects are given below:

• Induction: 

  • This stage occurs before the beginning of unfavourable environmental cues. Essentially the onset of harsh conditions can trigger such a response. 
  • Certain environmental stimuli called token stimuli, trigger the diapause behaviour in the animals. 
  • These stimuli themselves do not have any negative impact on the environment but helps the insects to forecast an impending transformation in the environmental conditions.
• Preparation: 
  • In this phase, insects prepare their bodies for the life process suspension. 
  • It is characterized by the insects storing molecules of metabolic resources such as carbohydrates, proteins, and lipids to sustain themselves during the diapause. 
  • This phase signifies the beginning of the change in body processes to survive the long-dormant stage.
• Initiation: 
  • This process is the most important phase to begin diapause. 
  • It is characterized by the spontaneous termination of morphological development in insects. 
  • The cessation includes a colour change, moulting into a diapause stage, or the release of special enzymes.
• Maintenance: 
  • In this phase, the metabolism gets reduced and embryological development is arrested. 
  • Moreover, sensitivity to certain stimuli is increased, especially the ones that can prevent the termination of the diapause.
• Termination: 
  • This phase as the name suggests ends the developmental interruption. 
  • Nonetheless, some insects depend on certain environmental stimuli to trigger the termination of diapause.
• Post-Diapause Quiescence: 
  • It is the last stage. In this stage, a period of inactivity is seen in the insects. 
  • After which eventually they start resuming their physiological development if the environmental conditions are favourable.

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Types of Diapause

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There are mainly two types of diapause found in the animal world. They are as follows –

• Obligatory diapause: 
  • In this process, insects undergo diapause at the predetermined point in their life cycle, without the introduction of any stimuli like environmental factors. 
  • The process occurs in every generation. 
  • It is most commonly seen in univoltine insects, meaning insects that have one generation per year.
• Facultative diapause: 
  • In this process, the insects undergo diapause to ensure survival, when the environmental factor changes for the worse. 
  • It is most commonly seen in bivoltine (two generations per year) or multivoltine insects (more than two generations per year).

In addition to these, many insects also undergo reproductive diapause. In this process, the reproductive functions in adult insects are temporarily suspended. The monarch butterfly in North America is the best example of reproductive diapause.

Read More: Characteristics Of Organisms

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Environmental factors

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The three main environmental factors responsible for the onset of diapause are included here:

• Photoperiod
• Temperature
• Food

Besides these, other factors such as a change in pH, the salinity of the soil, moisture, and scarcity of other life-sustaining resources can also induce the diapause process in animals. It must be noted that no single factor influences diapause; rather the combined influence of all the factors, along with programmed genetic factors, controls the mechanisms of diapause.

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Difference between Hibernation and Diapause

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Diapause is vastly different from hibernation. Unlike hibernation, diapause does not occur because of the onset of the cold weather. Hibernation is a seasonal activity whereas diapause happens, owing to adverse environmental conditions like scarcity of food, changes in temperature, etc. Mostly arthropods and a select group of vertebrates show this temporary developmental halt in any stage of their life cycle.

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Things to Remember

• Diapause is a condition when most of the life processes are shut down due to unfavorable conditions.
• Diapause is most commonly observed in insects (most commonly arthropods) and in some invertebrates.
• The longest ever diapause to be reported was that of a moth named Prodoxus Y-inversus, which is found in the United States and South Western New Mexico and can remain dormant for as long as 19 years.
• Phases of Diapause in insects include:
  • Induction
  • Preparation
  • Initiation
  • Maintenance
  • Termination
  • Post-Diapause Quiescence
• Diapause can be broadly classified into 2 types:
  • Obligatory
  • Facultative
• Diapause is ]different from hibernation. 
• Unlike hibernation, diapause does not occur because of the onset of the cold weather.

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