is a period in an organism's life cycle
when growth, development, and (in animals) physical activity is temporarily suspended. This minimizes metabolic activity
and therefore helps an organism to conserve energy
. Dormancy tends to be closely associated with environmental conditions
. Organisms can synchronize entry to a dormant phase with their environment
through predictive or consequential means. Predictive dormancy
occurs when an organism enters a dormant phase before
the onset of adverse conditions. For example, photoperiod
and decreasing temperature
are used by many plants
to predict the onset of winter
. Consequential dormancy
occurs when organisms enter a dormant phase after
adverse conditions have arisen. This is commonly found in areas with an unpredictable climate. While very sudden changes in conditions may lead to a high mortality rate
among animals relying on consequential dormancy, its use can be advantageous, as organisms remain active longer, and are therefore able to make greater use of available resources.
The most famous type of dormancy is hibernation, although most people use the term wrongly. Most people believe that bears hibernate. Bears do not hibernate. In fact there are very few mammals that do. Bears simply sleep the winter away, and there is a difference between that and true hibernation.
To explain the difference take the example of a true hibernator, a chipmunk. When a chipmunk enters hibernation its breathing slows from about 95 breaths per minute to one breath every 2 or 3 minutes. A chipmunk's body temperature also decreases from around 99°F to around 39°F, and its heart rate also drops drastically. All this slowing down of the system greatly reduces the amount of energy necessary for a chipmunk to survive, and this allows a chipmunk to overwinter on nothing but built up fat stores.
Bears, on the other hand, simply sleep the winter away. Their system does not slow down much more than it does in normal sleep. Bears will get up during the winter and hunt for food on occasion. Most females, in fact, wake up at least once during the winter. That is when they give birth. As soon as the cubs are born, they immediately suckle the mother and then they all go back to sleep.
There is one other important difference between sleeping and true hibernation. True hibernators, such as the chipmunk, are very hard to arouse from their dormant states. Bears, on the other hand, are easily aroused.
Hibernation is a mechanism in many animals to escape cold weather and food shortage over the winter. Hibernation may be predictive or consequential. An animal prepares for hibernation by building up a thick layer of body fat during late summer and autumn which will provide it with energy during the dormant period. During hibernation the animal undergoes many physiological changes, including decreased heart rate (by as much as 95%) and decreased body temperature. Animals that hibernate include bats, ground squirrels and other rodents, mouse lemurs, the European Hedgehog and other insectivores, monotremes and marsupials.
is a predictive strategy that is predetermined by an animal's genotype
. Diapause is common in insects
, allowing them to suspend development between autumn
, and in mammals
such as the red deer
, where a delay in attachment of the embryo
to the uterine
lining ensures that offspring
are born in spring, when conditions are most favorable.
, also spelled estivation
, is an example of consequential dormancy in response to very hot or dry conditions. It is common in invertebrates
such as the garden snail
but also occurs in other animals such as the lungfish
. The period of dormancy that bears experience during the winter is also called aestivation.
is an example of dormancy in reptiles
that is similar to hibernation
. It differs from hibernation in the metabolic processes involved.
is a short-term reduction of body temperature to an ambient level during periods of inactivity, often lasting only a few hours. Animals that experience torpor include small birds
such as hummingbirds
and some small mammals
such as bats
produce metabolically inactive forms that can survive intensely adverse conditions unharmed; these are known as cysts
. This is a consequential strategy. Inactivating these resistant forms is usually done using an autoclave
(pressurized heating device).
of the family Herpesvirus
are notable for remaining dormant within cells
in the human body. See for example varicella zoster virus
, which in an individual causes first chickenpox
then shingles (herpes zoster
). Concerning viruses this dormancy is often referred to as latency
or a latent
produces a latent infection in lymphocytes, and at this stage in its life-cycle it is called a provirus
This should not be confused with clinical latency.
In plant physiology
, dormancy is a period of arrested plant growth. It is a survival strategy exhibited by many plant species
, which enables them to survive in climates
where part of the year is unsuitable for growth, such as winter
or dry seasons
Plant species that exhibit dormancy have a biological clock that tells them to slow activity and to prepare soft tissues for a period of freezing temperatures or water shortage. After a normal growing season, dormancy can be brought on by decreasing temperatures, shortened day length, or a reduction in rainfall.
When a mature seed
is placed under favorable conditions and fails to germinate
, it is said to be dormant. There are two basic types of seed dormancy. The first is called seed coat dormancy
or external dormancy
, and is caused by the presence of a hard seed covering or seed coat
that prevents water and oxygen from reaching and activating the embryo
. The second type of seed dormancy is called embryo dormancy
or internal dormancy
, and is caused by a condition of the embryo which prevents germination
(Black M, Butler J, Hughes M. 1987). The oldest seed that has been germinated into a viable
plant was an approximately 1,300-yr-old lotus
fruit, recovered from a dry lakebed in northeastern China
Tree species that have well-developed dormancy needs may be tricked to some degree, but not completely. For instance, if a Japanese Maple
) is given an "eternal summer" through exposure to additional daylight, it will grow continuously for as long as two years. Eventually, however, a temperate climate plant will automatically go dormant, no matter what environmental conditions it experiences. Deciduous
plants will lose their leaves; evergreens
will curtail all new growth. Going through an "eternal summer" and the resultant automatic dormancy is stressful to the plant and usually fatal. The fatality rate increases to 100% if the plant does not receive the necessary period of cold temperatures required to break the dormancy. Most plants will require a certain number of hours of "chilling" at temperatures between about 0 °C and 10 °C to be able to break dormancy (Bewley JD, Black M. (1994). )
Bewley JD, Black M. (1994). Seeds: physiology of development
and germination, 2nd edn. New York, London: Plenum Press.
Black M, Butler J, Hughes M. (1987). Control and development
of dormancy in cereals. In: Mares DJ, ed. Fourth International
Symposium on Pre-Harvest Sprouting in Cereals, Boulder, Co.
USA: Westview Press, 379-92.
Scholar team (2002) SQA Adv. Higher Biology; Environmental Biology. p 93-95 Heriot Watt University