In biology, 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 together in response to the same selective pressure 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. [1]
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. [2] [1]
Proteins often act in complex interactions with other proteins and functionally related proteins often show a similar evolutionary path. [1] [3] A possible explanation is co-adaptation. [1] An example of this is the interaction between proteins encoded by mitochondrial DNA (mtDNA) and nuclear DNA (nDNA). MtDNA has a higher rate of evolution/mutation than nDNA, especially in specific coding regions. [2] [3] However, in order to maintain physiological functionality, selection for functionally interacting proteins, and therefore co-adapted nDNA will be favourable. [2]
Co-adaptation between mtDNA and nDNA sequences has been studied in the copepod Tigriopus californicus . [2] The mtDNA of COII coding sequences among conspecific populations of this species diverges extensively. [2] When mtDNA of one population was placed in a nuclear background of another population, cytochrome c oxidase 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). [2]
Gene blocks in bacterial genomes are sequences of genes, co-located on the chromosome, that are evolutionarily conserved across numerous taxa. [4] Some conserved blocks are operons, where the genes are cotranscribed to polycistronic mRNA, and such operons are often associated with a single function such as a metabolic pathway or a protein complex. [4] The co-location of genes with related function and the preservation of these relationships over evolutionary time indicates that natural selection has been operating to maintain a co-adaptive benefit.
As the early mapping of genes on the bacteriophage T4 chromosome progressed, it became evident that the arrangement of the genes is far from random. [5] 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 are tightly clustered. [6] Other examples of apparently co-adapted clusters are the genes that determine the baseplate wedge, the tail fibers, and DNA polymerase accessory proteins. [6] 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 [7] 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.
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. [8]
Weakly electric fish are capable of creating a weak electric field using an electric organ. 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. Research on ghost knifefish [9] 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.
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. [10] Parent-offspring co-adaptation 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. [11]
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 skinks [12] 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 , the optimum temperature and preferred temperature diverged from one another in opposite directions, creating antagonistic co-adaptation.
A bacteriophage, also known informally as a phage, is a virus that infects and replicates within bacteria and archaea. The term was derived from "bacteria" and the Greek φαγεῖν, meaning "to devour". Bacteriophages are composed of proteins that encapsulate a DNA or RNA genome, and may have structures that are either simple or elaborate. Their genomes may encode as few as four genes and as many as hundreds of genes. Phages replicate within the bacterium following the injection of their genome into its cytoplasm.
DNA ligase is a type of enzyme that facilitates the joining of DNA strands together by catalyzing the formation of a phosphodiester bond. It plays a role in repairing single-strand breaks in duplex DNA in living organisms, but some forms may specifically repair double-strand breaks. Single-strand breaks are repaired by DNA ligase using the complementary strand of the double helix as a template, with DNA ligase creating the final phosphodiester bond to fully repair the DNA.
Genetic recombination is the exchange of genetic material between different organisms which leads to production of offspring with combinations of traits that differ from those found in either parent. In eukaryotes, genetic recombination during meiosis can lead to a novel set of genetic information that can be further passed on from parents to offspring. Most recombination occurs naturally and can be classified into two types: (1) interchromosomal recombination, occurring through independent assortment of alleles whose loci are on different but homologous chromosomes ; & (2) intrachromosomal recombination, occurring through crossing over.
Viral evolution is a subfield of evolutionary biology and virology that is specifically concerned with the evolution of viruses. Viruses have short generation times, and many—in particular RNA viruses—have relatively high mutation rates. Although most viral mutations confer no benefit and often even prove deleterious to viruses, the rapid rate of viral mutation combined with natural selection allows viruses to quickly adapt to changes in their host environment. In addition, because viruses typically produce many copies in an infected host, mutated genes can be passed on to many offspring quickly. Although the chance of mutations and evolution can change depending on the type of virus, viruses overall have high chances for mutations.
Evolvability is defined as the capacity of a system for adaptive evolution. Evolvability is the ability of a population of organisms to not merely generate genetic diversity, but to generate adaptive genetic diversity, and thereby evolve through natural selection.
Escherichia virus T4 is a species of bacteriophages that infect Escherichia coli bacteria. It is a double-stranded DNA virus in the subfamily Tevenvirinae of the family Straboviridae. T4 is capable of undergoing only a lytic life cycle and not the lysogenic life cycle. The species was formerly named T-even bacteriophage, a name which also encompasses, among other strains, Enterobacteria phage T2, Enterobacteria phage T4 and Enterobacteria phage T6.
Exaptation or co-option is a shift in the function of a trait during evolution. For example, a trait can evolve because it served one particular function, but subsequently it may come to serve another. Exaptations are common in both anatomy and behaviour.
Pleiotropy occurs when one gene influences two or more seemingly unrelated phenotypic traits. Such a gene that exhibits multiple phenotypic expression is called a pleiotropic gene. Mutation in a pleiotropic gene may have an effect on several traits simultaneously, due to the gene coding for a product used by a myriad of cells or different targets that have the same signaling function.
Complementation refers to a genetic process when two strains of an organism with different homozygous recessive mutations that produce the same mutant phenotype have offspring that express the wild-type phenotype when mated or crossed. Complementation will ordinarily occur if the mutations are in different genes. Complementation may also occur if the two mutations are at different sites within the same gene, but this effect is usually weaker than that of intergenic complementation. When the mutations are in different genes, each strain's genome supplies the wild-type allele to "complement" the mutated allele of the other strain's genome. Since the mutations are recessive, the offspring will display the wild-type phenotype. A complementation test can test whether the mutations in two strains are in different genes. Complementation is usually weaker or absent if the mutations are in the same gene. The convenience and essence of this test is that the mutations that produce a phenotype can be assigned to different genes without the exact knowledge of what the gene product is doing on a molecular level. American geneticist Edward B. Lewis developed the complementation test.
Directed evolution (DE) is a method used in protein engineering that mimics the process of natural selection to steer proteins or nucleic acids toward a user-defined goal. It consists of subjecting a gene to iterative rounds of mutagenesis, selection and amplification. It can be performed in vivo, or in vitro. Directed evolution is used both for protein engineering as an alternative to rationally designing modified proteins, as well as for experimental evolution studies of fundamental evolutionary principles in a controlled, laboratory environment.
Enquiry into the evolution of ageing, or aging, aims to explain why a detrimental process such as ageing would evolve, and why there is so much variability in the lifespans of organisms. The classical theories of evolution suggest that environmental factors, such as predation, accidents, disease, and/or starvation, ensure that most organisms living in natural settings will not live until old age, and so there will be very little pressure to conserve genetic changes that increase longevity. Natural selection will instead strongly favor genes which ensure early maturation and rapid reproduction, and the selection for genetic traits which promote molecular and cellular self-maintenance will decline with age for most organisms.
Sexual conflict or sexual antagonism occurs when the two sexes have conflicting optimal fitness strategies concerning reproduction, particularly over the mode and frequency of mating, potentially leading to an evolutionary arms race between males and females. In one example, males may benefit from multiple matings, while multiple matings may harm or endanger females due to the anatomical differences of that species. Sexual conflict underlies the evolutionary distinction between male and female.
Lethal alleles are alleles that cause the death of the organism that carries them. They are usually a result of mutations in genes that are essential for growth or development. Lethal alleles may be recessive, dominant, or conditional depending on the gene or genes involved.
Experimental evolution studies are a means of testing evolutionary theory under carefully designed, reproducible experiments. Given enough time, space, and money, any organism could be used for experimental evolution studies. However, those with rapid generation times, high mutation rates, large population sizes, and small sizes increase the feasibility of experimental studies in a laboratory context. For these reasons, bacteriophages are especially favored by experimental evolutionary biologists. Bacteriophages, and microbial organisms, can be frozen in stasis, facilitating comparison of evolved strains to ancestors. Additionally, microbes are especially labile from a molecular biologic perspective. Many molecular tools have been developed to manipulate the genetic material of microbial organisms, and because of their small genome sizes, sequencing the full genomes of evolved strains is trivial. Therefore, comparisons can be made for the exact molecular changes in evolved strains during adaptation to novel conditions.
Host–parasite coevolution is a special case of coevolution, where a host and a parasite continually adapt to each other. This can create an evolutionary arms race between them. A more benign possibility is of an evolutionary trade-off between transmission and virulence in the parasite, as if it kills its host too quickly, the parasite will not be able to reproduce either. Another theory, the Red Queen hypothesis, proposes that since both host and parasite have to keep on evolving to keep up with each other, and since sexual reproduction continually creates new combinations of genes, parasitism favours sexual reproduction in the host.
Epigenetics is the study of changes in gene expression that occur via mechanisms such as DNA methylation, histone acetylation, and microRNA modification. When these epigenetic changes are heritable, they can influence evolution. Current research indicates that epigenetics has influenced evolution in a number of organisms, including plants and animals.
Epistasis is a phenomenon in genetics in which the effect of a gene mutation is dependent on the presence or absence of mutations in one or more other genes, respectively termed modifier genes. In other words, the effect of the mutation is dependent on the genetic background in which it appears. Epistatic mutations therefore have different effects on their own than when they occur together. Originally, the term epistasis specifically meant that the effect of a gene variant is masked by that of different gene.
Endogenosymbiosis is an evolutionary process, proposed by the evolutionary and environmental biologist Roberto Cazzolla Gatti, in which "gene carriers" and symbiotic prokaryotic cells could share parts or all of their genomes in an endogenous symbiotic relationship with their hosts.
This glossary of genetics and evolutionary biology is a list of definitions of terms and concepts used in the study of genetics and evolutionary biology, as well as sub-disciplines and related fields, with an emphasis on classical genetics, quantitative genetics, population biology, phylogenetics, speciation, and systematics. It has been designed as a companion to Glossary of cellular and molecular biology, which contains many overlapping and related terms; other related glossaries include Glossary of biology and Glossary of ecology.
Constructive neutral evolution(CNE) is a theory that seeks to explain how complex systems can evolve through neutral transitions and spread through a population by chance fixation (genetic drift). Constructive neutral evolution is a competitor for both adaptationist explanations for the emergence of complex traits and hypotheses positing that a complex trait emerged as a response to a deleterious development in an organism. Constructive neutral evolution often leads to irreversible or "irremediable" complexity and produces systems which, instead of being finely adapted for performing a task, represent an excess complexity that has been described with terms such as "runaway bureaucracy" or even a "Rube Goldberg machine".
