Krogh Principle
Encyclopedia
Krogh's principle states that "for such a large number of problems there will be some animal of choice, or a few such animals, on which it can be most conveniently studied." This concept is central to those disciplines of biology
that rely on the comparative method
, such as neuroethology
, comparative physiology
, and more recently functional genomics
.
, winner of the Nobel Prize
in Physiology
for his contributions to understanding the anatomy and physiology of the capillary system
. This principle first emerges in a 1929 treatise on the then current 'status' of physiology. In this article, Krogh puts forward the following opinion (emphasis added):
It should be noted, however, that nearly 60 years before August Krogh, this principle was put into words by Claude Bernard
, the French instigator of experimental medicine. In his "Introduction à l'étude de la médecine expérimentale" he stated (page 27; emphasis added):
"Krogh's principle" was not utilized as a formal term until 1975 when the biochemist Hans Adolf Krebs
(who initially described the Citric Acid Cycle
), first referred to it.
More recently, at the International Society for Neuroethology meeting in Nyborg
, Denmark
in 2004, Krogh's principle was cited as a central principle by the group at their 7th Congress. Krogh's principle has also been receiving attention in the area of functional genomics
, where there has been increasing pressure and desire to expand genomics research to a more wide variety of organisms beyond the traditional scope of the field.
, some of which are highly specialized for solving particular biological problems. These adaptations are typically exploited by biologists in several ways:
Biology
Biology is a natural science concerned with the study of life and living organisms, including their structure, function, growth, origin, evolution, distribution, and taxonomy. Biology is a vast subject containing many subdivisions, topics, and disciplines...
that rely on the comparative method
Comparative method
In linguistics, the comparative method is a technique for studying the development of languages by performing a feature-by-feature comparison of two or more languages with common descent from a shared ancestor, as opposed to the method of internal reconstruction, which analyzes the internal...
, such as neuroethology
Neuroethology
Neuroethology is the evolutionary and comparative approach to the study of animal behavior and its underlying mechanistic control by the nervous system...
, comparative physiology
Comparative physiology
Comparative physiology is a subdiscipline of physiology that studies and exploits the diversity of functional characteristics of various kinds of organisms. It is closely related to evolutionary physiology and environmental physiology. Many universities offer undergraduate courses that cover...
, and more recently functional genomics
Functional genomics
Functional genomics is a field of molecular biology that attempts to make use of the vast wealth of data produced by genomic projects to describe gene functions and interactions...
.
History
Krogh's principle is attributed to Danish physiologist August KroghAugust Krogh
Schack August Steenberg Krogh FRS was a Danish professor of Romani background at the department of zoophysiology at the University of Copenhagen from 1916-1945...
, winner of the Nobel Prize
Nobel Prize
The Nobel Prizes are annual international awards bestowed by Scandinavian committees in recognition of cultural and scientific advances. The will of the Swedish chemist Alfred Nobel, the inventor of dynamite, established the prizes in 1895...
in Physiology
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...
for his contributions to understanding the anatomy and physiology of the capillary system
Capillary
Capillaries are the smallest of a body's blood vessels and are parts of the microcirculation. They are only 1 cell thick. These microvessels, measuring 5-10 μm in diameter, connect arterioles and venules, and enable the exchange of water, oxygen, carbon dioxide, and many other nutrient and waste...
. This principle first emerges in a 1929 treatise on the then current 'status' of physiology. In this article, Krogh puts forward the following opinion (emphasis added):
It should be noted, however, that nearly 60 years before August Krogh, this principle was put into words by Claude Bernard
Claude Bernard
Claude Bernard was a French physiologist. He was the first to define the term milieu intérieur . Historian of science I. Bernard Cohen of Harvard University called Bernard "one of the greatest of all men of science"...
, the French instigator of experimental medicine. In his "Introduction à l'étude de la médecine expérimentale" he stated (page 27; emphasis added):
"Krogh's principle" was not utilized as a formal term until 1975 when the biochemist Hans Adolf Krebs
Hans Adolf Krebs
Sir Hans Adolf Krebs was a German-born British physician and biochemist. Krebs is best known for his identification of two important metabolic cycles: the urea cycle and the citric acid cycle...
(who initially described the Citric Acid Cycle
Citric acid cycle
The citric acid cycle — also known as the tricarboxylic acid cycle , the Krebs cycle, or the Szent-Györgyi-Krebs cycle — is a series of chemical reactions which is used by all aerobic living organisms to generate energy through the oxidization of acetate derived from carbohydrates, fats and...
), first referred to it.
More recently, at the International Society for Neuroethology meeting in Nyborg
Nyborg
Nyborg is a city in central Denmark, located in Nyborg Municipality on the island of Funen and with a population of 16,492 . Nyborg is one of the 14 large municipalities created on 1 January 2007...
, Denmark
Denmark
Denmark is a Scandinavian country in Northern Europe. The countries of Denmark and Greenland, as well as the Faroe Islands, constitute the Kingdom of Denmark . It is the southernmost of the Nordic countries, southwest of Sweden and south of Norway, and bordered to the south by Germany. Denmark...
in 2004, Krogh's principle was cited as a central principle by the group at their 7th Congress. Krogh's principle has also been receiving attention in the area of functional genomics
Functional genomics
Functional genomics is a field of molecular biology that attempts to make use of the vast wealth of data produced by genomic projects to describe gene functions and interactions...
, where there has been increasing pressure and desire to expand genomics research to a more wide variety of organisms beyond the traditional scope of the field.
Philosophy and applications
A central concept to Krogh's principle is evolutionary adaptation. Evolutionary theory maintains that organisms are suited to particular nichesEcological niche
In ecology, a niche is a term describing the relational position of a species or population in its ecosystem to each other; e.g. a dolphin could potentially be in another ecological niche from one that travels in a different pod if the members of these pods utilize significantly different food...
, some of which are highly specialized for solving particular biological problems. These adaptations are typically exploited by biologists in several ways:
- Methodology: (i.e. Taq polymeraseTaq polymerasethumb|228px|right|Structure of Taq DNA polymerase bound to a DNA octamerTaq polymerase is a thermostable DNA polymerase named after the thermophilic bacterium Thermus aquaticus from which it was originally isolated by Thomas D. Brock in 1965...
and PCR): The need to manipulate biological systems in the laboratory has driven the use of an organismal specialization. One example of Krogh's principle presents itself in the heavily used Polymerase Chain ReactionPolymerase chain reactionThe polymerase chain reaction is a scientific technique in molecular biology to amplify a single or a few copies of a piece of DNA across several orders of magnitude, generating thousands to millions of copies of a particular DNA sequence....
(PCR), a method which relies on the rapid exposure of DNADNADeoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
to high heat for amplification of particular sequences of interest. DNA polymeraseDNA polymeraseA DNA polymerase is an enzyme that helps catalyze in the polymerization of deoxyribonucleotides into a DNA strand. DNA polymerases are best known for their feedback role in DNA replication, in which the polymerase "reads" an intact DNA strand as a template and uses it to synthesize the new strand....
enzymeEnzymeEnzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
from many organisms would denature at high temperatures, however, to solve this problem, Chien and colleagues turned to Thermus aquaticusThermus aquaticusThermus aquaticus is a species of bacterium that can tolerate high temperatures, one of several thermophilic bacteria that belong to the Deinococcus-Thermus group...
, a strain of bacteria native to hydrothermal ventHydrothermal ventA hydrothermal vent is a fissure in a planet's surface from which geothermally heated water issues. Hydrothermal vents are commonly found near volcanically active places, areas where tectonic plates are moving apart, ocean basins, and hotspots. Hydrothermal vents exist because the earth is both...
s. Thermus aquaticus has a polymerase that is heat stable at temperatures necessary for PCR. Biochemically modified Taq polymerase, as it is usually called, is now routinely used in PCR applications.
- Overcoming technical limitations: (i.e. large neuronNeuronA neuron is an electrically excitable cell that processes and transmits information by electrical and chemical signaling. Chemical signaling occurs via synapses, specialized connections with other cells. Neurons connect to each other to form networks. Neurons are the core components of the nervous...
s in MolluscaMolluscaThe Mollusca , common name molluscs or mollusksSpelled mollusks in the USA, see reasons given in Rosenberg's ; for the spelling mollusc see the reasons given by , is a large phylum of invertebrate animals. There are around 85,000 recognized extant species of molluscs. Mollusca is the largest...
): Two Nobel Prize winning bodies of study were facilitated by using ideas central to Krogh's principle to overcome technical limitations in nervous systemNervous systemThe nervous system is an organ system containing a network of specialized cells called neurons that coordinate the actions of an animal and transmit signals between different parts of its body. In most animals the nervous system consists of two parts, central and peripheral. The central nervous...
physiology. The ionic basisIon channelIon channels are pore-forming proteins that help establish and control the small voltage gradient across the plasma membrane of cells by allowing the flow of ions down their electrochemical gradient. They are present in the membranes that surround all biological cells...
of the action potentialAction potentialIn physiology, an action potential is a short-lasting event in which the electrical membrane potential of a cell rapidly rises and falls, following a consistent trajectory. Action potentials occur in several types of animal cells, called excitable cells, which include neurons, muscle cells, and...
was elucidated in the squid giant axonSquid giant axonThe squid giant axon is the very large axon that controls part of the water jet propulsion system in squid. It was discovered by English zoologist and neurophysiologist John Zachary Young in 1936...
, discovered by John Zachary YoungJohn Zachary YoungJohn Zachary Young FRS , generally known as "JZ" or "JZY", was an English zoologist and neurophysiologist, described as "one of the most influential biologists of the 20th century .....
. In 1958 HodgkinAlan Lloyd HodgkinSir Alan Lloyd Hodgkin, OM, KBE, PRS was a British physiologist and biophysicist, who shared the 1963 Nobel Prize in Physiology or Medicine with Andrew Huxley and John Eccles....
and HuxleyAndrew HuxleySir Andrew Fielding Huxley, OM, FRS is an English physiologist and biophysicist, who won the 1963 Nobel Prize in Physiology or Medicine for his experimental and mathematical work with Sir Alan Lloyd Hodgkin on the basis of nerve action potentials, the electrical impulses that enable the activity...
, developers of the original voltage clampVoltage clampThe voltage clamp is used by electrophysiologists to measure the ion currents across the membrane of excitable cells, such as neurons, while holding the membrane voltage at a set level. Cell membranes of excitable cells contain many different kinds of ion channels, some of which are voltage gated...
device and co-recipients of the 1963 Nobel Prize in Physiology or MedicineNobel Prize in Physiology or MedicineThe Nobel Prize in Physiology or Medicine administered by the Nobel Foundation, is awarded once a year for outstanding discoveries in the field of life science and medicine. It is one of five Nobel Prizes established in 1895 by Swedish chemist Alfred Nobel, the inventor of dynamite, in his will...
. The voltage clamp is now a central piece of technology in modern neurophysiologyNeurophysiologyNeurophysiology is a part of physiology. Neurophysiology is the study of nervous system function...
, but was only possible to develop using the wide diameter of the squid giant axon. Another marine mollusc, the opisthobranch AplysiaAplysiaAplysia is a genus of medium-sized to extremely large sea slugs, specifically sea hares, which are one clade of large sea slugs, marine gastropod mollusks. The general description of sea hares can be found in the article on the superfamily Aplysioidea....
possesses relatively small number of large nerve cells that are easily identified and mapped from individual to individual. Aplysia was selected for these reasons for the study of the cellular and molecular basis of learning and memory which led to Eric Kandel's receipt of the Nobel Prize in 2000.
- Understanding more complex/subtle systems (i.e. Barn owls and sound localizationSound localizationSound localization refers to a listener's ability to identify the location or origin of a detected sound in direction and distance. It may also refer to the methods in acoustical engineering to simulate the placement of an auditory cue in a virtual 3D space .The sound localization mechanisms of the...
): Beyond overcoming technical limitations, Krogh's principle has particularly important implications in the light of convergent evolutionConvergent evolutionConvergent evolution describes the acquisition of the same biological trait in unrelated lineages.The wing is a classic example of convergent evolution in action. Although their last common ancestor did not have wings, both birds and bats do, and are capable of powered flight. The wings are...
and homologyHomology (biology)Homology forms the basis of organization for comparative biology. In 1843, Richard Owen defined homology as "the same organ in different animals under every variety of form and function". Organs as different as a bat's wing, a seal's flipper, a cat's paw and a human hand have a common underlying...
. Either because of evolutionary history, or particular constraints on a given niche, there are not infinite solutions to all biological problems. Instead, organisms utilize similar neural algorithms, behaviors, or even structures to accomplish similar tasks. If one's goal is to understand how the nervous system might localize objects using sound, one may take the approach of using an auditoryAuditory systemThe auditory system is the sensory system for the sense of hearing.- Outer ear :The folds of cartilage surrounding the ear canal are called the pinna...
'specialist' such as the barn owl studied by Mark KonishiMasakazu Konishiis a Japanese neurobiologist, known for his research on prey capture auditory systems of barn owls and singing in songbirds.-Life:After growing up in wartime Kyoto, Konishi moved to study at Sapporo Agricultural College, Hokkaido University. Konishi studied for his doctoral thesis on properties of...
, Eric KnudsenEric KnudsenEric Knudsen is a professor of neurobiology at Stanford University. He is best known for his discovery, along with Masakazu Konishi, of a brain map of sound location in two dimensions in the barn owl, tyto alba...
and their colleagues. A nocturnal predator by nature, the barn owl relies heavily on using precise information on the time of arrival of sound in its ears. The information gleaned from this approach has contributed heavily to our understanding of how the brain maps sensory space, and how nervous systems encode timing information.
See also
- August KroghAugust KroghSchack August Steenberg Krogh FRS was a Danish professor of Romani background at the department of zoophysiology at the University of Copenhagen from 1916-1945...
- Comparative physiologyComparative physiologyComparative physiology is a subdiscipline of physiology that studies and exploits the diversity of functional characteristics of various kinds of organisms. It is closely related to evolutionary physiology and environmental physiology. Many universities offer undergraduate courses that cover...
- 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...
- NeuroethologyNeuroethologyNeuroethology is the evolutionary and comparative approach to the study of animal behavior and its underlying mechanistic control by the nervous system...
Further reading
- Bennett AF (2003). Experimental evolution and the Krogh Principle: generating biological novelty for functional and genetic analyses. Physiological and Biochemical Zoology 76:1-11. PDF
- Burggren WW (1999/2000). Developmental physiology, animal models, and the August Krogh principle. Zoology 102:148-156.
- Chien A, Edgar DB, Trela JM (1976). "Deoxyribonucleic acid polymerase from the extreme thermophile Thermus aquaticus". J. Bacteriol 174: 1550-1557
- Crawford, DL (2001). "Functional genomics does not have to be limited to a few select organisms". Genome Biology 2(1):interactions1001.1-1001.2.
- Krebs HA (1975). The August Krogh principle: "For many problems there is an animal on which it can be most conveniently studied." Journal of Experimental Zoology 194:221-226.
- Krogh A (1929). The progress of physiology. American Journal of Physiology 90:243-251.
- "Krogh's principle for a new era." (2003) [Editorial] Nature Genetics 34(4) pp. 345-346.
- Miller G. (2004) Behavioral Neuroscience Uncaged. Science 306(5695):432-434.