CHAPTER OVERVIEW 4: Adaptations to the Physical Environment Learning Objectives Describe what an adaptation is and how it arises, and explain examples of common adaptations in plants and animals. Compare and contrast some of the broad strategies organisms employ to deal with a variable environment. Explain how individual physiological performance can vary with the environment, and link these concepts with population distribution limits and climate change. 4.1: What is adaptation? 4.2: Strategies for dealing with a changing environment 4.3: Adaptations to avoid harsh conditions 4.4: Physiological optima and critical limits Summary In biology, adaptation is defined a heritable behavioral, morphological, or physiological trait that has evolved through the process of natural selection, and maintains or increases the fitness of an organism under a given set of environmental conditions. This concept is central to ecology: the study of adaptation is the study of the evolutionary relationship between organisms and their environment. While different groups of plants and animals have adapted to components of their environment in many different ways, more broadly, the two basic solutions for dealing with environmental variation are to conform to the environment or to regulate internal conditions despite the environment. These different strategies influence an organism's physiological performance across variable environmental conditions. Contributors and Attributions 4: Adaptations to the Physical Environment is shared under a CC BY-NC-SA license and was authored, remixed, and/or curated by LibreTexts.
4.1: What is adaptation? Adaptation In biology, adaptation is defined a heritable behavioral, morphological, or physiological trait that has evolved through the process of natural selection, and maintains or increases the fitness of an organism under a given set of environmental conditions. This concept is central to ecology: the study of adaptation is the study of the evolutionary relationship between organisms and their environment. Adaptation is related to biological fitness, which governs the rate of evolution as measured by change in gene frequencies. Often, two or more species co-adapt and co-evolve as they develop adaptations that interlock with those of the other species, such as with flowering plants and pollinating insects. Features evolved for one purpose may be co-opted for a different one, as when the insulating feathers of dinosaurs were co-opted for bird flight. History Adaptation is an observable fact of life accepted by philosophers and natural historians from ancient times, independently of their views on evolution, but their explanations differed. In natural theology, adaptation was interpreted as the work of a deity and as evidence for the existence of God (Desmond, 1989). Charles Darwin broke with the tradition by emphasizing the flaws and limitations which occurred in the animal and plant worlds (Darwin, 1872). Jean-Baptiste Lamarck proposed a tendency for organisms to become more complex, moving up a ladder of progress, plus "the influence of circumstances," usually expressed as use and disuse (Bowler, 1989). This second, subsidiary element of his theory is what is now called Lamarckism, a proto-evolutionary hypothesis of the inheritance of acquired characteristics, intended to explain adaptations by natural means (Bowler, 2003).
Figure : The second of Jean-Baptiste Lamarck's two factors (the first being a complexifying force) was an adaptive force that causes animals with a given body plan to adapt to circumstances by inheritance of acquired characteristics, creating a diversity of
species and genera. Other natural historians, such as Buffon, accepted adaptation, and some also accepted evolution, without voicing their opinions as to the mechanism. This illustrates the real merit of Darwin and Alfred Russel Wallace, and secondary figures such as Henry Walter Bates, for putting forward a mechanism whose significance had only been glimpsed previously. A century later, experimental field studies and breeding experiments by people such as E.B. Ford and Theodosius Dobzhansky produced evidence that natural selection was not only the 'engine' behind adaptation, but was a much stronger force than had previously been thought (Provine, 1986; Ford, 1975; Orr, 2005). General principles The significance of an adaptation can only be understood in relation to the total biology of the species. -- Julian Huxley, Evolution: The Modern Synthesis (Huxley, 1942) What adaptation is Adaptation is primarily a process rather than a physical form or part of a body (Mayr, 1982). An internal parasite (such as a liver fluke) can illustrate the distinction: such a parasite may have a very simple bodily structure, but nevertheless the organism is highly
adapted to its specific environment. From this we see that adaptation is not just a matter of visible traits: in such parasites critical adaptations take place in the life cycle, which is often quite complex (Price, 1980). However, as a practical term, "adaptation" often refers to a product: those features of a species which result from the process. Many aspects of an animal or plant can be correctly called adaptations, though there are always some features whose function remains in doubt. By using the term adaptation for the evolutionary process, and adaptive trait for the bodily part or function (the product), one may distinguish the two different senses of the word (Daintith & Martin, 2010; Bowler, 2003; Patterson, 1999; Williams, 1966). Adaptation is one of the two main processes that explain the observed diversity of species, such as the different species of Darwin's finches. The other process is speciation, in which new species arise, typically through reproductive isolation (Mayr, 1963; Mayr, 1982). An example widely used today to study the interplay of adaptation and speciation is the evolution of cichlid fish in African lakes, where the question of reproductive isolation is complex (Mack et al., 2005; Kornfield & Smith, 2000). Adaptation is not always a simple matter where the ideal phenotype evolves for a given environment. An organism must be viable at all stages of its development and at all stages of its evolution. This places constraints on the evolution of development, behavior, and structure of organisms. The main constraint, over which there has been much debate, is the requirement that each genetic and phenotypic change during evolution should be relatively small, because developmental systems are so complex and interlinked. However, it is not clear what "relatively small" should mean, for example polyploidy in plants is a reasonably common large genetic change (Stebbins, 1950). The origin of eukaryotic endosymbiosis is a more dramatic example (Margulis & Fester, 1991). All adaptations help organisms survive in their ecological niches. The adaptive traits may be structural, behavioral or physiological. Structural adaptations are physical features of an organism, such as shape, body covering, armament, and internal organization. Behavioral adaptations are inherited systems of behavior, whether inherited in detail as instincts, or as a neuropsychological capacity for learning. Examples include searching for food, mating, and vocalizations. Physiological adaptations permit the organism to perform special functions such as making venom, secreting slime, and phototropism, but also involve more general functions such as growth and development, temperature regulation, ionic balance and other aspects of homeostasis. Adaptation affects all aspects of the life of an organism (Hutchinson, 1965). The following definitions are given by the evolutionary biologist Theodosius Dobzhansky: 1. Adaptation is the evolutionary process whereby an organism becomes better able to live in its habitat or habitats (Dobzhansky, 1968; Wang, 2014; Sejian et al., 2015). 2. Adaptedness is the state of being adapted: the degree to which an organism is able to live and reproduce in a given set of habitats (Dobzhansky, 1970). 3. An adaptive trait is an aspect of the developmental pattern of the organism which enables or enhances the probability of that organism surviving and reproducing (Dobzhansky, 1956). What adaptation is not Adaptation differs from flexibility, acclimatization, and learning, all of which are changes during life which are not inherited. Flexibility deals with the relative capacity of an organism to maintain itself in different habitats: its degree of specialization. Acclimatization describes automatic physiological adjustments during life; learning means improvement in behavioral performance during life (Pillay et al., 2013; Gross, 2012). Flexibility stems from phenotypic plasticity, the ability of an organism with a given genotype (genetic type) to change its phenotype (observable characteristics) in response to changes in its habitat, or to move to a different habitat (Irwin et al., 2003; Price, 2006). The degree of flexibility is inherited, and varies between individuals. A highly specialized animal or plant lives only in a well-defined habitat, eats a specific type of food, and cannot survive if its needs are not met. Many herbivores are like this; extreme examples are koalas which depend on Eucalyptus, and giant pandas which require bamboo. A generalist, on the other hand, eats a range of food, and can survive in many different conditions. Examples are humans, rats, crabs and many carnivores. The tendency to behave in a specialized or exploratory manner is inherited--it is an adaptation. Rather different is developmental flexibility: "An animal or plant is developmentally flexible if when it is raised in or transferred to new conditions, it changes in structure so that it is better fitted to survive in the new environment," writes evolutionary biologist John Maynard Smith (Smith, 1993).
Figure : Some generalists, such as birds, have the flexibility to adapt to urban areas.
If humans move to a higher altitude, respiration and physical exertion become a problem, but after spending time in high altitude conditions they acclimatize to the reduced partial pressure of oxygen, such as by producing more red blood cells. The ability to acclimatize is an adaptation, but the acclimatization itself is not. The reproductive rate declines, but deaths from some tropical diseases also go down. Over a longer period of time, some people are better able to reproduce at high altitudes than others. They contribute more heavily to later generations, and gradually by natural selection the whole population becomes adapted to the new conditions. This has demonstrably occurred, as the observed performance of long-term communities at higher altitude is significantly better than the performance of new arrivals, even when the new arrivals have had time to acclimatize (Moore & Regensteiner, 1983). Adaptedness and fitness There is a relationship between adaptedness and the concept of fitness used in population genetics. Differences in fitness between genotypes predict the rate of evolution by natural selection. Natural selection changes the relative frequencies of alternative phenotypes, insofar as they are heritable (Endler, 1986). However, a phenotype with high adaptedness may not have high fitness. Dobzhansky mentioned the example of the Californian redwood, which is highly adapted, but a relict species in danger of extinction (Dobzhansky, 1968). Elliott Sober commented that adaptation was a retrospective concept since it implied something about the history of a trait, whereas fitness predicts a trait's future (Sober, 1984). 1. Relative fitness- the average contribution to the next generation by a genotype or a class of genotypes, relative to the contributions of other genotypes in the population (Futuyma, 1986). This is also known as Darwinian fitness, selection coefficient, and other terms. 2. Absolute fitness - the absolute contribution to the next generation by a genotype or a class of genotypes. Also known as the Malthusian parameter when applied to the population as a whole (Endler, 1986; Fisher, 1930). 3. Adaptedness - the extent to which a phenotype fits its local ecological niche. Researchers can sometimes test this through a reciprocal transplant, which involves taking organisms evolved in different locations and swapping where they are located to determine if fitness is reduced. Transplant experiments are often used to test if there is a genetic component to differences in populations (Gaggiotti et al., 2015).
: In this sketch of a fitness landscape, a population can evolve by following the arrows to the adaptive peak at point B, and the points A and C are local optima where a population could become trapped.
Sewall Wright proposed that populations occupy adaptive peaks on a fitness landscape. To evolve to another, higher peak, a population would first have to pass through a valley of maladaptive intermediate stages, and might be "trapped" on a peak that is not optimally adapted (Wright, 1932).
Definition: Reciprocal transplant experiment Testing for local adaptation requires measuring the fitness of organisms from one population in both their local environment and in foreign environments. This is often done using transplant experiments. Using the stricter definition of reciprocal home
site advantage, local adaptation is often tested via reciprocal transplant experiments. In reciprocal transplants, organisms from one population are transplanted into another population, and vice versa, and their fitness is measured (see figure) (Ebert & Kawecki, 2004). If local transplants outperform (i.e. have higher fitness than) the foreign transplants at both sites, the local populations are said to be locally adapted (Fenster & Galloway, 2000). If local adaptation is defined simply as a home site advantage of one population (local sources outperform foreign sources at a common site), it can be tested for using common garden experiments, where multiple source populations are grown in a common site, as long as one of the source populations is local to that site. Transplant experiments have most often been done with plants or other organisms that do not move (Hereford, 2009). However, evidence for rapid local adaptation in mobile animals has been gathered through transplant experiments with Trinidadian guppies (Bryant et al., 2009). Sources Bowler, P.J. (1989). Evolution: The history of an idea. University of California Press. https://archive.org/details/evolutionhistory0000bowl/page/86/mode/1up. Bowler, P.J. (2003). Evolution: The history of an idea. University of California Press. https://archive.org/details/evolutionhistory0000bowl/page/86/mode/1up. Bryant, M., Gordon, S., Hendry, A., Kinnison, M., Millar, N., Räsänen, K., Reznick, D., & Weese, D. (2009). Adaptive changes in life history and survival following a new guppy introduction. The American Naturalist, 174(1), pp. 3445. doi:10.1086/599300. PMID 19438322. S2CID 8589987. Daintith, J., & Martin, E. A. (Eds.). (2010). A dictionary of science (6th ed.). Oxford University Press. p. 13. Darwin, C. (1872). Mutual affinities of organic beings: Morphology, embryology, rudimentary organs. The origin of species, (pp. 363-403). William Clowes and Sons. http://darwin-online.org.uk/content/frameset?pageseq=425&itemID=F391&viewtype=side. Desmond, A. (1989). Importing the new morphology. The politics of evolution (pp. 25-100). Library of Congress. Dobzhansky, T. (1956). Genetics of natural populations. XXV. Genetic changes in populations of Drosophila pseudoobscura and Drosophila persimilis in Some localities in California. Evolution, 10(1), pp. 82-92. doi:10.2307/2406099. JSTOR 2406099. Dobzhansky, T. (1968). On some fundamental concepts of Darwainian biology. In Dobzhansky, T., Hecht, M.K., Steere, W.C. (Eds.) Evolutionary Biology. Springer, Boston, MA. pp. 1-34 Dobzhansky, T. (1970). Genetics of the evolutionary process. Columbia University Press. pp. 4-6, 79-82 Ebert, D., & Kawecki, T.J. (2004) Conceptual issues in local adaptation. Ecology Letters, 7(12), pp. 1225-1241. doi:10.1111/j.14610248.2004.00684.x. ISSN 1461-0248. Endler, J.A. (1986). Natural selection in the wild. Princeton University Press. pp. 33-51 Fenster, C.B., & Galloway, L.F. (2000). Population differentiation in an annual legume: Local adaptation. Evolution, 54(4), pp. 1173-1181. doi:10.1111/j.0014-3820.2000.tb00552.x. ISSN 1558-5646. PMID 11005286. S2CID 13652390. Fisher, R.A. (1930). The genetical theory of natural selection. Oxford at the Clarendon Press. p. 25. Ford, E.B. (1975). Ecological genetics. Chapman & Hall. Futuyma, D.J. (1986). Evolutionary biology. Sunderland Mass. p. 552. Gaggiotti, O.E., Mouterde, M., de Villemereuil, P., Till-Bottraud, I. (2015). Common garden experiments in the genomic era: new perspectives and opportunities. Heredity, 116(3), 249-254. doi:10.1038/hdy.2015.93. PMC 4806574. PMID 26486610. Gross, R. (2012). Psychology: The science of mind and behaviour (6th ed.). Hodder. p. 335. ISBN 978-1-4441-6436-7. Hereford, J. (2009). A quantitative survey of local adaptation and fitness trade-offs. The American Naturalist, 173(5), pp. 579588. doi:10.1086/597611. ISSN 0003-0147. PMID 19272016. S2CID 524423.
Hutchinson, G. E. (1965). The ecological theater and the evolutionary play. Yale University Press. pp. 26-78. Huxley, J. (1942). Evolution: The modern synthesis. Allen & Unwin, London. Irwin, D.E., Price, T.D., Qvarnström, A. (2003). The role of phenotypic plasticity in driving genetic evolution. Proceedings of the Royal Society B, 270 (1523), pp. 1433-1440. doi:10.1098/rspb.2003.2372. PMC 1691402. PMID 12965006. Kornfield, I., & Smith, P.F. (2000). African Cichlid fishes: Model systems for evolutionary biology. Annual Review of Ecology and Systematics, 31, pp. 163-196. doi:10.1146/annurev.ecolsys.31.1.163. Mack, T., Meyer, A., Salzburger, W., Mack, T., & Verheyen, E. (2005). Out of Tanganyika: Genesis, explosive speciation, keyinnovations and phylogeography of the haplochromine cichlid fishes. BMC Evolutionary Biology, 5(17), pp. 17. doi:10.1186/14712148-5-17. PMC 554777. PMID 15723698. Margulis, L., & Fester, R. (1991). Symbiosis as a source of evolutionary innovation: Speciation and morphogenesis. MIT Press. Mayr, E. (1963). Animal species and evolution. Cambridge, Belknap Press of Harvard University Press. Mayr, E. (1982). The growth of biological thought: Diversity, evolution, and inheritance. Belknap Press. pp. 483, 562-566. Moore, L.G., & Regensteiner, J.G. (1983). Adaptation to High Altitude. Annual Review of Anthropology, 12, 285-304. doi:10.1146/annurev.an.12.100183.001441. Orr, H.A. (2005). The genetic theory of adaptation: A brief history. Nature Reviews Genetics, 6(2), 119-127. doi:10.1038/nrg1523. PMID 15716908. S2CID 17772950. Patterson, C. (1999). Evolution. Comstuck Publishing. p. 1 Pillay, N., Rymer, T., Schradin, C. (2013). Extinction or survival? Behavioral flexibility in response to environmental change in the African striped mouse Rhabdomys. Sustainability, 5(1), 163-186. doi:10.3390/su5010163. Price, P.W. (1980). The evolutionary biology of parasites. Monographs in population biology, 15. Princeton University Press. Price, T.D. (2006). Phenotypic plasticity, sexual selection and the evolution of colour patterns. The Journal of Experimental Biology, 209,(12), 2368-2376. doi:10.1242/jeb.02183. PMID 16731813. Provine, W.B. (1986). Sewall Bright and evolutionary biology. University of Chicago Press. https://archive.org/details/sewallwrightevol00will. Sejian, V., Gaughan, J., Baumgard, L., & Prasad, C. (Eds.). (2015). Climate change impact on livestock: Adaptation and mitigation. Springer. p 515. ISBN 978-81-322-2265-1 Smith, J.M. (1993). The theory of evolution. Cambridge University Press. p. 33 Sober, E. (1984). The nature of selection: Evolutionary theory in philosophical focus. MIT Press. p. 210 Stebbins, G.L. (1950). Variation and evolution in plants. Columbia University Press. Williams, C. G. (1966). Adaptation and natural selection: A critique of some current evolutionary thought. Princeton University Press. p. 5. Wang, G (2014). "Chapter 5.6--Zero Order Adaptivity". Analysis of Complex Diseases: A Mathematical Perspective. Taylor Francis. p. 69. ISBN 978-1-4665-7223-2. Wright, D.F. (1932). Proceedings of the sixth international congress of genetics. Electronic Scholarly Publishing. pp. 356-366
Wetzel from Wikipedia: https://en.wikipedia.org/wiki/Adaptation and https://en.wikipedia.org/wiki/Local_adaptation
4.1: What is adaptation? is shared under a CC BY-NC-SA license and was authored, remixed, and/or curated by LibreTexts.
4.2: Strategies for dealing with a changing environment There are lots of amazing and sometimes bizarre adaptations out there in the world. For example, some species of frogs (e.g., wood frogs) that live in temperate climates can tolerate the freezing of their blood and other tissues. These frogs allow about 65% of their bodies to freeze solid, stop breathing, and stop their heart when temperatures drop below freezing. Come spring, as temperatures rise, the frog's body thaws and basic motor functions restart, allowing these frogs to survive incredibly harsh winter conditions. Other examples of interesting adaptations include carnivorous plants that obtain their nutrients from insects (e.g., pitcher plants), or rodents (kangaroo rat) that obtain enough water from metabolism that they do not need to drink water at all.
: Frog (photo by Patti Black on Unsplash), pitcher plant (photo by Adrian Pingstone released to the public domain), and kangaroo rat (US Fish & Wildlife).
While each of these examples are fascinating in their own right, perhaps a better place to start when thinking about adaptation are the basic, or broad strategies that organisms have adapted to survive in the environment. Specifically, if we think about the fact that the environment that an organism lives in can vary considerably. The environment can vary temporally, on both short and long-term time scales, and spatially in terms of both abiotic and biotic factors. For example, the environment an organism experiences can change in temperature, precipitation, amount of sunlight, water availability, oxygen concentration, salinity, atmospheric pressure, etc. This can create problems for living things because most cellular functions (think enzymes, or neurotransmitters) require specific conditions for proper function. Biotic components of the environment can also change with time or space, including things like the availability of prey, the abundance of predators or competitors, or access to potential mates. While different groups of plants and animals may have solved different components of dealing with this variability in different ways, more broadly we can think of two basic solutions or strategies for dealing with environmental variation: conform or regulate.
Conforming is when an organism allows their internal environment to fluctuate with the external environment; we might call an organism that conforms a "conformer" for that particular environmental variable. An example of a conformer to external temperature is a frog that allows its body temperature to fluctuate with the environment (Figure A). As the external temperature increases or decreases, the internal temperature of the frog increases or decreases along with the external environment.
If we're thinking just about temperature, we often describe organisms using conforming strategies using the terms ectotherm (an animal that relies on the external environment to regulate its internal body temperature), or poikilotherm (an animal that varies its internal body temperature within a wide range of temperatures).
Figure : Basic strategies for dealing with fluctuations in the environment: conform or regulate.
Regulating is when an organism attempts to regulate or maintain a constant internal environment despite any environmental fluctuations; we might call an organism that regulates a "regulator" for that particular environmental variable. An example of a regulator for external temperature is a dog that attempts to maintain its internal body temperature within a relatively narrow range despite fluctuations in the external environment (Figure B). As the external temperature increases or decreases, the internal temperature of the dog remains nearly the same with some limitations at extreme temperatures. If we're thinking just about temperature, we often describe organisms using regulating strategies using the terms endotherm (an animal that regulates its own internal body temperature through metabolic processes), or homeotherm (maintains a constant internal body temperature, usually within a narrow range of temperatures). Some organisms can differ in their strategy for different regulatory processes. For example, salmon are thermoconformers, but osmoregulators when they move between marine (saline) and freshwater environments.. There are costs and benefits to each of these basic strategies. For example, conformers will invest less energy into maintaining their internal environment, but can experience compromised cellular functions. On the other hand, regulators can live in a wider range of environments without experiencing reduced cellular functions, but they expend a great deal of energy to maintain their internal environment (Figure ).
: Theoretical costs and benefits of an organism regulating their internal environment or conforming to the external environment.
In addition to being a conformer or regulator, organisms may also be avoiders that will escape changes in the environment by moving locally or migrating long distances (read more about this in the behavioral ecology chapter). Other types of the "avoiding" strategy could include organisms that undergo some type of dormancy, which is when an organism decreases their metabolic activity under extended unfavorable conditions in order to conserve energy.
Examples of dormancy in animals include hibernation, a mechanism used by many mammals to reduce energy expenditure and survive food shortages over the winter. During hibernation, the animal undergoes many physiological changes, including decreased heart rate (by as much as 95%) and decreased body temperature. Another type of dormancy in animals, most commonly seen in insects, is diapause, when the organism completely suspends development between autumn and spring.
In plants, dormancy is a period of arrested growth, and is a survival strategy exhibited by many plant species that allows them to survive in climates where part of the year is unsuitable for growth, such as winter or dry seasons. A classic example of dormancy in plants is seed dormancy, where seeds are prevented from germinating during unsuitable ecological conditions. Many plant species that exhibit dormancy have a biological clock that tells them when to slow activity and to prepare soft tissues for a period of
freezing temperatures or water shortage. On the other hand, dormancy can be triggered after a normal growing season by decreasing temperatures, shortened day length, and/or a reduction in rainfall. Many bacteria can survive adverse conditions such as temperature, desiccation, and antibiotics by forming endospores, cysts, or states of reduced metabolic activity lacking specialized cellular structures. For organisms that regulate components of their internal environment to big changes in the external environment, one key question we might have is: how do they do this? Mechanistically, the process of adjusting the internal environment in response to an external change is described as acclimation. Acclimation Acclimation 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 fitness across a range of environmental conditions. Acclimation occurs in a short period of time (hours to weeks), and within the organism's lifetime (compared to adaptation, which is evolution, taking 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 (The Unabridged Hutchinson Encyclopedia, 2009). 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. Methods of acclimation 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 membranes making them more fluid in cold temperatures and less fluid in warm temperatures by increasing the number of membrane proteins (Los & Murata, 2004). In response to certain stressors, some organisms express so-called heat shock proteins that act as molecular chaperones and reduce denaturation by guiding the folding 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 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) (Liknes & Swanson, 2011; McKechnie, 2008). Examples Plants Many plants, such as maple trees, irises, and tomatoes, 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 (Canejo et al., 2007). Animals Animals acclimatize in many ways. Sheep grow very thick wool in cold, damp climates. Fish are able to adjust only gradually to changes in water temperature and quality. Tropical fish sold at pet stores are often kept in acclimation bags until this process is complete. Lowe & Vance (1955) 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 (Slotsbo et al., 2016). Humans The salt content of sweat and urine decreases as people acclimatize to hot conditions (U.S. Army, 2007). Plasma volume, heart rate, and capillary activation are also affected (Heat Acclimatization, n.d.). Acclimation to high altitude continues for months or even years after initial ascent, and ultimately enables humans to survive in an environment that, without acclimation, 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 to increase the oxygen carrying capacity of the blood, in order to compensate for lower levels of oxygen intake (Muza et al., 2004; Baillie & Simpson, 2006). Sources Ali, M. B., Khatun, S., Hahn, E. J., & Paek, K. Y. (2006). Enhancement of phenylpropanoid enzymes and lignin in Phalaenopsis orchid and their influence on plant acclimatisation at different levels of photosynthetic photon flux. Plant Growth Regulation, 49(2-3), 137-146. https://doi.org/10.1007/s10725-006-9003-z Angilletta, M. J. (2009). Thermal adaptation: A theoretical and empirical synthesis. Oxford University Press. Baillie, K., & Simpson, A. (2006). Altitude oxygen calculator. Apex (Altitude Physiology EXpeditions). Archived from the original on June 11, 2017. Retrieved August 10, 2006. Camejo, D., Martí, M. C., Nicolás, E., Alarcón, J. J., Jiménez, A., & Sevilla, F. (2007). Response of superoxide dismutase isoenzymes in tomato plants (Lycopersicon esculentum) during thermo-acclimation of the photosynthetic apparatus. Physiologia Plantarum, 131(3), 367-377. https://doi.org/10.1111/j.1399-3054.2007.00953.x DeWitt, T. J., Sih, A., & Wilson, D. S. (1998). Costs and limits of phenotypic plasticity. Trends in Ecology & Evolution, 13(2), 77- 81. https://doi.org/10.1016/S0169-5347(97)01274-3 Heat acclimatization. (n.d.). Sports Science. Retrieved December 3, 2017, from http://www.sportsci.org Liknes, E. T., & Swanson, D. L. (2011). Phenotypic flexibility of body composition associated with seasonal acclimatization in passerine birds. Journal of Thermal Biology, 36(6), 363-370. https://doi.org/10.1016/j.jtherbio.2011.06.010 Los, D. A., & Murata, N. (2004) Membrane fluidity and its roles in the perception of environmental signals. Biochimica et Biophysica Acta (BBA) - Biomembranes, 1666(1-2), 142-157. https://doi.org/10.1016/j.bbamem.2004.08.002 Lowe, C. H., & Vance, V. J. (1955). Acclimation of the critical thermal maximum of the reptile Urosaurus ornatus. Science, 122(3158), 73-74. https://doi.org/10.1126/science.122.3158.73 McKechnie, A. E. (2008). Phenotypic flexibility in basal metabolic rate and the changing view of avian physiological diversity: A review. Journal of Comparative Physiology B, 178(3), 235-247. https://doi.org/10.1007/s00360-007-0218-8 Muza, S. R., Fulco, C. S., & Cymerman, A. (2004). Altitude acclimatization guide (USARIEM-TN-04-05). U.S. Army Research Institute of Environmental Medicine, Thermal and Mountain Medicine Division. Archived from the original on April 23, 2009. Retrieved March 5, 2009. Slotsbo, S., Schou, M. F., Kristensen, T. N., Loeschcke, V., & Sørensen, J. G. (2016). Reversibility of developmental heat and cold plasticity is asymmetric and has long-lasting consequences for adult thermal tolerance. Journal of Experimental Biology, 219(17), 2726-2732. https://doi.org/10.1242/jeb.143750 The Unabridged Hutchinson Encyclopedia. (2009). Acclimatisation. Retrieved November 5, 2009, from http://encyclopedia.farlex.com/acclimatization U.S. Army. (2007). Heat acclimatization guide (PDF). Archived from the original (PDF) on July 2, 2007. Retrieved July 2, 2009. Written by Dan Wetzel, and modified by Dan Wetzel from the following sources: Acclimation section from Wikipedia: https://en.wikipedia.org/wiki/Acclimatization Information on plant dormancy from: https://en.Wikipedia.org/wiki/Dormancy
4.2: Strategies for dealing with a changing environment is shared under a CC BY-NC-SA license and was authored, remixed, and/or curated by LibreTexts.
4.3: Adaptations to avoid harsh conditions The content for this subtopic is found in two external pages. Please click the links below to access this information. Extreme Cold Hardiness in Ectotherms Costanzo, J. P. (2011) Extreme Cold Hardiness in Ectotherms. Nature Education Knowledge 3(10):3 Plant-Soil Interactions: Nutrient Uptake Morgan, J. B. & Connolly, E. L. (2013) Plant-Soil Interactions: Nutrient Uptake. Nature Education Knowledge 4(8):2 4.3: Adaptations to avoid harsh conditions is shared under a CC BY-NC-SA license and was authored, remixed, and/or curated by LibreTexts.
4.4: Physiological optima and critical limits The content for this subtopic is found in an external page. Please click the link below to access this information. Physiological Optima and Critical Limits Morgan, J. B. & Connolly, E. L. (2013) Plant-Soil Interactions: Nutrient Uptake. Nature Education Knowledge 4(8):2 4.4: Physiological optima and critical limits is shared under a CC BY-NC-SA license and was authored, remixed, and/or curated by LibreTexts.