[Biology Class Notes] on Diapause Pdf

Diapause meaning is a physiological state found mostly in arthropods. In this state, developmental arrest or dormancy is seen that signifies shutting down of most life processes. During the life cycle of an insect, diapause can happen at any stage such as embryonic, larval, pupal, and adult. 

This developmental arrest is a spontaneous response amongst these animals to survive unfavourable environmental conditions.

However, this dormancy occurs majorly in the pupae stage of insects like cocoons of moths. Diapause during the pupil stage slows any physiological development to a halt. But, in an adult and active stage, the reproductive process or feeding habit halts or slows down.

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

So, even though diapause meaning indicates that it is a genetic phenomenon, it can be removed experimentally by providing favourable conditions to the animals. 

Diapause and Hibernation

Animals living on the earth have come into existence after many years of evolution and adaptation. All the organisms have developed special features according to the environment they live in to sustain their life. It is very interesting to observe the various physiological and meta morphological characteristics and mechanisms that they manage to perform in different circumstances to sustain their lives and propagate. Some examples of physiological adaptation are gills in fish that help in extracting oxygen from the water they live in or the flapping pads in the feet of some amphibian frogs that help them in moving in the water. 

Apart from such modifications in organs or their specialisation for carrying out any specific functions, organisms also show typical modifications in their behaviour in response to the surroundings. The environment in the habitat of almost every organism is never constant but changes due to many planetary processes. If the environment becomes adverse for any organism, particularly arthropods then it is observed that they stop their growth process and divert all of their energy to protect themselves from the unfavourable conditions. This state of organisms is known as diapause. Adverse conditions can be anything like a severe cold or hot climate, or it can be sometimes the unavailability of essential resources such as food, water, light or nutrition. Though diapause is an involuntary action related to the genetic structure of an organism but can be controlled by manipulating the available environment.

Another type of inactivity is often observed in various organisms, particularly among bigger warm-blooded animals that are known as hibernation.  In this state, animals decrease their rate of metabolic activities such as body temperature, heart rate etc. This mainly happens during the winter season. Bears, groundhogs, hedgehogs and squirrels are examples of some such animals that adopt this mechanism to sustain in the winter season when there is a significant decrease in the availability of temperature, light and food. In general, they search for a suitable place for rest and conserve their energy through a long sleep for the whole months of the winter. 

Organisms that Show Diapause

Several mites and insects, and a few snails and crustaceans exhibit diapauses. This developmental arrest is a spontaneous response of these animals to unfavourable environmental conditions. Some certain groups of animals also exhibit diapauses.

A moth named Prodoxus Y-inversus can stay dormant for about 19 years. This is recorded as the longest diapause in biological science. This moth is seen in southwestern Mexico and the United States.

Diapause in the embryological stage is observed in several arthropods like southwestern corn borer, tobacco hornworm, and flesh fly.

A species of fish, mummichog also features dormancy in the embryo phase. The silkworm shows diapauses between its late larval and late embryonic stage.

 

Phases of Diapause in Insects

Diapause meaning is a developmental suspension in insects during any stage of their life cycle. Following stages can be found in an insect’s diapauses-

The induction stage happens before the beginning of unfavourable environmental cues. These specific environmental stimuli are known as “token stimuli” that starts the diapauses in insects. However, the stimuli don’t adversely impact any environmental conditions but help the animals to forecast impending environmental transformations. 

As the name suggests, during the preparation stage, insects prepare their bodies for the life process suspension. This phase comes right after the induction phase. Insects start reserving metabolic sources like carbohydrates, lipids, and protein to survive during the diapauses.

The initiation process is the most important phase to begin diapause. During this stage, the insects spontaneously terminate morphological development. The cessation includes releasing special enzymes, changing colour, etc.

Example: The firebugs generate some chemicals that help them to reduce the freezing point.

By reducing metabolism and suspending embryological development, the maintenance phase occurs. Moreover, certain environmental stimuli trigger the sensitivity that can prevent diapause termination.

The termination phase ends the developmental interruption. Nonetheless, some insects depend on certain environmental stimuli that help the termination phase to set in.

After the termination of diapause, a phase of inactivity or quiescence occurs in insects. During this stage, the insects eventually start resuming their physiological development, if the environmental conditions are favourable.

 

Difference between Hibernation and Diapause

Hibernation implies the seasonal inactivity that is seen in endotherms. By lowering heart rate, metabolic rate, body temperature, etc. some animals stay inactive during the winter season. Animals like groundhogs, hedgehogs, squirrels, etc. exhibit hibernation.

Diapauses occur because of the onset of adverse environmental conditions like scarcity of food, changes in temperature, etc. Mostly arthropods show this developmental halt during any stage of their life cycle.

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