Dormancy

Dormancy is a period in an organism's life cycle when development 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.

Animal dormancy

Hibernation

Hibernation is a mechanism used by 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.

Diapause

Diapause 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 spring, 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.

Estivation

Estivation or aestivation (from Latin aestas, summer) is a rare state of dormancy similar to hibernation, but during the months of the summer. Animals that estivate spend a summer inactive and insulated against heat to avoid the potentially harmful effects of the season (such as the increase in temperature, or relative lack of water), or to avoid contact with other species with which they may otherwise be in competition, or for which they are prey. Some animals, including the California red-legged frog, may estivate to conserve energy when their food and water supply is low.

Both land-dwelling and aquatic mammals undergo estivation. Animals that estivate include North American desert tortoises, salamanders and lungfishes. The lungfish estivates by burying itself in mud formed at the surface of a dried up lake. In this state, the lungfish can survive for many years. Other animals estivate in their burrow and wait for autumn to come.

Snails also estivate during periods of heat during the day. They move into the vegetation, away from the ground heat, and secrete a membrane over the opening to their shell in order to prevent water loss.

Until recently no primate, and no tropical mammal, was known to estivate. However, animal physiologist Kathrin Dausmann of Philipps University of Marburg, Germany, and coworkers presented evidence in the 24 June 2004 edition of Nature that the Madagascan fat-tailed dwarf lemur hibernates or estivates in a small cricket hollow for seven months of the year.

Brumation

(information needed)

Torpor

Torpor 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.

Torpor is a state of regulated hypothermia in an endotherm lasting for periods ranging from just a few hours to several months. Animals that go through torpor include small birds like hummingbirds and some small mammals such as bats. During the active part of their day, these animals maintain normal body temperature and activity levels, but their body temperature drops during a portion of the day (usually night) to conserve energy. Torpor is often used to help animals survive in a cold climate, since it allows the organism to save the amount of energy that would normally be used to maintain a high body temperature. Some animals such as groundhogs, chipmunks, and jumping mice enter this state of hibernation for the duration of the winter. Lungfish switch to the torpor state if their pool dries out. Tenrecidae (common name tenrecs) switch to the torpor state if food is scarce during the summer (in Madagascar). Black bears, although often thought of as hibernators, do not truly enter a state of torpor. While their body temperatures lower along with respiration and heartbeat, they do not decrease as significantly as most animals in a state of torpor. Still, there is much debate about this within the scientific community, some feel that black bears are true hibernators that employ a more advanced form of hibernation.

Torpor is alternately used as a reference to any non-physiological state of inactivity. As an example, recently naturalists have learned that the female crocodile enters a deep torpor without aggression during their short egg laying period. This definition is also commonly used to describe the "chill out" effects of a number of psychotropic drugs, such as psychedelic mushrooms and LSD.

Torpor is also a term used in White Wolf's World of Darkness Vampire system to describe the result of a vampire being staked through the heart. The effects of this torpor are similar to paralysis.

Bacterial dormancy

Certain bacteria produce metabolically inactive forms that can survive intensely adverse conditions unharmed; these are known as cysts or endospores. This is a consequential strategy. Inactivating these resistant forms is usually done using an autoclave (pressurized heating device).

Plant dormancy

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.

Dormant seeds

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. 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. [1]

Tree dormancy

Tree species that have well-developed dormancy needs may be tricked to some degree, but not completely. For instance, if a Japanese Maple (Acer palmatum) 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.^{[citation needed]}

References

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Scholar team (2002) SQA Adv. Higher Biology; Environmental Biology. p 93-95 Heriot Watt University

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