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Acclimatization

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Not to be confused with Acclamation.

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), allowing it to maintain performance 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, which is a development that takes place over many generations). This may be a discrete occurrence (for example, when mountaineers acclimate to high altitude over hours or days) or may instead represent part of a periodic cycle, such as a mammal shedding heavy winter fur 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.[1] 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 and acclimation (and the corresponding verbs acclimatize and acclimate) are widely regarded as synonymous,[2][3][4][5][6][7] both in general vocabulary[2][3][4][5] and in medical vocabulary.[6][7] It has sometimes been asserted that they should be differentiated by reserving acclimatization for a wild/natural process (e.g., shedding heavy winter fur with natural seasonal change) and reserving acclimation for changes occurring in response to an artificial or controlled situation, such as changes in temperature imposed in an experiment. This assertion is not widely known or followed (as the foregoing citations of 6 major dictionaries show), so writers who intend it must explicitly state that it applies within their usage (for example, "in the following discussion, X refers strictly to Y") if they expect their intended meaning to be received by their audience. The synonym acclimatation[4][6] is less commonly encountered, and fewer dictionaries enter it.

Methods

Altitude

Climbers of Mount Everest must acclimatize to changes in O2, temperature, and humidity at many intervals during their climb and descent.

Acclimatization in response to high altitudes is a "truer" form of acclimatization in the sense that it fits both the general and physiological definitions. Increased altitude imposes a number of stressors — low temperature, less humidity, shifts in pH, and decreased oxygen concentration — that an organism must deal with in order to maintain function. This change in response to a complex environmental shift (involving many factors) is the epitome of physiological acclimatization. The process generally involves a change in metabolic pathways and respiratory function.[8]

Acclimatization to high altitude 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. This enhances the oxygen carrying capacity of the blood and helps to compensate for lower levels of oxygen intake.[9][10]

Temperature

Acclimatization in response to temperature is critical for a number of reasons; the most important of these is the maintenance of enzymatic reactions. A variety of physiological processes can be altered in order to maintain suitable temperature. When heat is elevated, humans produce a larger volume of sweat at more dilute concentrations to facilitate evaporative cooling (an unacclimatized person produces sweat with a salinity of up to 60 mEq/L, while an acclimatized person would produce sweat at around 5 mEq/L).[11][12] In addition, plasma volume, heart rate, and capillary activation are also affected.[13] Most organisms can adjust the chemical composition of their cell membranes to allow for more fluidity when it is cold and greater viscosity when it is hot, or code for heat shock proteins that may act as molecular chaperones and help the cell maintain function under periods of extreme stress.[14]

Organisms who allow their temperature to fluctuate, like many temperate lizards, have shown some ability to use behavioural processes for acclimatization.[15][16] These lizards showed superior functioning in their environments than lizards that lacked this capacity to acclimatize; these lizards were able to run and maintain activity levels that exceeded those of their non-acclimatized counterparts.[17]

Humidity

Humidity is one of the fundamental abiotic factors that determine which animals and plants can survive in a given environment.[18] While stomata and vein density is largely fixed based on adaptive evolution and natural selection, acclimatization to variable humidities can be achieved through differential epidermal cell expansion in many plants.[19]

Photoperiod

Photoperiodism is a form of acclimatization relative to the length of nights or dark periods. It is primarily observed in plants but can also be observed in animals. Many angiosperms use photoreceptor proteins — like cytochromes or phytochromes — to detect changes in photoperiod and acclimatize accordingly.[20] Plants can be classified into three groups relative to their photoperiodic changes and flowering tendencies: short-day plants (for example, rice)[21], long-day plants (like carnations)[22], and day-neutral plants (like roses)[23].

pH

pH is the measure of the acidity or basicity of an aqueous solution.[24] pH levels can have immense effects on an organism; from organ-level operation all the way down to cellular and enzymatic functioning. A notable example of pH acclimatization is the process by which tropical fish are attuned to domestic fish tanks through the use of acclimatization bags. In incremental steps, the fish are exposed to bags with more neutral pH until they are ready to be transferred to the tank.[25]

Salinity

The regulation of salinity (the concentration of salt dissolved in water) and the correlated process of osmoregulation are critical to ensuring proper organism function.[26] The cells of organisms are bathed in aqueous mediums. If the medium has an excess proportion of salt (or other solutes) than cells may crenate; if the medium has too little salt (or other solutes) than cells may lyse.[27] Migratory fish species may be anadromous (migrating from sea to freshwater) or catadromous(migrating from freshwater to sea). Regardless of their classification, migratory fish — like salmon and bass[28] — are able to adjust to changes in salinity through gradual acclimatization as they move down gradients between habitats. However, if these fish were to be translocated directly between habitats with different salinity without gradual acclimatization, many would be unable to survive.[29][30]

Research

Beneficial acclimation hypothesis

Since researchers first began to study acclimatization, the overwhelming hypothesis has been that all acclimatization functions to enhance the performance of an organism. This idea has come to be known as the beneficial acclimation hypothesis. Despite early widespread support, studies have arose that show that acclimatization does not always serve to enhance performance. One of the major objections to the beneficial acclimation hypothesis is that it assumes that there are no costs associated with acclimatization.[31] However, a number of costs have been identified. These include the costs of sensing environmental conditions and regulating responses, producing the structures required for plasticity (e.g., the energetic costs that come with expressing heat shock proteins), and a variety of genetic tradeoffs (e.g., linkage of plasticity-related genes with harmful genes).[32]

Contemporary study

Given the shortcomings of the beneficial acclimation hypothesis, researchers are continuing to search for a theory that can be supported by empirical data. Contemporary research on acclimatization has focused more heavily on the evolution of phenotypic plasticity rather than acclimatization responses. Scientists believe that if they can comprehend how organisms evolved the capacity to acclimatize, they can better understand the mechanisms by which the process itself is carried out.[33][34] Furthermore, current research is often oriented towards how anthropogenic influences may act on developed acclimatization responses.[35]

See also

References

  1. ^ (2009) “Acclimatisation” (n.d.) The Unabridged Hutchinson Encyclopedia Retrieved November 5 2009 from http://encyclopedia.farlex.com/acclimatization
  2. ^ a b Oxford Dictionaries, Oxford Dictionaries Online, Oxford University Press.
  3. ^ a b Merriam-Webster, Merriam-Webster's Collegiate Dictionary, Merriam-Webster.
  4. ^ a b c Merriam-Webster, Merriam-Webster's Unabridged Dictionary, Merriam-Webster.
  5. ^ a b Houghton Mifflin Harcourt, The American Heritage Dictionary of the English Language, Houghton Mifflin Harcourt, archived from the original on 2015-09-25, retrieved 2017-01-31.
  6. ^ a b c Elsevier, Dorland's Illustrated Medical Dictionary, Elsevier.
  7. ^ a b Wolters Kluwer, Stedman's Medical Dictionary, Wolters Kluwer.
  8. ^ Nilsson, Göran (2010). Respiratory Physiology of Vertebrates : Life With and Without Oxygen. Cambridge: Cambridge University Press. pp. 265–282. ISBN 9780521878548.
  9. ^ Muza, SR; Fulco, CS; Cymerman, A (2004). "Altitude Acclimatization Guide". US Army Research Inst. Of Environmental Medicine Thermal and Mountain Medicine Division Technical Report (USARIEM–TN–04–05). Archived from the original on 2009-04-23. Retrieved 2009-03-05.
  10. ^ Kenneth Baillie; Alistair Simpson. "Altitude oxygen calculator". Apex (Altitude Physiology EXpeditions). Archived from the original on 2017-06-11. Retrieved 2006-08-10. - Altitude physiology model
  11. ^ "Heat acclimatization guide" (PDF). US Army. Archived from the original (PDF) on 2007-07-02. Retrieved 2009-07-02.
  12. ^ Piantadosi, Claude (2003). The Biology of Human Survival : Life and Death in Extreme Environments. Oxford: Oxford University Press. ISBN 9780195165012.
  13. ^ "Heat Acclimatization". www.sportsci.org. Retrieved 2017-12-03.
  14. ^ Los D.A., Murata N. (2004). "Membrane fluidity and its roles in the perception of environmental signals". Biochimica et Biophysica Acta (BBA) - Biomembranes. 0666 (1–2): 142–157. doi:10.1016/j.bbamem.2004.08.002. PMID 15519313.
  15. ^ Hazel, J R; Prosser, C L (1974). "Molecular mechanisms of temperature compensation in poikilotherms". Physiological Reviews. 54 (3): 620–677. doi:10.1152/physrev.1974.54.3.620. ISSN 0031-9333.
  16. ^ Taylor, Emily N. (2017). "Review of Amphibian and Reptile Adaptations to the Environment: Interplay Between Physiology and Behavior". Copeia. 105 (1): 171–173. doi:10.2307/26872415. ISSN 0045-8511.
  17. ^ Lowe C.H., Vance V.J. (1955). "Acclimation of the critical thermal maximum of the reptile Urosaurus ornatus". Science. 122 (3158): 73–74. Bibcode:1955Sci...122...73L. doi:10.1126/science.122.3158.73. PMID 17748800.
  18. ^ C.Michael Hogan. 2010. Abiotic factor. Encyclopedia of Earth. eds Emily Monosson and C. Cleveland. National Council for Science and the Environment Archived June 8, 2013, at the Wayback Machine. Washington DC
  19. ^ Carins Murphy, Madeline R.; Jordan, Gregory J.; Brodribb, Timothy J. (2014). "Acclimation to humidity modifies the link between leaf size and the density of veins and stomata: VPD alters the link between leaf size and anatomy". Plant, Cell & Environment. 37 (1): 124–131. doi:10.1111/pce.12136.
  20. ^ Mauseth, James D. (2003). Botany : An Introduction to Plant Biology (3rd ed.). Sudbury, MA: Jones and Bartlett Learning. pp. 422–27. ISBN 978-0-7637-2134-3.
  21. ^ BSCS Biology (9 ed.). BSCS. 2002. p. 519. ISBN 978-0-7872-9008-5.
  22. ^ Starr, Cecie; Taggart, Ralph; Evers, Christine; Starr, Lisa (2013). Plant Structure and Function. Vol. 4 (13th ed.). Brooks/Cole. p. 517. ISBN 978-1-111-58068-1.
  23. ^ Meneely, Philip (2014). Genetic Analysis: Genes, Genomes, and Networks in Eukaryotes (2 ed.). Oxford University Press. p. 373. ISBN 978-0-19-968126-6.
  24. ^ Jensen, William B. (2004). "The Symbol for pH" (PDF). Journal of Chemical Education. 81 (1): 21. Bibcode:2004JChEd..81...21J. doi:10.1021/ed081p21.
  25. ^ "Acclimating Your Fish".
  26. ^ Pawlowicz, R. (2013). "Key Physical Variables in the Ocean: Temperature, Salinity, and Density". Nature Education Knowledge. 4 (4): 13.
  27. ^ Alberts, Bruce (2014). Essential cell biology (Fourth ed.). New York: Garland Science. ISBN 978-0-8153-4454-4. OCLC 852218989.
  28. ^ Moyle, P.B. 2004. Fishes: An Introduction to Ichthyology. Pearson Benjamin Cummings, San Francisco, CA.
  29. ^ Ortiz, Rudy M. (2001-06-01). "Osmoregulation in Marine Mammals". Journal of Experimental Biology. 204 (11): 1831–1844. ISSN 0022-0949. PMID 11441026.
  30. ^ Dingle, Hugh and Drake, V. Alistair (2007) "What Is Migration?". BioScience, 57(2):113–121. doi:10.1641/B570206
  31. ^ Angilletta, M.J. (2009). Thermal Adaptation: A Theoretical and Empirical Synthesis. Oxford University Press, Oxford.
  32. ^ DeWitt, Thomas J.; Sih, Andrew; Wilson, David Sloan (1998-02-01). "Costs and limits of phenotypic plasticity". Trends in Ecology & Evolution. 13 (2): 77–81. doi:10.1016/S0169-5347(97)01274-3. PMID 21238209.
  33. ^ Tufts, D. M.; Revsbech, I. G.; Cheviron, Z. A.; Weber, R. E.; Fago, A.; Storz, J. F. (2013-04-01). "Phenotypic plasticity in blood-oxygen transport in highland and lowland deer mice". Journal of Experimental Biology. 216 (7): 1167–1173. doi:10.1242/jeb.079848. ISSN 0022-0949. PMC 3603338. PMID 23239893.
  34. ^ Hochachka, Peter W. (2002). Biochemical adaptation : mechanism and process in physiological evolution. George N. Somero. New York: Oxford University Press. ISBN 978-0-19-535367-9. OCLC 57469409.
  35. ^ Sawall, Yvonne; Al-Sofyani, Abdulmoshin; Hohn, Sönke; Banguera-Hinestroza, Eulalia; Voolstra, Christian R.; Wahl, Martin (2015). "Extensive phenotypic plasticity of a Red Sea coral over a strong latitudinal temperature gradient suggests limited acclimatization potential to warming". Scientific Reports. 5 (1): 8940. doi:10.1038/srep08940. ISSN 2045-2322. PMC 5155415. PMID 25754672.
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