Key Differences Between Diapause and Hibernation
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-
Induction
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.
Preparation
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.
Initiation
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.
Maintenance
By reducing metabolism and suspending embryological development, the maintenance phase occurs. Moreover, certain environmental stimuli trigger the sensitivity that can prevent diapause termination.
Termination
The termination phase ends the developmental interruption. Nonetheless, some insects depend on certain environmental stimuli that help the termination phase to set in.
Post-Diapause Quiescence
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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FAQs on Diapause Explained: Meaning, Stages & Comparison
1. What is diapause, as explained in the CBSE Class 12 syllabus?
In the context of the CBSE Class 12 syllabus on Organisms and Populations, diapause is defined as a stage of suspended development that certain organisms enter to survive unfavourable environmental conditions. It is a genetically programmed, hormonally controlled state of dormancy where metabolic activity is significantly reduced. A common example is the diapause stage in many zooplankton species in lakes and ponds during winter.
2. What are the main environmental factors that trigger diapause?
Diapause is typically initiated by predictive environmental cues that signal the onset of future adverse conditions, rather than the conditions themselves. The primary triggers include:
- Photoperiod: Changes in the length of day and night are the most reliable cues for seasonal change.
- Temperature: A consistent drop or rise in temperature can signal the start of winter or summer.
- Food Availability: A scarcity of food resources can trigger a state of developmental arrest to conserve energy.
- Moisture and pH: Changes in water availability or soil/water pH can also act as triggers in some species.
3. How does diapause fundamentally differ from hibernation and aestivation?
While all three are forms of dormancy, they differ significantly in their mechanism and control. Diapause is a pre-programmed developmental arrest controlled by hormones and is often initiated by predictive cues like day length, well before conditions become harsh. Hibernation (winter sleep) and aestivation (summer sleep) are more direct responses to existing extreme temperatures (cold or heat) and food scarcity, and are typically seen in vertebrates. Diapause can occur at any life stage (egg, larva, pupa, adult), whereas hibernation and aestivation are primarily adult phenomena.
4. What is the difference between obligate and facultative diapause?
The distinction lies in the genetic and environmental control of the process.
- Obligate Diapause: This type of diapause is genetically determined and occurs at a specific point in the life cycle of every generation, regardless of the environmental conditions. It is a fixed part of the organism's development.
- Facultative Diapause: This is an optional response that is triggered only when specific environmental cues signal impending harsh conditions. Organisms with facultative diapause will continue to develop normally if the environment remains favourable.
5. At which life stages can diapause occur? Provide examples.
Diapause is remarkable for its ability to occur at various stages of an organism's life cycle, depending on the species. Examples include:
- Egg Diapause: The silkworm, Bombyx mori, overwinters in the egg stage.
- Larval Diapause: The codling moth, a pest of apples, undergoes diapause in its late larval stage.
- Pupal Diapause: Many butterflies and moths, like the cabbage white butterfly, overwinter as pupae.
- Adult Diapause: The adult mosquito Culex pipiens enters reproductive diapause to survive the winter.
6. What is the ecological importance of diapause for a species?
The ecological importance of diapause is immense for species survival and population stability. It allows organisms to:
- Survive Predictable Hardships: It helps populations endure harsh seasonal conditions like extreme cold, heat, or drought.
- Synchronise Life Cycles: It ensures that organisms emerge as adults when resources, such as food plants or hosts, are most abundant.
- Avoid Competition: By staggering development, it can reduce competition for resources among individuals of the same species.
- Facilitate Dispersal: Dormant stages like eggs can be transported over long distances, aiding in species dispersal.
7. Can humans undergo diapause or a similar form of dormancy?
No, humans do not undergo diapause or hibernation. While we make behavioural adaptations to survive cold winters (e.g., wearing heavy clothing, using heating), we lack the physiological mechanism for entering a state of suspended animation or significantly reduced metabolism. Some recent research has explored a phenomenon called 'embryonic diapause' where a fertilised embryo's implantation can be delayed, but this is a highly specialised reproductive process and not a whole-body dormancy like that seen in insects or bears.
8. What is 'reproductive diapause' in adult insects?
Reproductive diapause is a specific type of diapause that occurs in the adult stage of an organism. During this period, the development of reproductive organs is halted, and mating or egg-laying activities cease. This allows the adult insect to conserve energy and survive through an unfavourable season. Once favourable conditions return, reproductive development resumes. This strategy is common in insects like the monarch butterfly during its migration and certain species of mosquitoes during winter.
