Co-adaptation
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biology Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that tie it together as a single, coherent field. For instance, all organisms are made up of cells that process hereditary i ...
, co-adaptation is the process by which two or more species, genes or phenotypic traits undergo adaptation as a pair or group. This occurs when two or more interacting characteristics undergo
natural selection Natural selection is the differential survival and reproduction of individuals due to differences in phenotype. It is a key mechanism of evolution, the change in the heritable traits characteristic of a population over generations. Cha ...
together in response to the same
selective pressure Any cause that reduces or increases reproductive success in a portion of a population potentially exerts evolutionary pressure, selective pressure or selection pressure, driving natural selection. It is a quantitative description of the amount of ...
or when selective pressures alter one characteristic and consecutively alter the interactive characteristic. These interacting characteristics are only beneficial when together, sometimes leading to increased interdependence. Co-adaptation and coevolution, although similar in process, are not the same; co-adaptation refers to the interactions between two units, whereas co-evolution refers to their evolutionary history. Co-adaptation and its examples are often seen as evidence for co-evolution.


Genes and Protein Complexes

At genetic level, co-adaptation is the accumulation of interacting genes in the gene pool of a population by selection. Selection pressures on one of the genes will affect its interacting proteins, after which compensatory changes occur. Proteins often act in complex interactions with other proteins and functionally related proteins often show a similar evolutionary path. A possible explanation is co-adaptation. An example of this is the interaction between proteins encoded by mitochondrial DNA (mtDNA) and
nuclear DNA Nuclear DNA (nDNA), or nuclear deoxyribonucleic acid, is the DNA contained within each cell nucleus of a eukaryotic organism. It encodes for the majority of the genome in eukaryotes, with mitochondrial DNA and plastid DNA coding for the rest. I ...
(nDNA). MtDNA has a higher rate of evolution/mutation than nDNA, especially in specific coding regions. However, in order to maintain physiological functionality, selection for functionally interacting proteins, and therefore co-adapted nDNA will be favourable. Co-adaptation between mtDNA and nDNA sequences has been studied in the copepod '' Tigriopus californicus''. The mtDNA of COII coding sequences among conspecific populations of this species diverges extensively. When mtDNA of one population was placed in a nuclear background of another population,
cytochrome c oxidase The enzyme cytochrome c oxidase or Complex IV, (was , now reclassified as a translocasEC 7.1.1.9 is a large transmembrane protein complex found in bacteria, archaea, and mitochondria of eukaryotes. It is the last enzyme in the respiratory elect ...
activity is significantly decreased, suggesting co-adaptation. Results show an unlikely relationship between the variation in mtDNA and environmental factors. A more likely explanation is the neutral evolution of mtDNA with compensatory changes by the nDNA driven by neutral evolution of mtDNA (random mutations over time in isolated populations).


Bacteria and bacteriophage

Gene In biology, the word gene (from , ; "... Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a b ...
blocks in
bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few micrometr ...
l
genome In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding g ...
s are sequences of genes, co-located on the
chromosome A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins are ...
, that are evolutionarily conserved across numerous taxa.Ream DC, Bankapur AR, Friedberg I. An event-driven approach for studying gene block evolution in bacteria. Bioinformatics. 2015 Jul 1;31(13):2075-83. doi: 10.1093/bioinformatics/btv128. Epub 2015 Feb 25. PMID 25717195; PMCID: PMC4481853 Some conserved blocks are
operon In genetics, an operon is a functioning unit of DNA containing a cluster of genes under the control of a single promoter. The genes are transcribed together into an mRNA strand and either translated together in the cytoplasm, or undergo splic ...
s, where the genes are cotranscribed to polycistonic
mRNA In molecular biology, messenger ribonucleic acid (mRNA) is a single-stranded molecule of RNA that corresponds to the genetic sequence of a gene, and is read by a ribosome in the process of synthesizing a protein. mRNA is created during the ...
, and such operons are often associated with a single function such as a
metabolic pathway In biochemistry, a metabolic pathway is a linked series of chemical reactions occurring within a cell. The reactants, products, and intermediates of an enzymatic reaction are known as metabolites, which are modified by a sequence of chemical reac ...
or a
protein complex A protein complex or multiprotein complex is a group of two or more associated polypeptide chains. Protein complexes are distinct from multienzyme complexes, in which multiple catalytic domains are found in a single polypeptide chain. Protein ...
. The co-location of genes with related function and the preservation of these relationships over evolutionary time indicates that
natural selection Natural selection is the differential survival and reproduction of individuals due to differences in phenotype. It is a key mechanism of evolution, the change in the heritable traits characteristic of a population over generations. Cha ...
has been operating to maintain a co-adaptive benefit. As the early mapping of genes on the
bacteriophage T4 Escherichia virus T4 is a species of bacteriophages that infect ''Escherichia coli'' bacteria. It is a double-stranded DNA virus in the subfamily '' Tevenvirinae'' from the family Myoviridae. T4 is capable of undergoing only a lytic lifecycle ...
chromosome progressed, it became evident that the arrangement of the genes is far from random. Genes with like functions tend to fall into clusters and appear to be co-adapted to each other. For instance genes that specify proteins employed in bacteriophage head
morphogenesis Morphogenesis (from the Greek ''morphê'' shape and ''genesis'' creation, literally "the generation of form") is the biological process that causes a cell, tissue or organism to develop its shape. It is one of three fundamental aspects of deve ...
are tightly clustered.Kutter E, T Stidham, B Guttman, E Kutter, D Batts, S Peterson, T Djavakhishvili, F Arisaka, V Mesyanzhinov, W Ruger, G Mosig. 1994. Genomic map of bacteriophage T4, p. 491–519. In J Karam, JW Drake, KN Kreuzer, G Mosig, DH Hall, FA Eiserling, LW Black, EK Spicer, E Kutter, K Carlson, ES Miller (ed.), Molecular biology of bacteriophage T4. American Society for Microbiology, Washington, D.C. Other examples of apparently co-adapted clusters are the genes that determine the baseplate wedge, the tail fibers, and
DNA polymerase A DNA polymerase is a member of a family of enzymes that catalyze the synthesis of DNA molecules from nucleoside triphosphates, the molecular precursors of DNA. These enzymes are essential for DNA replication and usually work in groups to create ...
accessory proteins. In other cases where the structural relationship of the gene products is not as evident, a co-adapted clustering based on functional interaction may also occur. Thus Obringer proposed that a specific cluster of genes, centered around the ''imm'' and ''spackle'' genes encodes proteins adapted for competition and defense at the DNA level.


Organs

Similar to traits on a genetic level, aspects of organs can also be subject to co-adaptation. For example, slender bones can have similar performance in regards to bearing daily loads as thicker bones, due to slender bones having more mineralized tissue. This means that slenderness and the level of mineralization have probably been co-adapted. However, due to being harder than thick bones, slender bones are generally less pliant and more prone to breakage, especially when subjected to more extreme load conditions. Weakly electric fish are capable of creating a weak electric field using an
electric organ An electric organ, also known as electronic organ, is an electronic keyboard instrument which was derived from the pump organ, harmonium, pipe organ and theatre organ. Originally designed to imitate their sound, or orchestral sounds, it has sinc ...
. These electric fields can be used to communicate between individuals through electric organ discharges (EOD), which can be further modulated to create context-specific signals called ‘chirps’. Fish can sense these electric fields and signals using
electroreceptors Electroreception and electrogenesis are the closely-related biological abilities to perceive electrical stimuli and to generate electric fields. Both are used to locate prey; stronger electric discharges are used in a few groups of fishes to st ...
. Research on
ghost knifefish The ghost knifefishes are a family, Apteronotidae, of ray-finned fishes in the order Gymnotiformes. These fish are native to Panama and South America. They inhabit a wide range of freshwater habitats, but more than half the species in the family ...
indicates that the signals produced by electric fish and the way they are received might be co-adapted, as the environment in which the fish resides (both physical and social) influences selection for the chirps, EODs, and detection. Interactions between territorial fish favour different signal parameters than interactions within social groups of fish.


Behaviour

The behaviour of parents and their offspring during feeding is influenced by one another. Parents feed depending on how much their offspring begs, while the offspring begs depending on how hungry it is. This would normally lead to a conflict of interest between parent and offspring, as the offspring will want to be fed as much as possible, whereas the parent can only invest a limited amount of energy into parental care. As such, selection would occur for the combination of begging and feeding behaviours that leads to the highest fitness, resulting in co-adaptation. Parent-offspring co-adaption can be further influenced by information asymmetry, such as female blue tits being exposed more to begging behaviour in nature, resulting in them responding more than males to similar levels of stimuli.


Partial and antagonistic co-adaptation

It is also possible for related traits to only partially co-adapt due to traits not developing at the same speed, or contradict each other entirely. Research on Australian skinksHuey, R. B., and A. F. Bennett. 1987. Phylogenetic studies of coadaptation: preferred temperatures versus optimal performance temperatures of lizards. Evolution 41:1098–1115. revealed that diurnal skinks have a high temperature preference and can sprint optimally at higher temperatures, while nocturnal skinks have a low preferred temperature and optimum temperature. However, the differences between high and low optimal temperatures were much smaller than between preferred temperatures, which means that nocturnal skinks sprint slower compared to their diurnal counterparts. In the case of ''
Eremiascincus ''Eremiascincus'' is a genus of skinks, lizards in the family Scincidae. The genus is endemic to Australia, Indonesia, and East Timor. Species The genus contains the following 15 valid species, listed alphabetically by specific name.
'', the optimum temperature and preferred temperature diverged from one another in opposite directions, creating antagonistic co-adaptation.


See also

*
Evolutionary biology Evolutionary biology is the subfield of biology that studies the evolutionary processes ( natural selection, common descent, speciation) that produced the diversity of life on Earth. It is also defined as the study of the history of life ...
* Coevolution * Mutualism * Symbiosis *
Linkage disequilibrium In population genetics, linkage disequilibrium (LD) is the non-random association of alleles at different loci in a given population. Loci are said to be in linkage disequilibrium when the frequency of association of their different alleles is h ...
* Epistasis


References

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External links


Coadaptation entry
in a dictionary on
evolution Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...
. Evolutionary biology