Acclimatization
or acclimatisation (
also called acclimation or acclimatation) is the process in which an individual
organism
In biology, an organism () is any living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are classified by taxonomy into groups such as multicellular animals, plants, and ...
adjusts to a
change in its environment (such as a change in altitude, temperature, humidity,
photoperiod
Photoperiodism is the physiological reaction of organisms to the length of night or a dark period. It occurs in plants and animals. Plant photoperiodism can also be defined as the developmental responses of plants to the relative lengths of light a ...
, or
pH), allowing it to maintain
fitness across a range of environmental conditions. Acclimatization occurs in a short period of time (hours to weeks), and within the organism's lifetime (compared to
adaptation
In biology, adaptation has three related meanings. Firstly, it is the dynamic evolutionary process of natural selection that fits organisms to their environment, enhancing their evolutionary fitness. Secondly, it is a state reached by the po ...
, which is evolution, taking place over many generations). This may be a discrete occurrence (for example, when
mountaineers
Mountaineering or alpinism, is a set of outdoor activities that involves ascending tall mountains. Mountaineering-related activities include traditional outdoor climbing, skiing, and traversing via ferratas. Indoor climbing, sport climbing, an ...
acclimate to
high altitude
Altitude or height (also sometimes known as depth) is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The exact definition and reference datum varies according to the context ...
over hours or days) or may instead represent part of a periodic cycle, such as a
mammal
Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...
shedding heavy winter
fur
Fur is a thick growth of hair that covers the skin of mammals. It consists of a combination of oily guard hair on top and thick underfur beneath. The guard hair keeps moisture from reaching the skin; the underfur acts as an insulating blanket t ...
in favor of a lighter summer coat. Organisms can adjust their morphological, behavioral, physical, and/or biochemical traits in response to changes in their environment. While the capacity to acclimate to novel environments has been well documented in thousands of species, researchers still know very little about how and why organisms acclimate the way that they do.
Names
The nouns ''
acclimatization
Acclimatization or acclimatisation ( also called acclimation or acclimatation) is the process in which an individual organism adjusts to a change in its environment (such as a change in altitude, temperature, humidity, photoperiod, or pH), ...
'' and ''
acclimation
Acclimatization or acclimatisation ( also called acclimation or acclimatation) is the process in which an individual organism adjusts to a change in its environment (such as a change in altitude, temperature, humidity, photoperiod, or pH), a ...
'' (and the corresponding verbs ''
acclimatize
Acclimatization or acclimatisation ( also called acclimation or acclimatation) is the process in which an individual organism adjusts to a change in its environment (such as a change in altitude, temperature, humidity, photoperiod, or pH), a ...
'' and ''
acclimate
Acclimatization or acclimatisation ( also called acclimation or acclimatation) is the process in which an individual organism adjusts to a change in its environment (such as a change in altitude, temperature, humidity, photoperiod, or pH), a ...
'') are widely regarded as
synonym
A synonym is a word, morpheme, or phrase that means exactly or nearly the same as another word, morpheme, or phrase in a given language. For example, in the English language, the words ''begin'', ''start'', ''commence'', and ''initiate'' are all ...
ous,
both in general vocabulary
and in medical vocabulary.
The synonym ''
acclimatation
Acclimatization or acclimatisation ( also called acclimation or acclimatation) is the process in which an individual organism adjusts to a change in its environment (such as a change in altitude, temperature, humidity, photoperiod, or pH), ...
''
is less commonly encountered, and fewer dictionaries enter it.
Methods
Biochemical
In order to maintain performance across a range of environmental conditions, there are several strategies organisms use to acclimate. In response to changes in temperature, organisms can change the biochemistry of
cell membrane
The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of all cells from the outside environment ( ...
s making them more fluid in cold temperatures and less fluid in warm temperatures by increasing the number of
membrane protein
Membrane proteins are common proteins that are part of, or interact with, biological membranes. Membrane proteins fall into several broad categories depending on their location. Integral membrane proteins are a permanent part of a cell membrane ...
s.
In response to certain stressors, some organisms express so-called
heat shock protein
Heat shock proteins (HSP) are a family of proteins produced by cells in response to exposure to stressful conditions. They were first described in relation to heat shock, but are now known to also be expressed during other stresses including expo ...
s that act as
molecular chaperones
In molecular biology, molecular chaperones are proteins that assist the conformational folding or unfolding of large proteins or macromolecular protein complexes. There are a number of classes of molecular chaperones, all of which function to ass ...
and reduce
denaturation by guiding the
folding
Fold, folding or foldable may refer to:
Arts, entertainment, and media
* ''Fold'' (album), the debut release by Australian rock band Epicure
* Fold (poker), in the game of poker, to discard one's hand and forfeit interest in the current pot
*Abov ...
and refolding of proteins. It has been shown that organisms which are acclimated to high or low temperatures display relatively high resting levels of heat shock proteins so that when they are exposed to even more extreme temperatures the proteins are readily available. Expression of heat shock proteins and regulation of membrane fluidity are just two of many biochemical methods organisms use to acclimate to novel environments.
Morphological
Organisms are able to change several characteristics relating to their
morphology
Morphology, from the Greek and meaning "study of shape", may refer to:
Disciplines
* Morphology (archaeology), study of the shapes or forms of artifacts
* Morphology (astronomy), study of the shape of astronomical objects such as nebulae, galaxies ...
in order to maintain performance in novel environments. For example, birds often increase their organ size to increase their metabolism. This can take the form of an increase in the mass of nutritional organs or heat-producing organs, like the pectorals (with the latter being more consistent across species
).
The theory
While the capacity for acclimatization has been documented in thousands of species, researchers still know very little about how and why organisms acclimate in the way that they do. Since researchers first began to study acclimation, the overwhelming hypothesis has been that all acclimation serves to enhance the performance of the organism. This idea has come to be known as the
beneficial acclimation hypothesis
The beneficial acclimation hypothesis (BAH) is the physiology, physiological hypothesis that acclimatization, acclimating to a particular environment (usually thermal) provides an organism with advantages in that environment. First formally teste ...
. Despite such widespread support for the beneficial acclimation hypothesis, not all studies show that acclimation always serves to enhance performance (''See
beneficial acclimation hypothesis
The beneficial acclimation hypothesis (BAH) is the physiology, physiological hypothesis that acclimatization, acclimating to a particular environment (usually thermal) provides an organism with advantages in that environment. First formally teste ...
''). One of the major objections to the beneficial acclimation hypothesis is that it assumes that there are no costs associated with acclimation.
[Angilletta, M.J. (2009). Thermal Adaptation: A Theoretical and Empirical Synthesis. Oxford University Press, Oxford.] However, there are likely to be costs associated with acclimation. These include the cost of sensing the environmental conditions and regulating responses, producing structures required for plasticity (such as the energetic costs in expressing
heat shock protein
Heat shock proteins (HSP) are a family of proteins produced by cells in response to exposure to stressful conditions. They were first described in relation to heat shock, but are now known to also be expressed during other stresses including expo ...
s), and genetic costs (such as linkage of plasticity-related genes with harmful genes).
Given the shortcomings of the beneficial acclimation hypothesis, researchers are continuing to search for a theory that will be supported by empirical data.
The degree to which organisms are able to acclimate is dictated by their
phenotypic plasticity
Phenotypic plasticity refers to some of the changes in an organism's behavior, morphology and physiology in response to a unique environment. Fundamental to the way in which organisms cope with environmental variation, phenotypic plasticity encompa ...
or the ability of an organism to change certain traits. Recent research in the study of acclimation capacity has focused more heavily on the evolution of phenotypic plasticity rather than acclimation responses. Scientists believe that when they understand more about how organisms evolved the capacity to acclimate, they will better understand acclimation.
Examples
Plants
Many plants, such as
maple tree
''Acer'' () is a genus of trees and shrubs commonly known as maples. The genus is placed in the family Sapindaceae.Stevens, P. F. (2001 onwards). Angiosperm Phylogeny Website. Version 9, June 2008 nd more or less continuously updated since http ...
s,
irises, and
tomato
The tomato is the edible berry of the plant ''Solanum lycopersicum'', commonly known as the tomato plant. The species originated in western South America, Mexico, and Central America. The Mexican Nahuatl word gave rise to the Spanish word ...
es, can survive freezing temperatures if the temperature gradually drops lower and lower each night over a period of days or weeks. The same drop might kill them if it occurred suddenly. Studies have shown that tomato plants that were acclimated to higher temperature over several days were more efficient at photosynthesis at relatively high temperatures than were plants that were not allowed to acclimate.
In the orchid ''
Phalaenopsis
''Phalaenopsis'' (), also known as moth orchids, is a genus of about seventy species of plants in the family Orchidaceae. Orchids in this genus are monopodial epiphytes or lithophytes with long, coarse roots, short, leafy stems and long-lasting ...
'',
phenylpropanoid enzymes are enhanced in the process of plant acclimatisation at different levels of
photosynthetic
Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored in c ...
photon flux.
Animals
Animals acclimatize in many ways.
Sheep
Sheep or domestic sheep (''Ovis aries'') are domesticated, ruminant mammals typically kept as livestock. Although the term ''sheep'' can apply to other species in the genus ''Ovis'', in everyday usage it almost always refers to domesticated s ...
grow very thick
wool
Wool is the textile fibre obtained from sheep and other mammals, especially goats, rabbits, and camelids. The term may also refer to inorganic materials, such as mineral wool and glass wool, that have properties similar to animal wool.
As ...
in cold, damp climates.
Fish
Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of li ...
are able to adjust only gradually to changes in water temperature and quality. Tropical fish sold at
pet store
A pet shop or pet store is a retail business which sells animals and pet care resources to the public. A variety of animal supplies and pet accessories are also sold in pet shops. The products sold include: food, treats, toys, collars, leashes, ca ...
s are often kept in
acclimatization bags
Acclimatization or acclimatisation ( also called acclimation or acclimatation) is the process in which an individual organism adjusts to a change in its environment (such as a change in altitude, temperature, humidity, photoperiod, or pH), a ...
until this process is complete. Lowe & Vance (1995) were able to show that lizards acclimated to warm temperatures could maintain a higher running speed at warmer temperatures than lizards that were not acclimated to warm conditions.
Fruit flies that develop at relatively cooler or warmer temperatures have increased cold or heat tolerance as adults, respectively (''See''
Developmental plasticity
Developmental plasticity is a general term referring to changes in neural connections during development as a result of environmental interactions as well as neural changes induced by learning. Much like neuroplasticity or brain plasticity, develo ...
).
Humans
The
salt
Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quantitie ...
content of sweat and urine decreases as people acclimatize to hot conditions.
Plasma volume, heart rate, and capillary activation are also affected.
Acclimatization to high altitude
The effects of high altitude on humans are mostly the consequences of reduced partial pressure of oxygen in the atmosphere. The oxygen saturation of hemoglobin determines the content of oxygen in blood. After the human body reaches around above ...
continues for months or even years after initial ascent, and ultimately enables humans to survive in an environment that, without acclimatization, would kill them. Humans who migrate permanently to a higher altitude naturally acclimatize to their new environment by developing an increase in the number of
red blood cells
Red blood cells (RBCs), also referred to as red cells, red blood corpuscles (in humans or other animals not having nucleus in red blood cells), haematids, erythroid cells or erythrocytes (from Greek language, Greek ''erythros'' for "red" and ''k ...
to increase the
oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...
carrying capacity of the
blood
Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells, and transports metabolic waste products away from those same cells. Blood in the c ...
, in order to compensate for lower levels of
oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...
intake.
[ - Altitude physiology model]
See also
*
Acclimatisation society Acclimatisation societies were voluntary associations in the 19th and 20th centuries that encouraged the introduced species, introduction of non-native species in various places around the world, in the hope that they would acclimatization, acclimat ...
*
Beneficial acclimation hypothesis
The beneficial acclimation hypothesis (BAH) is the physiology, physiological hypothesis that acclimatization, acclimating to a particular environment (usually thermal) provides an organism with advantages in that environment. First formally teste ...
*
Heat index
The heat index (HI) is an index that combines air temperature and relative humidity, in shaded areas, to posit a human-perceived equivalent temperature, as how hot it would feel if the humidity were some other value in the shade. The result is als ...
*
Introduced species
An introduced species, alien species, exotic species, adventive species, immigrant species, foreign species, non-indigenous species, or non-native species is a species living outside its native distributional range, but which has arrived there ...
*
Phenotypic plasticity
Phenotypic plasticity refers to some of the changes in an organism's behavior, morphology and physiology in response to a unique environment. Fundamental to the way in which organisms cope with environmental variation, phenotypic plasticity encompa ...
*
Wind chill
Wind chill or windchill (popularly wind chill factor) is the lowering of body temperature due to the passing-flow of lower-temperature air.
Wind chill numbers are always lower than the air temperature for values where the formula is valid. When ...
References
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Physiology
Ecological processes
Climate