Experimental evolution
Encyclopedia
In evolutionary and experimental biology, the field of experimental evolution is concerned with testing hypotheses and theories of evolution
by use of controlled experiment
s. Evolution may be observed in the laboratory as populations adapt to new environmental conditions and/or change by such stochastic
processes as random genetic drift
. With modern molecular
tools, it is possible to pinpoint the mutation
s that selection
acts upon, what brought about the adaptations, and to find out how exactly these mutations work. Because of the large number of generation
s required for adaptation to occur, evolution experiments are typically carried out with microorganism
s such as bacteria, yeast
or virus
es. However, laboratory studies with foxes and with rodents (see below) have shown that notable adaptations can occur within as few as 10-20 generations and experiments with wild guppies
have observed adaptations within comparable numbers of generations.
varieties, maize
, or the large number of different dog
breeds. The power of human breeding to create varieties with extreme differences from a single species was already recognized by Charles Darwin
. In fact, he started out his book The Origin of Species
with a chapter on variation in domestic animals. In this chapter, Darwin discussed in particular the pigeon. He wrote:
One of the first to carry out a controlled evolution experiment was William Dallinger
. In the late 19th century, he cultivated small unicellular organism
s in a custom-built incubator over a time period of seven years (1880–1886). Dallinger slowly increased the temperature of the incubator from an initial 60 °F up to 158 °F. The early cultures had shown clear signs of distress at a temperature of 73 °F, and were certainly not capable of surviving at 158 °F. The organisms Dallinger had in his incubator at the end of the experiment, on the other hand, were perfectly fine at 158 °F. However, these organisms would no longer grow at the initial 60 °F. Dallinger concluded that he had found evidence for Darwinian adaptation in his incubator, and that the organisms had adapted to live in a high-temperature environment. Unfortunately, Dallinger's incubator was accidentally destroyed in 1886, and Dallinger could not continue this line of research.
. Like other experimental research in evolutionary biology during this period, much of this work lacked extensive replication and was carried out only for relatively short periods of evolutionary time.
But by 1980, a variety of evolutionary biologists realized that the key to successful experimentation lay in extensive parallel replication of evolving lineages as well as a larger number of generations of selection. One of the first of a new wave of experiments using this strategy was the laboratory "evolutionary radiation" of Drosophila melanogaster
populations that Michael R. Rose started in February, 1980. This system started with ten populations, five cultured at later ages, and five cultured at early ages. Since then more than 200 different populations have been created in this laboratory radiation, with selection targeting multiple characters. Some of these highly differentiated populations have also been selected "backward" or "in reverse," by returning experimental populations to their ancestral culture regime. Hundreds of people have worked with these populations over the better part of three decades. Much of this work is summarized in the papers collected in the book Methuselah Flies, listed below.
started a long-term evolution experiment
with the bacterium E. coli. The experiment continues to this day, and is by now probably the largest controlled evolution experiment ever undertaken. Since the inception of the experiment, the bacteria have grown for more than 50,000 generations. Lenski and colleagues regularly publish updates on the status of the experiments.
and colleagues started a long-term experiment that involves selective breeding for high voluntary activity levels on running wheels. This experiment also continues to this day (> 50 generations). Mice from the four replicate "High Runner" lines evolved to run 3 times as many running-wheel revolutions per day as compared with the four unselected control mice groups, mainly by running faster than the control mice rather than running for more minutes/day.
The HR mice exhibit an elevated maximal aerobic capacity when tested on a motorized treadmill and a variety of other traits that appear to be adaptations that facilitate high levels of sustained endurance
running (e.g., larger heart
s, more symmetrical
hindlimb bones). They also exhibit alterations in motivation
and the reward system
of the brain
. Pharmacological studies point to alterations in dopamine
function and the endocannabinoid system
. The High Runner lines have been proposed as a model to study human attention-deficit hyperactivity disorder (ADHD), and administration of Ritalin reduces their wheel running approximately to the levels of Control mice. Click here for a mouse wheel running video.
fish have both marine and freshwater species, the freshwater species evolving since the last ice age. Fresh water species can survive colder temperatures. Scientists tested to see if they could reproduce this evolution of cold-tolerance by keeping marine sticklebacks in cold freshwater. It took the marine sticklebacks only three generations to evolve to match the 2.5 degree celsius improvement in cold-tolerance found in wild freshwater sticklebacks. http://rspb.royalsocietypublishing.org/content/early/2010/07/29/rspb.2010.0923.full
Evolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...
by use of controlled experiment
Experiment
An experiment is a methodical procedure carried out with the goal of verifying, falsifying, or establishing the validity of a hypothesis. Experiments vary greatly in their goal and scale, but always rely on repeatable procedure and logical analysis of the results...
s. Evolution may be observed in the laboratory as populations adapt to new environmental conditions and/or change by such stochastic
Stochastic
Stochastic refers to systems whose behaviour is intrinsically non-deterministic. A stochastic process is one whose behavior is non-deterministic, in that a system's subsequent state is determined both by the process's predictable actions and by a random element. However, according to M. Kac and E...
processes as random genetic drift
Genetic drift
Genetic drift or allelic drift is the change in the frequency of a gene variant in a population due to random sampling.The alleles in the offspring are a sample of those in the parents, and chance has a role in determining whether a given individual survives and reproduces...
. With modern molecular
Molecular biology
Molecular biology is the branch of biology that deals with the molecular basis of biological activity. This field overlaps with other areas of biology and chemistry, particularly genetics and biochemistry...
tools, it is possible to pinpoint the mutation
Mutation
In molecular biology and genetics, mutations are changes in a genomic sequence: the DNA sequence of a cell's genome or the DNA or RNA sequence of a virus. They can be defined as sudden and spontaneous changes in the cell. Mutations are caused by radiation, viruses, transposons and mutagenic...
s that selection
Selection
In the context of evolution, certain traits or alleles of genes segregating within a population may be subject to selection. Under selection, individuals with advantageous or "adaptive" traits tend to be more successful than their peers reproductively—meaning they contribute more offspring to the...
acts upon, what brought about the adaptations, and to find out how exactly these mutations work. Because of the large number of generation
Generation
Generation , also known as procreation in biological sciences, is the act of producing offspring....
s required for adaptation to occur, evolution experiments are typically carried out with microorganism
Microorganism
A microorganism or microbe is a microscopic organism that comprises either a single cell , cell clusters, or no cell at all...
s such as bacteria, yeast
Yeast
Yeasts are eukaryotic micro-organisms classified in the kingdom Fungi, with 1,500 species currently described estimated to be only 1% of all fungal species. Most reproduce asexually by mitosis, and many do so by an asymmetric division process called budding...
or virus
Virus
A virus is a small infectious agent that can replicate only inside the living cells of organisms. Viruses infect all types of organisms, from animals and plants to bacteria and archaea...
es. However, laboratory studies with foxes and with rodents (see below) have shown that notable adaptations can occur within as few as 10-20 generations and experiments with wild guppies
Guppy
The guppy , also known as the millionfish, is one of the most popular freshwater aquarium fish species in the world. It is a small member of the Poeciliidae family [females long, males long] and like all other members of the family, is live-bearing....
have observed adaptations within comparable numbers of generations.
Evolution experiments throughout human history
Unwittingly, humans have carried out evolution experiments for as long as they have been domesticating plants and animals. Selective breeding of plants and animals has led to varieties that differ dramatically from their original wild-type ancestors. Examples are the cabbageCabbage
Cabbage is a popular cultivar of the species Brassica oleracea Linne of the Family Brassicaceae and is a leafy green vegetable...
varieties, maize
Maize
Maize known in many English-speaking countries as corn or mielie/mealie, is a grain domesticated by indigenous peoples in Mesoamerica in prehistoric times. The leafy stalk produces ears which contain seeds called kernels. Though technically a grain, maize kernels are used in cooking as a vegetable...
, or the large number of different dog
Dog
The domestic dog is a domesticated form of the gray wolf, a member of the Canidae family of the order Carnivora. The term is used for both feral and pet varieties. The dog may have been the first animal to be domesticated, and has been the most widely kept working, hunting, and companion animal in...
breeds. The power of human breeding to create varieties with extreme differences from a single species was already recognized by Charles Darwin
Charles Darwin
Charles Robert Darwin FRS was an English naturalist. He established that all species of life have descended over time from common ancestry, and proposed the scientific theory that this branching pattern of evolution resulted from a process that he called natural selection.He published his theory...
. In fact, he started out his book The Origin of Species
The Origin of Species
Charles Darwin's On the Origin of Species, published on 24 November 1859, is a work of scientific literature which is considered to be the foundation of evolutionary biology. Its full title was On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the...
with a chapter on variation in domestic animals. In this chapter, Darwin discussed in particular the pigeon. He wrote:
Early experimental evolution
William Dallinger
Rev. Dr. William Henry Dallinger F.R.S. was a British minister in the Wesleyan Methodist Church. He was also an accomplished scientist, being the first to study the complete lifecycle of unicellular organisms under the microscope and studying the adaptation of such organisms to temperature.He made...
. In the late 19th century, he cultivated small unicellular organism
Unicellular organism
A unicellular organism, also known as a single-celled organism is an organism that consists of only one cell, in contrast to a multicellular organism that consists of multiple cells. Historically simple single celled organisms have sometimes been referred to as monads Prokaryotes, most protists,...
s in a custom-built incubator over a time period of seven years (1880–1886). Dallinger slowly increased the temperature of the incubator from an initial 60 °F up to 158 °F. The early cultures had shown clear signs of distress at a temperature of 73 °F, and were certainly not capable of surviving at 158 °F. The organisms Dallinger had in his incubator at the end of the experiment, on the other hand, were perfectly fine at 158 °F. However, these organisms would no longer grow at the initial 60 °F. Dallinger concluded that he had found evidence for Darwinian adaptation in his incubator, and that the organisms had adapted to live in a high-temperature environment. Unfortunately, Dallinger's incubator was accidentally destroyed in 1886, and Dallinger could not continue this line of research.
Modern experimental evolution
From the 1880s to 1980, experimental evolution was intermittently practiced by a variety of evolutionary biologists, including the highly influential Theodosius DobzhanskyTheodosius Dobzhansky
Theodosius Grygorovych Dobzhansky ForMemRS was a prominent geneticist and evolutionary biologist, and a central figure in the field of evolutionary biology for his work in shaping the unifying modern evolutionary synthesis...
. Like other experimental research in evolutionary biology during this period, much of this work lacked extensive replication and was carried out only for relatively short periods of evolutionary time.
But by 1980, a variety of evolutionary biologists realized that the key to successful experimentation lay in extensive parallel replication of evolving lineages as well as a larger number of generations of selection. One of the first of a new wave of experiments using this strategy was the laboratory "evolutionary radiation" of Drosophila melanogaster
Drosophila 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...
populations that Michael R. Rose started in February, 1980. This system started with ten populations, five cultured at later ages, and five cultured at early ages. Since then more than 200 different populations have been created in this laboratory radiation, with selection targeting multiple characters. Some of these highly differentiated populations have also been selected "backward" or "in reverse," by returning experimental populations to their ancestral culture regime. Hundreds of people have worked with these populations over the better part of three decades. Much of this work is summarized in the papers collected in the book Methuselah Flies, listed below.
Lenski's long-term evolution experiment with Escherichia coli
On February 15, 1988, Richard LenskiRichard 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...
started a long-term evolution experiment
E. coli long-term evolution experiment
The E. coli long-term evolution experiment is an ongoing study in experimental evolution led by Richard Lenski that has been tracking genetic changes in 12 initially identical populations of asexual Escherichia coli bacteria since 24 February 1988...
with the bacterium E. coli. The experiment continues to this day, and is by now probably the largest controlled evolution experiment ever undertaken. Since the inception of the experiment, the bacteria have grown for more than 50,000 generations. Lenski and colleagues regularly publish updates on the status of the experiments.
Garland's long-term experiment with laboratory house mice
In 1993, Theodore Garland, Jr.Theodore Garland, Jr.
Theodore Garland, Jr. is a biologist specializing in evolutionary physiology. He was on the faculty at the University of Wisconsin–Madison for 14 years, served at the National Science Foundation for one year, and is currently Professor of Biology at the University of California, Riverside. He...
and colleagues started a long-term experiment that involves selective breeding for high voluntary activity levels on running wheels. This experiment also continues to this day (> 50 generations). Mice from the four replicate "High Runner" lines evolved to run 3 times as many running-wheel revolutions per day as compared with the four unselected control mice groups, mainly by running faster than the control mice rather than running for more minutes/day.
The HR mice exhibit an elevated maximal aerobic capacity when tested on a motorized treadmill and a variety of other traits that appear to be adaptations that facilitate high levels of sustained endurance
Endurance
Endurance is the ability for a human or animal to exert itself and remain active for a long period of time, as well as its ability to resist, withstand, recover from, and have immunity to trauma, wounds, or fatigue. In humans, it is usually used in aerobic or anaerobic exercise...
running (e.g., larger heart
Heart
The heart is a myogenic muscular organ found in all animals with a circulatory system , that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions...
s, more symmetrical
Symmetry (biology)
Symmetry in biology is the balanced distribution of duplicate body parts or shapes. The body plans of most multicellular organisms exhibit some form of symmetry, either radial symmetry or bilateral symmetry or "spherical symmetry". A small minority exhibit no symmetry .In nature and biology,...
hindlimb bones). They also exhibit alterations in motivation
Motivation
Motivation is the driving force by which humans achieve their goals. Motivation is said to be intrinsic or extrinsic. The term is generally used for humans but it can also be used to describe the causes for animal behavior as well. This article refers to human motivation...
and the reward system
Reward system
In neuroscience, the reward system is a collection of brain structures which attempts to regulate and control behavior by inducing pleasurable effects...
of the brain
Brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
. Pharmacological studies point to alterations in dopamine
Dopamine
Dopamine is a catecholamine neurotransmitter present in a wide variety of animals, including both vertebrates and invertebrates. In the brain, this substituted phenethylamine functions as a neurotransmitter, activating the five known types of dopamine receptors—D1, D2, D3, D4, and D5—and their...
function and the endocannabinoid system
Endocannabinoid system
The endocannabinoid system refers to a group of neuromodulatory lipids and their receptors that are involved in a variety of physiological processes including appetite, pain-sensation, mood, and memory; it mediates the psychoactive effects of cannabis and, broadly speaking, includes:* The...
. The High Runner lines have been proposed as a model to study human attention-deficit hyperactivity disorder (ADHD), and administration of Ritalin reduces their wheel running approximately to the levels of Control mice. Click here for a mouse wheel running video.
Other examples
SticklebackStickleback
The Gasterosteidae are a family of fish including the sticklebacks. FishBase currently recognises sixteen species in the family, grouped in five genera. However several of the species have a number of recognised subspecies, and the taxonomy of the family is thought to be in need of revision...
fish have both marine and freshwater species, the freshwater species evolving since the last ice age. Fresh water species can survive colder temperatures. Scientists tested to see if they could reproduce this evolution of cold-tolerance by keeping marine sticklebacks in cold freshwater. It took the marine sticklebacks only three generations to evolve to match the 2.5 degree celsius improvement in cold-tolerance found in wild freshwater sticklebacks. http://rspb.royalsocietypublishing.org/content/early/2010/07/29/rspb.2010.0923.full
See also
- Artificial selectionArtificial selectionArtificial selection describes intentional breeding for certain traits, or combination of traits. The term was utilized by Charles Darwin in contrast to natural selection, in which the differential reproduction of organisms with certain traits is attributed to improved survival or reproductive...
- DomesticationDomesticationDomestication or taming is the process whereby a population of animals or plants, through a process of selection, becomes accustomed to human provision and control. In the Convention on Biological Diversity a domesticated species is defined as a 'species in which the evolutionary process has been...
- Evolutionary biology
- 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...
- GeneticsGeneticsGenetics , a discipline of biology, is the science of genes, heredity, and variation in living organisms....
- Genomics of domesticationGenomics of domesticationGenomics is the study of the structure, content, and evolution of genomes, or the entire genetic information of organisms. Domestication is the process by which humans alter the morphology and genes of targeted organisms in order to select for desirable traits.-Background:Since Domestication...
- Quantitative geneticsQuantitative geneticsQuantitative genetics is the study of continuous traits and their underlying mechanisms. It is effectively an extension of simple Mendelian inheritance in that the combined effects of one or more genes and the environments in which they are expressed give rise to continuous distributions of...
- Selective breedingSelective breedingSelective breeding is the process of breeding plants and animals for particular genetic traits. Typically, strains that are selectively bred are domesticated, and the breeding is sometimes done by a professional breeder. Bred animals are known as breeds, while bred plants are known as varieties,...
- Tame Silver FoxTame Silver FoxThe domesticated silver fox is a domesticated form of the silver morph of the red fox. As a result of selective breeding, the new foxes became not only tamer, but more dog-like as well....
Further reading
- Dallinger, W. H. 1887. The president's address. J. Roy. Microscop. Soc., 185-199.
- Elena, S. F., and R. E. Lenski. 2003. Evolution experiments with microorganisms: the dynamics and genetic bases of adaptation. Nature Reviews Genetics 4: 457-469.
- Garland, T., Jr. 2003. Selection experiments: an under-utilized tool in biomechanics and organismal biology. Pages 23–56 in V. L. Bels, J.-P. Gasc, A. Casinos, eds. Vertebrate biomechanics and evolution. BIOS Scientific PublishersBIOS Scientific PublishersBIOS Scientific Publishers was an English publisher. The main offices were based at Milton Park near Abingdon, Oxfordshire, south of Oxford, England. The company specialised in biosciences....
, Oxford, UK. PDF - Garland, T., Jr., and M. R. Rose, eds. 2009. Experimental evolution: concepts, methods, and applications of selection experiments. University of California Press, Berkeley, California. PDF of Table of Contents
- Gibbs, A. G. 1999. Laboratory selection for the comparative physiologist. Journal of Experimental Biology 202: 2709-2718.
- Lenski, R. E. 2004. Phenotypic and genomic evolution during a 20,000-generation experiment with the bacterium Escherichia coli. Plant Breeding Reviews 24: 225-265.
- Lenski, R. E., M. R. Rose, S. C. Simpson, and S. C. Tadler. 1991. Long-term experimental evolution in Escherichia coli. I. Adaptation and divergence during 2,000 generations. American Naturalist 138: 1315-1341.
- McKenzie, J. A., and P. Batterham. 1994. The genetic, molecular and phenotypic consequences of selection for insecticide resistance. Trends in Ecology and Evolution 9: 166-169.
- Reznick, D. N., M. J. Bryant, D. Roff, C. K. Ghalambor, and D. E. Ghalambor. 2004. Effect of extrinsic mortality on the evolution of senescence in guppies. Nature 431: 1095-1099.
- Rose, M. R., H. B. Passananti, and M. Matos, eds. 2004. Methuselah flies: A case study in the evolution of aging. World Scientific Publishing, Singapore.
- Swallow, J. G., and T. Garland, Jr. 2005. Selection experiments as a tool in evolutionary and comparative physiology: insights into complex traits — An introduction to the symposium. Integrative and Comparative Biology 45: 387-390. PDF
External links
- E. coli Long-term Experimental Evolution Project Site, Lenski lab, Michigan State UniversityMichigan State UniversityMichigan State University is a public research university in East Lansing, Michigan, USA. Founded in 1855, it was the pioneer land-grant institution and served as a model for future land-grant colleges in the United States under the 1862 Morrill Act.MSU pioneered the studies of packaging,...
- A movie illustrating the dramatic differences in wheel-running behavior.
- Experimental Evolution Publications by Ted Garland: Artificial Selection for High Voluntary Wheel-Running Behavior in House Mice — a detailed list of publications.
- Experimental Evolution — a list of laboratories that study experimental evolution.
- Network for Experimental Research on Evolution, University of CaliforniaUniversity of CaliforniaThe University of California is a public university system in the U.S. state of California. Under the California Master Plan for Higher Education, the University of California is a part of the state's three-tier public higher education system, which also includes the California State University...
. - New Scientist article on domestication by selection