Dormancy

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As dormancy (from the Latin dormire = to sleep) are all forms of developmental retardation in living beings. These are partly due to external factors, but they can also be genetically and hormonally controlled. Above all, dormancy phases ensure that animals and plants survive in unfavorable environmental conditions.

The main characteristics of dormancy include a greatly reduced metabolism and increased resistance . The dormancy can occur in all development phases and also within the same species, depending on external conditions, can be of different lengths. B. can be observed at dormancy .

Dormancy in botany

Seed dormancy

With the term dormancy is in botany seed dormancy referred to in seeds premature germs to prevent under unfavorable conditions or even on the mother plant. This dormancy can be terminated prematurely by treating the seeds, known as stratification .

Bud rest

Annual cycle of sympodial growing orchids with resting phase after the formation of the new annual shoot, e.g. B. Miltonia or Odontoglossum
Annual cycle of sympodial growing orchids with resting phase after flowering, e.g. B. Cycnoches ventricosum , Dendrobium nobile or Laelia

The dormancy of plants is also referred to as the dormancy of the buds: Flower or side shoot buds can remain in a dormant phase for a long time due to external influences or hormonally controlled. The rest of the buds of the side shoots is particularly pronounced in many plant species, which is mediated by the main shoot or main shoot and is also referred to as apical dominance . If you remove the main shoot, the dormancy of the side shoots is broken and they begin to grow.

Dormancy also plays a major role in plants in temperate areas and regions further to the north: these plants are only able to sprout again after a certain period of time below a certain temperature. This is important insofar as such short-term warm phases in the cold season do not lead to the plant sprouting prematurely and then with a high probability of being severely damaged by the onset of frost again . The more southerly the original range of a plant species is, the lower the need for cold normally is to break the dormancy. This is the reason why, for example, almond trees in southern Germany sprout and bloom as early as December or January in warm winter phases.

Another example of dormancy in the plant kingdom are the rest periods of numerous sympodially growing orchids in adaptation to the respective regional cold and / or drought periods. The two figures above show the two most common dormancy patterns.

Dormancy in Zoology

Dormancy is a survival strategy that is mainly implemented by cold-blooded ( poikilothermal ) animals. It can affect not only the entire organism , but also only the gonads . In the case of eggs or embryos, the dormancy is triggered by the mother, in the case of parasitoids it is usually triggered by the hosts. The term diapause is often used synonymously, but always includes an endogenous component that changes the metabolism (diapause in the broader sense ), in contrast to the purely exogenously influenced quiescence.

There are two main forms of dormancy, with the trend going from consecutive to prospective dormancy. Furthermore, there is a tendency to limit dormancy to a developmental stage.

Consecutive dormancy

In this form, the change in external factors plays the main role. The development curve follows the change in the decisive external factor and can ultimately lead to a development standstill in suboptimal environmental conditions. The factor that triggers dormancy is also the one that ends dormancy. The following external factors occur here: temperature, food, humidity and photoperiod . The consecutive dormancy is divided into quiescence and oligopause, the latter being related to diapause i. w. S. heard.

Quiescence

In the case of quiescence, dormancy occurs immediately when the unfavorable begins and is also ended immediately after the unfavorable end. It can occur at any stage of development. The hibernation can be viewed as thermal quiescence of the homoiothermal animals.

Oligopause

In oligopause, dormancy occurs gradually after the onset of disfavor and after the stimulus has accumulated . It is “checked”, as it were, whether the unfavorable situation will persist in the long term or whether there is only a short-term environmental fluctuation. This is followed by a change in physiology . The oligopause is also gradually ended after the stimulus has decumulated . According to the stage at which the oligopause begins, three types are distinguished:

  1. Quiescitary oligopause: dormancy can occur at any stage of development.
  2. Typical oligopause: The sensitivity to the stimulus that triggers dormancy and its accumulation is differently pronounced in the developmental stages.
  3. Diapausal oligopause: The dormancy is clearly narrowed to certain stages of development.

The hibernation is thermal Oligopause the homoiothermen animals.

Prospective dormancy

In this form, the time of the dormancy is genetically determined and is so that the developmental change begins before a mostly seasonal change in an external factor takes place in an unfavorable range, so to speak foresight. The dormancy is linked to a certain stage of development. This dormancy also has two forms, both of which occur during diapause i. w. S. include:

Parapause

While in the other forms of dormancy the development comes to a standstill during unfavorable environmental conditions, here a development stage is set up for further development during the unfavorable and even requires this. This is why the parapause is mandatory and occurs when the certain stage is reached. The termination takes place only after reaching the next stage by an external factor. The main factors here are the temperature or the photoperiod.

Since all individuals of a population parapause at the same stage and are released from dormancy only once in the course of the year by the same external factor, the development of this population runs synchronously and there is only one generation per year ( monovoltinism ).

Eudiapause

This is the diapause ie the dormancy-triggering factor in the eudia pause is only the photoperiod , as it is astronomically precise and therefore always reliable, in contrast to the other external factors. The critical photoperiod is the ratio of light to dark hours at which half of a population begins to diapause and changes with increasing latitude . The signal for triggering the eudia pause must be given in the previous stage of development. If it does not happen, the intended stage experiences a nondiapausal development. Therefore the eudia pause is optional . The terminating external factor is the temperature: an obligatory, longer period of cold. If the eudia pause is over, although the environmental conditions are still unfavorable, quiescence follows.

The optional character of the eudia pause gives a species the opportunity to produce more than one generation per year (potential polyvoltinism ). For example, the map butterfly Araschnia levana has two generations per year, one of which undergoes a nondiapause development and the other eudia pause. This also leads to different phenotypes between the two generations ( seasonal diphänism ) of this species.

literature

Individual evidence

  1. ↑ Carpenter: Introduction to Ecology. 4th, greatly changed and expanded edition. 1993, p. 82 ff.