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Recurrent evolution also referred to as repeated or replicated evolution is the repeated
evolution Evolution is the change in the heritable Phenotypic trait, characteristics of biological populations over successive generations. It occurs when evolutionary processes such as natural selection and genetic drift act on genetic variation, re ...
of a particular trait, character, or
mutation In biology, a mutation is an alteration in the nucleic acid sequence of the genome of an organism, virus, or extrachromosomal DNA. Viral genomes contain either DNA or RNA. Mutations result from errors during DNA or viral replication, ...
. Most evolution is the result of drift, often interpreted as the random chance of some
allele An allele is a variant of the sequence of nucleotides at a particular location, or Locus (genetics), locus, on a DNA molecule. Alleles can differ at a single position through Single-nucleotide polymorphism, single nucleotide polymorphisms (SNP), ...
s being passed down to the next generation and others not. Recurrent evolution is said to occur when patterns emerge from this stochastic process when looking across multiple distinct populations. These patterns are of particular interest to evolutionary biologists, as they can demonstrate the underlying forces governing evolution. Recurrent evolution is a broad term, but it is usually used to describe recurring regimes of
selection Selection may refer to: Science * Selection (biology), also called natural selection, selection in evolution ** Sex selection, in genetics ** Mate selection, in mating ** Sexual selection in humans, in human sexuality ** Human mating strat ...
within or across lineages. While most commonly used to describe recurring patterns of selection, it can also be used to describe recurring patterns of
mutation In biology, a mutation is an alteration in the nucleic acid sequence of the genome of an organism, virus, or extrachromosomal DNA. Viral genomes contain either DNA or RNA. Mutations result from errors during DNA or viral replication, ...
; for example, transitions are more common than transversions. The concept encompasses both
convergent evolution Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last comm ...
and parallel evolution; it can be used to describe the observation of similar repeating changes through directional selection as well as the observation of highly conserved phenotypes or genotypes across lineages through continuous purifying selection over large periods of evolutionary time.


Phenotypic vs. genotypic levels

Recurrent changes may be observed at the
phenotype In genetics, the phenotype () is the set of observable characteristics or traits of an organism. The term covers the organism's morphology (physical form and structure), its developmental processes, its biochemical and physiological propert ...
level or the
genotype The genotype of an organism is its complete set of genetic material. Genotype can also be used to refer to the alleles or variants an individual carries in a particular gene or genetic location. The number of alleles an individual can have in a ...
level. At the phenotype level, recurrent evolution can be observed across a continuum of levels, which for simplicity can be broken down into molecular phenotype, cellular phenotype, and organismal phenotype. At the genotype level, recurrent evolution can only be detected using
DNA sequencing DNA sequencing is the process of determining the nucleic acid sequence – the order of nucleotides in DNA. It includes any method or technology that is used to determine the order of the four bases: adenine, thymine, cytosine, and guanine. The ...
data. The same or similar sequences appearing in the
genome 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 genes, other functional regions of the genome such as ...
s of different lineages indicates recurrent genomic evolution may have taken place. Recurrent genomic evolution can also occur within a lineage; an example of this would include some types of phase variation that involve highly directed changes at the DNA sequence level. The evolution of different forms of phase variation in separate lineages represents convergent and recurrent evolution toward increased evolvability. In organisms with long generation times, any potential recurrent genomic evolution within a lineage would be difficult to detect. Recurrent evolution has been studied most extensively at the organismal level, but with the advent of cheaper and faster sequencing technologies more attention is being paid to recurrent evolution at the genomic level.


Convergent, parallel, and recurrent evolution

The distinction between convergent and parallel evolution is somewhat unresolved in evolutionary biology. Some authors have claimed it is a
false dichotomy A false dilemma, also referred to as false dichotomy or false binary, is an informal fallacy based on a premise that erroneously limits what options are available. The source of the fallacy lies not in an invalid form of inference but in a false ...
, while others have argued that there are important distinctions. These debates are important when considering recurrent evolution because the basis for the distinction is in the degree of
phylogenetic In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical dat ...
relatedness among the organisms being considered. While convergent and parallel evolution can both be interpreted as forms of recurrent evolution, they involve multiple lineages whereas recurrent evolution can also take place within a single lineage. As mentioned before, recurrent evolution within a lineage can be difficult to detect in organisms with long generation times; however, paleontological evidence can be used to show recurrent phenotypic evolution within a lineage. The distinction between recurrent evolution across lineages and recurrent evolution within a lineage can be blurred because lineages do not have a set size and convergent or parallel evolution takes place among lineages that are all part of or within the same greater lineage. When speaking of recurrent evolution within a lineage, the simplest example is that given above, of the "on-off switch" used by bacteria in phase variation, but it can also involve phenotypic swings back and forth over longer periods of evolutionary history. These may be caused by environmental swings – for example, natural fluctuations in the climate, or a
pathogenic bacterium Pathogenic bacteria are bacteria that can cause disease. This article focuses on the bacteria that are pathogenic to humans. Most species of bacteria are harmless and many are beneficial but others can cause infectious diseases. The number of t ...
moving between hosts – and represent the other major source of recurrent evolution. Recurrent evolution caused by convergent and parallel evolution, and recurrent evolution caused by environmental swings, are not necessarily mutually exclusive. If the environmental swings have the same effect on the phenotypes of different species, they could potentially evolve in parallel back and forth together through each swing.


Examples


At the phenotypic level

On the island of
Bermuda Bermuda is a British Overseas Territories, British Overseas Territory in the Atlantic Ocean, North Atlantic Ocean. The closest land outside the territory is in the American state of North Carolina, about to the west-northwest. Bermuda is an ...
, the shell size of the land snail Poecilozonites has increased during glacial periods and shrunk again during warmer periods. It has been proposed that this is due to the increased size of the island during glacial periods (as a consequence of lower sea levels), which results in more large vertebrate predators and creates a selection pressure for larger shell size in the snails. In
eusocial Eusociality ( Greek 'good' and social) is the highest level of organization of sociality. It is defined by the following characteristics: cooperative brood care (including care of offspring from other individuals), overlapping generations wit ...
insects, new colonies are usually formed by a solitary queen, though this is not always the case. Dependent colony formation, when new colonies are formed by more than one individual, has evolved recurrently multiple times in ants, bees, and wasps. Recurrent evolution of polymorphisms in colonial invertebrate bryozoans of the order Cheilostomatida has given rise to zooid polymorphs and certain skeletal structures several times in evolutionary history. Neotropical tanagers of the genera '' Diglossa'' and '' Diglossopis'', known as flowerpiercers, have undergone recurrent evolution of divergent bill types. There is evidence for at least 133 transitions between
dioecy Dioecy ( ; ; adj. dioecious, ) is a characteristic of certain species that have distinct unisexual individuals, each producing either male or female gametes, either directly (in animals) or indirectly (in seed plants). Dioecious reproduction is ...
and hermaphroditism in the sexual systems of
bryophytes Bryophytes () are a group of land plants ( embryophytes), sometimes treated as a taxonomic division referred to as Bryophyta '' sensu lato'', that contains three groups of non-vascular land plants: the liverworts, hornworts, and mosses. In t ...
. Additionally, the transition rate from hermaphroditism to dioecy was approximately twice the rate in the reverse direction, suggesting greater diversification among hermaphrodites and demonstrating the recurrent evolution of dioecy in mosses. C4 photosynthesis has evolved over 60 times in different plant lineages. This has occurred through the repurposing of genes present in a C3 photosynthetic common ancestor, altering levels and patterns of
gene expression Gene expression is the process (including its Regulation of gene expression, regulation) by which information from a gene is used in the synthesis of a functional gene product that enables it to produce end products, proteins or non-coding RNA, ...
, and adaptive changes in the protein-coding region. Recurrent lateral gene transfer has also played a role in optimizing the C4 pathway by providing better adapted C4 genes to the plants.


At the genotypic level

Certain genetic mutations occur with measurable and consistent frequency. Deleterious and neutral alleles can increase in
frequency Frequency is the number of occurrences of a repeating event per unit of time. Frequency is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena, such as mechanical vibrations, audio ...
if the mutation rate to this phenotype is sufficiently higher than the reverse mutation rate; however, this appears to be rare. Beyond creating new
genetic variation Genetic variation is the difference in DNA among individuals or the differences between populations among the same species. The multiple sources of genetic variation include mutation and genetic recombination. Mutations are the ultimate sources ...
for selection to act upon, mutations plays a primary role in evolution when mutations in one direction are "weeded out by natural selection" and mutations in the other direction are neutral. This is known as purifying selection when it acts to maintain functionally important characters but also results in the loss or diminished size of useless organs as the functional constraint is lifted. An example of this is the diminished size of the
Y chromosome The Y chromosome is one of two sex chromosomes in therian mammals and other organisms. Along with the X chromosome, it is part of the XY sex-determination system, in which the Y is the sex-determining chromosome because the presence of the ...
in mammals, which can be attributed to recurrent mutations and recurrent evolution. The existence of mutational "hotspots" within the genome often gives rise to recurrent evolution. Hotspots can arise at certain nucleotide sequences because of interactions between the DNA and
DNA repair DNA repair is a collection of processes by which a cell (biology), cell identifies and corrects damage to the DNA molecules that encode its genome. A weakened capacity for DNA repair is a risk factor for the development of cancer. DNA is cons ...
, replication, and modification enzymes. These sequences can act like fingerprints to help researchers locate mutational hotspots. Cis-regulatory elements are frequent targets of evolution resulting in varied morphology. When looking at long-term evolution, mutations in cis-regulatory regions appear to be even more common. In other words, more interspecific morphological differences are caused by mutations in cis-regulatory regions than intraspecific differences. Across ''
Drosophila ''Drosophila'' (), from Ancient Greek δρόσος (''drósos''), meaning "dew", and φίλος (''phílos''), meaning "loving", is a genus of fly, belonging to the family Drosophilidae, whose members are often called "small fruit flies" or p ...
'' species, highly conserved blocks not only in the
histone In biology, histones are highly basic proteins abundant in lysine and arginine residues that are found in eukaryotic cell nuclei and in most Archaeal phyla. They act as spools around which DNA winds to create structural units called nucleosomes ...
fold domain but also in the N-terminal tail of centromeric
histone H3 Histone H3 is one of the five main histones involved in the structure of chromatin in eukaryotic cells. Featuring a main globular domain and a long N-terminal end, N-terminal tail, H3 is involved with the structure of the nucleosomes of the 'b ...
(CenH3) demonstrate recurrent evolution by purifying selection. In fact very similar oligopeptides in the N-terminal tails of CenH3 have also been observed in humans and in mice. Many divergent
eukaryotic The eukaryotes ( ) constitute the Domain (biology), domain of Eukaryota or Eukarya, organisms whose Cell (biology), cells have a membrane-bound cell nucleus, nucleus. All animals, plants, Fungus, fungi, seaweeds, and many unicellular organisms ...
lineages have recurrently evolved highly AT-rich genomes. GC-rich genomes are rarer among eukaryotes, but when they evolve independently in two different species the recurrent evolution of similar preferential codon usages will usually result. "Generally, regulatory genes occupying nodal position in
gene regulatory network A gene (or genetic) regulatory network (GRN) is a collection of molecular regulators that interact with each other and with other substances in the cell to govern the gene expression levels of mRNA and proteins which, in turn, determine the fu ...
s, and which function as morphogenetic switches, can be anticipated to be prime targets for evolutionary changes and therefore repeated evolution."


See also

*
Convergent evolution Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last comm ...
* Parallel evolution


References

{{reflist, colwidth=30em Evolutionary biology