Beneficial acclimation hypothesis
Encyclopedia
The Beneficial Acclimation Hypothesis (BAH) is the physiological
hypothesis
that acclimating to a particular environment (usually thermal) provides an organism
with advantages in that environment. First formally defined and tested by Armand Marie Leroi
, Albert Bennett, and Richard Lenski
in 1994, it has however been a central assumption in historical physiological work that acclimation is adaptive. Further refined by Raymond B. Huey
and David Berrigan under the strong inference
approach, the hypothesis has been falsified
as a general rule by a series of multiple hypotheses experiments.
responses that occurs during an individual’s lifetime to chronic laboratory-induced environmental conditions (in contrast to acclimatization
). It is one component of adaptation
. While physiologists have traditionally assumed that acclimation is beneficial (or explicitly defined it as such), criticism of the adaptationist program by Stephen Jay Gould
and Richard Lewontin
led to a call for increased robustness in testing adaptationist hypotheses.
The initial definition of the BAH, as published in 1994 in the Proceedings of the National Academy of Sciences by Leroi et al., is that
approach, multiple competing hypotheses were needed to properly assess beneficial acclimation (see picture at right). These included:
and Escherichia coli
. More specifically, experimental tests have centered on easily-measured temperature adaptation (although other systems have been studied; see ). Of the several experimental tests of the Beneficial Acclimation Hypothesis, most have rejected it as a universal rule (see reviews ).
Initial experiments by Leroi et al., the first scientists to address this problem, tested only the Beneficial Acclimation Hypothesis and not the subsequent hypotheses developed by Huey et al. Colonies of E. coli were acclimated for seven generations in two different temperature conditions: 32 °C and 41.5 °C. Colonies were then competed against each other at those temperatures. He found that, agreeing with the Beneficial Acclimation Hypothesis, colonies acclimated at 32 °C competed better at 32 °C. However, at 41.5 °C, colonies acclimated at 32 °C competed better as well. This led to the authors’ rejection of the generality of beneficial acclimation.
Huey et al. examined four previously-conducted studies, applying the five competing hypotheses, and found that none of the results of the studies could be entirely explained by beneficial acclimation. Instead, a combination of hypotheses were required to explain the observed patterns of acclimation.
paper. They suggested that:
traits. The study of developmental and phenotypic plasticity
continues.
Physiology
Physiology is the science of the function of living systems. This includes how organisms, organ systems, organs, cells, and bio-molecules carry out the chemical or physical functions that exist in a living system. The highest honor awarded in physiology is the Nobel Prize in Physiology or...
hypothesis
Hypothesis
A hypothesis is a proposed explanation for a phenomenon. The term derives from the Greek, ὑποτιθέναι – hypotithenai meaning "to put under" or "to suppose". For a hypothesis to be put forward as a scientific hypothesis, the scientific method requires that one can test it...
that acclimating to a particular environment (usually thermal) provides an organism
Organism
In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...
with advantages in that environment. First formally defined and tested by Armand Marie Leroi
Armand Marie Leroi
Armand Marie Leroi is an evolutionary developmental biologist at Imperial College in London. A Dutch citizen, his youth was spent in New Zealand, South Africa and Canada. He was awarded a BSc. by Dalhousie University, Halifax, Canada in 1989, and a Ph.D. by the University of California, Irvine in...
, Albert Bennett, and Richard Lenski
Richard Lenski
Richard E. Lenski is an American evolutionary biologist. He is the son of sociologist Gerhard Lenski. He earned his BA from Oberlin College in 1976, and his PhD from the University of North Carolina in 1982...
in 1994, it has however been a central assumption in historical physiological work that acclimation is adaptive. Further refined by Raymond B. Huey
Raymond B. Huey
Raymond B. Huey is a biologist specializing in evolutionary physiology. He has taught at the University of Washington , and he earned his Ph.D. in biology at Harvard University under E. E. Williams. He is currently the chairman of the UW Biology Department.-Education:Huey earned his A.B...
and David Berrigan under the strong inference
Strong inference
In philosophy of science, strong inference is a model of scientific inquiry that emphasises the need for alternative hypotheses, rather than a single hypothesis in order to avoid confirmation bias....
approach, the hypothesis has been falsified
Falsification
Falsification may refer to:* The act of disproving a proposition, hypothesis, or theory: see Falsifiability* Mathematical proof* Falsified evidence...
as a general rule by a series of multiple hypotheses experiments.
History and Definition
Acclimation is a set of physiologicalPhysiology
Physiology is the science of the function of living systems. This includes how organisms, organ systems, organs, cells, and bio-molecules carry out the chemical or physical functions that exist in a living system. The highest honor awarded in physiology is the Nobel Prize in Physiology or...
responses that occurs during an individual’s lifetime to chronic laboratory-induced environmental conditions (in contrast to acclimatization
Acclimatization
Acclimatisation or acclimation is the process of an individual organism adjusting to a gradual change in its environment, allowing it to maintain performance across a range of environmental conditions...
). It is one component of adaptation
Adaptation
An adaptation in biology is a trait with a current functional role in the life history of an organism that is maintained and evolved by means of natural selection. An adaptation refers to both the current state of being adapted and to the dynamic evolutionary process that leads to the adaptation....
. While physiologists have traditionally assumed that acclimation is beneficial (or explicitly defined it as such), criticism of the adaptationist program by Stephen Jay Gould
Stephen Jay Gould
Stephen Jay Gould was an American paleontologist, evolutionary biologist, and historian of science. He was also one of the most influential and widely read writers of popular science of his generation....
and Richard Lewontin
Richard Lewontin
Richard Charles "Dick" Lewontin is an American evolutionary biologist, geneticist and social commentator. A leader in developing the mathematical basis of population genetics and evolutionary theory, he pioneered the notion of using techniques from molecular biology such as gel electrophoresis to...
led to a call for increased robustness in testing adaptationist hypotheses.
The initial definition of the BAH, as published in 1994 in the Proceedings of the National Academy of Sciences by Leroi et al., is that
“acclimation to a particular environment gives an organism a performance advantage in that environment over another organism that has not had the opportunity to acclimate to that particular environment.”This definition was further reworked in an article in American Zoologist 1999 by Raymond B. Huey, David Berrigan, George W. Gilchrist, and Jon C. Herron. They determined that, following Platt’s strong inference
Strong inference
In philosophy of science, strong inference is a model of scientific inquiry that emphasises the need for alternative hypotheses, rather than a single hypothesis in order to avoid confirmation bias....
approach, multiple competing hypotheses were needed to properly assess beneficial acclimation (see picture at right). These included:
1. Beneficial Acclimation. Acclimating to a particular environment confers fitnessFitness (biology)Fitness is a central idea in evolutionary theory. It can be defined either with respect to a genotype or to a phenotype in a given environment...
advantages in that environment.
2. Optimal Developmental Temperature. There is an ideal temperature to develop at so individuals reared at an optimal temperature compete better in all environments.
3. Colder (bigger) Is Better. In ectotherms, individuals reared in colder environments tend to develop to a larger body size. These individuals therefore have a fitnessFitness (biology)Fitness is a central idea in evolutionary theory. It can be defined either with respect to a genotype or to a phenotype in a given environment...
advantage in all environments.
4. Warmer (smaller) Is Better. The inverse of Colder Is Better. Smaller individuals have a fitnessFitness (biology)Fitness is a central idea in evolutionary theory. It can be defined either with respect to a genotype or to a phenotype in a given environment...
advantage.
5. Developmental Buffering. Development temperature does not affect adult fitnessFitness (biology)Fitness is a central idea in evolutionary theory. It can be defined either with respect to a genotype or to a phenotype in a given environment...
.
Experimental Tests
The majority of tests of the Beneficial Adaptation Hypothesis have, following Krogh's Principle, centered on the model organisms Drosophila melanogasterDrosophila melanogaster
Drosophila melanogaster is a species of Diptera, or the order of flies, in the family Drosophilidae. The species is known generally as the common fruit fly or vinegar fly. Starting from Charles W...
and Escherichia coli
Escherichia coli
Escherichia coli is a Gram-negative, rod-shaped bacterium that is commonly found in the lower intestine of warm-blooded organisms . Most E. coli strains are harmless, but some serotypes can cause serious food poisoning in humans, and are occasionally responsible for product recalls...
. More specifically, experimental tests have centered on easily-measured temperature adaptation (although other systems have been studied; see ). Of the several experimental tests of the Beneficial Acclimation Hypothesis, most have rejected it as a universal rule (see reviews ).
Initial experiments by Leroi et al., the first scientists to address this problem, tested only the Beneficial Acclimation Hypothesis and not the subsequent hypotheses developed by Huey et al. Colonies of E. coli were acclimated for seven generations in two different temperature conditions: 32 °C and 41.5 °C. Colonies were then competed against each other at those temperatures. He found that, agreeing with the Beneficial Acclimation Hypothesis, colonies acclimated at 32 °C competed better at 32 °C. However, at 41.5 °C, colonies acclimated at 32 °C competed better as well. This led to the authors’ rejection of the generality of beneficial acclimation.
Huey et al. examined four previously-conducted studies, applying the five competing hypotheses, and found that none of the results of the studies could be entirely explained by beneficial acclimation. Instead, a combination of hypotheses were required to explain the observed patterns of acclimation.
Why Is Acclimation Not Beneficial?
While it seems intuitive that acclimation would provide benefits to individuals, the majority of empirical tests of the hypothesis have rejected its general appliction. Why then is acclimation not beneficial? H. Arthur Woods and Jon F. Harrison examined the possible reasons in a 2002 EvolutionEvolution (journal)
Evolution, the International Journal of Organic Evolution, is a leading monthly scientific journal that publishes significant new results of empirical or theoretical investigations concerning facts, processes, mechanics, or concepts of evolutionary phenomena and events. Evolution is published by...
paper. They suggested that:
1. The timescale of adaptationAdaptationAn adaptation in biology is a trait with a current functional role in the life history of an organism that is maintained and evolved by means of natural selection. An adaptation refers to both the current state of being adapted and to the dynamic evolutionary process that leads to the adaptation....
is much longer than that of environmental variation.
2. Environmental cues for timing of adaptive acclimation are unreliable.
3. It may cost more to adapt than not to.
4. Migration by adjacent populations may swamp out genesGênesGênes is the name of a département of the First French Empire in present Italy, named after the city of Genoa. It was formed in 1805, when Napoleon Bonaparte occupied the Republic of Genoa. Its capital was Genoa, and it was divided in the arrondissements of Genoa, Bobbio, Novi Ligure, Tortona and...
for adaptive acclimation.
Criticism
In response to continuing rejections of the Beneficial Acclimation Hypothesis, a number of common criticisms of experimental tests have been developed:1. The majority of studies have actually been examining developmental acclimation. That is, rather than acclimating an adult individual and testing, they suggest that developmental switches triggered by particular temperatures result in a different mechanism of acclimation. More recently, it has been found that adult acclimation and developmental acclimation lead to support for different hypotheses.
2. Most studies have included stressful temperatures. Acclimation to those temperatures may decrease fitnessFitness (biology)Fitness is a central idea in evolutionary theory. It can be defined either with respect to a genotype or to a phenotype in a given environment...
in an individual.
3. Finally, a variety of traits are examined in these studies that may only be indirectly linked to fitness. For example, examining longevityLongevityThe word "longevity" is sometimes used as a synonym for "life expectancy" in demography or known as "long life", especially when it concerns someone or something lasting longer than expected ....
as a fitnessFitness (biology)Fitness is a central idea in evolutionary theory. It can be defined either with respect to a genotype or to a phenotype in a given environment...
measure in D. melanogaster may be irrelevant since fertilityFertilityFertility is the natural capability of producing offsprings. As a measure, "fertility rate" is the number of children born per couple, person or population. Fertility differs from fecundity, which is defined as the potential for reproduction...
declines rapidly with age in this species.
Current State
The majority of studies have concluded the Beneficial Acclimation Hypothesis is not true in all cases, and that alternate hypotheses should be tested. In addition to this, recent studies of the hypothesis have provided additional complications, such as trade-offs evident only in field environments and interactions with behavior and life historyBiological life cycle
A life cycle is a period involving all different generations of a species succeeding each other through means of reproduction, whether through asexual reproduction or sexual reproduction...
traits. The study of developmental and phenotypic plasticity
Phenotypic plasticity
Phenotypic plasticity is the ability of an organism to change its phenotype in response to changes in the environment. Such plasticity in some cases expresses as several highly morphologically distinct results; in other cases, a continuous norm of reaction describes the functional interrelationship...
continues.
See also
- Acclimatisation
- AdaptationAdaptationAn adaptation in biology is a trait with a current functional role in the life history of an organism that is maintained and evolved by means of natural selection. An adaptation refers to both the current state of being adapted and to the dynamic evolutionary process that leads to the adaptation....
- EcophysiologyEcophysiologyEcophysiology or environmental physiology is a biological discipline which studies the adaptation of organism's physiology to environmental conditions...
- Evolutionary physiologyEvolutionary physiologyEvolutionary physiology is the study of physiological evolution, which is to say, the manner in which the functional characteristics of individuals in a population of organisms have responded to selection across multiple generations during the history of the population.It is a subdiscipline of both...
- FitnessFitness (biology)Fitness is a central idea in evolutionary theory. It can be defined either with respect to a genotype or to a phenotype in a given environment...
- PhysiologyPhysiologyPhysiology is the science of the function of living systems. This includes how organisms, organ systems, organs, cells, and bio-molecules carry out the chemical or physical functions that exist in a living system. The highest honor awarded in physiology is the Nobel Prize in Physiology or...