Dormancy

Dormancy is a general term used to describe a period in an organism's life cycle when metabolic activity is minimized and active development is temporarily suspended. Thus, it 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. This energy saving mode of the animal is characterized by many physiological changes, mainly the decreased body temperature, decreased heart rate (by as much as 95%) and lower metabolic rate. Time migration, as it is often called may last several days or weeks depending on species, ambient temperature, and time of the year. 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. Hibernation may be predictive or consequential. 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

Each bacterial group is ubiquitous occurring nearly everywhere and is easily dispersible. Therefore, the bacteria may not need dormant forms to overcome the adverse environmental condition. However, there are certain bacteria which produce metabolically inactive forms that can survive adverse conditions unharmed. The species of Gram-positive genera Bacillus, Clostridium, Desulfotomaculum, Sporolactobacillus and Sarcina form endospores on confronting the adverse environmental conditions like lack of water or depletion of essential nutrients, etc. This is a consequential dormancy. The endospores are formed in the spore mother cells, one per one mother cell. Each endospore contain endospore specific dipicolic acid (pyridin-2,6-dicarbonic acid) upto 15% of the dry weight. The endospore is surrounded by exosporium, outer covering, inner covering, cortex, cell wall and cell membrane; thus, the protective coverings alone form about 50% of the volume and dry weight of the whole endospore. Therefore, endospores are thermoresistant, drought resistant, resistant to many chemical and radiation treatments. It has been reported that even from 50 years old dried soil, 90% of the endospores could germinate into viable cells. Pasteurization is not enough to kill the endospores, these resistant forms are inactivated usually by sterilization in an autoclave by heating at 121 degree Celsius under 15 lb per centimeter squar steam pressure for 15 minutes. Besides endospores, some bacteria develop exospores (e.g., Methylosinus trichosporium) or undergo encystment to form cysts (e.g., the species of genera Methylocystis and Azotobacter). Many species of Azotobacter can withstand drying of the soil for significantly long time without undergoing any structural or physiological change.

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. Innate dormancy occurs whether or not external conditions are suitable. Most plants of temperate regions pass through a phase of innate dormancy coinciding with an unfavourable season. But several species of annual weeds like groundsel (Senecio vulgaris), shepherd's purse (Capsella bursa-pastoris), chickenweed (Cerastim spp.) show imposed dormancy only in the very cold weather.

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. This clock works through decreased temperatures, shortened day length, or a reduction in rainfall. In higher plants, innate dormancy involves seeds, underground organs such as rhizomes, corms or tuber and the winter buds of woody twigs.

Seed dormancy

If a seed fails to germinate even when it is placed under favorable conditions, then the seed is said to be dormant. Many seeds especially those of wild plants do not germinate as soon as they are formed and dispersed. If seeds germinated as soon as they were shed in late summer or early autumn, they would produce plants that might succumb to harsh winter conditions before they could reproduce. Thus, dormancy helps to avoid this hazard. The oldest seed that has been germinated into a viable plant was an approximately 1,300-yr-old lotus fruit, recovered from a dry lake bed in northeastern China. [1] 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 (e.g., Acer sps.). Seed coat of some desert plants contains chemicals which inhibit its own seed germination until they are completely wash away by sufficient rain; this dormancy is to avoid scarcity of water. The second type of seed dormancy is called embryo dormancy or internal dormancy, and is caused by a condition of the embryo like incomplete development or structural or physiological immaturity. Under normal conditions, the seed matures in time, and the thick seed coat is weakened by abrasion in the soil and by the action of soil microorganisms. However, the dormancy of seeds of many species can be overcomed by low temperatures. For this to be effective, the seeds require temperatures of 0 to 5 degree Celsius for two or three weeks.

Bud dormancy

In the temperate zones, the growing parts of the stems of the trees and shrubs are well protected from winter cold by special buds called winter buds. In these winter buds, the growing meristem and the immature foliage leaves are covered by many layers of scale leaves externally. They are formed in summer while growing conditions are still favorable. Although formed in the growing season, these buds do not normally break until after passing through the cold winter. However, if the trees suffer from unexpected defoliation, then the buds will grow and produce second wave of foliage in the same season. It seems that late autumn innate dormancy of buds is established and triggered by short photoperiod of autumn. 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

ISBN links support NWE through referral fees

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

C.J.Clegg and D.G. Mackean (2000) Adv. Biology: Principles and Applications. P 438-439 John Murray (Publishers) Ltd.

Hans G. Schlegel and Christiane Zaborosch (1992) Allgemeine Mikrobiologie. p 79-84 Georg Thieme Verlag Stuttgart

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