Recurrent evolution is the repeated evolution of a particular trait, character, or mutation. Most evolution is the result of drift, often interpreted as the random chance of some alleles 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 within or across lineages. [1] While most commonly used to describe recurring patterns of selection, it can also be used to describe recurring patterns of mutation; for example, transitions are more common than transversions. [1] The concept encompasses both convergent evolution 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. [1]
Recurrent changes may be observed at the phenotype level or the genotype 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 data. The same or similar sequences appearing in the genomes 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.
The distinction between convergent and parallel evolution is somewhat unresolved in evolutionary biology. Some authors have claimed it is a false dichotomy, while others have argued that there are important distinctions. [2] [3] [4] [5] These debates are important when considering recurrent evolution because the basis for the distinction is in the degree of phylogenetic 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. [1] [6]
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. [6] 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. [6] These may be caused by environmental swings – for example, natural fluctuations in the climate, or a pathogenic bacterium moving between hosts – and represent the other major source of recurrent evolution. [6] 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.
On the island of Bermuda, 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. [6]
In eusocial 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. [7]
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. [8]
Neotropical tanagers of the genera Diglossa and Diglossopis , known as flowerpiercers, have undergone recurrent evolution of divergent bill types. [9]
There is evidence for at least 133 transitions between dioecy and hermaphroditism in the sexual systems of bryophytes. 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. [10]
C4 photosynthesis has evolved over 60 times in different plant lineages. [11] This has occurred through the repurposing of genes present in a C3 photosynthetic common ancestor, altering levels and patterns of gene expression, and adaptive changes in the protein-coding region. [11] Recurrent lateral gene transfer has also played a role in optimizing the C4 pathway by providing better adapted C4 genes to the plants. [11]
Certain genetic mutations occur with measurable and consistent frequency. [12] Deleterious and neutral alleles can increase in frequency 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 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. [12] 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 in mammals, which can be attributed to recurrent mutations and recurrent evolution. [12]
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, replication, and modification enzymes. [13] These sequences can act like fingerprints to help researchers locate mutational hotspots. [13]
Cis-regulatory elements are frequent targets of evolution resulting in varied morphology. [14] When looking at long-term evolution, mutations in cis-regulatory regions appear to be even more common. [15] In other words, more interspecific morphological differences are caused by mutations in cis-regulatory regions than intraspecific differences. [14]
Across Drosophila species, highly conserved blocks not only in the histone fold domain but also in the N-terminal tail of centromeric histone H3 (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. [16]
Many divergent eukaryotic lineages have recurrently evolved highly AT-rich genomes. [1] 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. [1]
"Generally, regulatory genes occupying nodal position in gene regulatory networks, and which function as morphogenetic switches, can be anticipated to be prime targets for evolutionary changes and therefore repeated evolution." [17]
Heredity, also called inheritance or biological inheritance, is the passing on of traits from parents to their offspring; either through asexual reproduction or sexual reproduction, the offspring cells or organisms acquire the genetic information of their parents. Through heredity, variations between individuals can accumulate and cause species to evolve by natural selection. The study of heredity in biology is genetics.
Microevolution is the change in allele frequencies that occurs over time within a population. This change is due to four different processes: mutation, selection, gene flow and genetic drift. This change happens over a relatively short amount of time compared to the changes termed macroevolution.
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, mitosis, or meiosis or other types of damage to DNA, which then may undergo error-prone repair, cause an error during other forms of repair, or cause an error during replication. Mutations may also result from insertion or deletion of segments of DNA due to mobile genetic elements.
In genetics, the phenotype is the set of observable characteristics or traits of an organism. The term covers the organism's morphology, its developmental processes, its biochemical and physiological properties, its behavior, and the products of behavior. An organism's phenotype results from two basic factors: the expression of an organism's genetic code and the influence of environmental factors. Both factors may interact, further affecting the phenotype. When two or more clearly different phenotypes exist in the same population of a species, the species is called polymorphic. A well-documented example of polymorphism is Labrador Retriever coloring; while the coat color depends on many genes, it is clearly seen in the environment as yellow, black, and brown. Richard Dawkins in 1978 and then again in his 1982 book The Extended Phenotype suggested that one can regard bird nests and other built structures such as caddisfly larva cases and beaver dams as "extended phenotypes".
Junk DNA is a DNA sequence that has no relevant biological function. Most organisms have some junk DNA in their genomes - mostly pseudogenes and fragments of transposons and viruses - but it is possible that some organisms have substantial amounts of junk DNA.
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 common ancestor of those groups. The cladistic term for the same phenomenon is homoplasy. The recurrent evolution of flight is a classic example, as flying insects, birds, pterosaurs, and bats have independently evolved the useful capacity of flight. Functionally similar features that have arisen through convergent evolution are analogous, whereas homologous structures or traits have a common origin but can have dissimilar functions. Bird, bat, and pterosaur wings are analogous structures, but their forelimbs are homologous, sharing an ancestral state despite serving different functions.
Molecular evolution is the process of change in the sequence composition of cellular molecules such as DNA, RNA, and proteins across generations. The field of molecular evolution uses principles of evolutionary biology and population genetics to explain patterns in these changes. Major topics in molecular evolution concern the rates and impacts of single nucleotide changes, neutral evolution vs. natural selection, origins of new genes, the genetic nature of complex traits, the genetic basis of speciation, the evolution of development, and ways that evolutionary forces influence genomic and phenotypic changes.
The neutral theory of molecular evolution holds that most evolutionary changes occur at the molecular level, and most of the variation within and between species are due to random genetic drift of mutant alleles that are selectively neutral. The theory applies only for evolution at the molecular level, and is compatible with phenotypic evolution being shaped by natural selection as postulated by Charles Darwin.
Population genetics is a subfield of genetics that deals with genetic differences within and among populations, and is a part of evolutionary biology. Studies in this branch of biology examine such phenomena as adaptation, speciation, and population structure.
In evolutionary genetics, Muller's ratchet is a process which, in the absence of recombination, results in an accumulation of irreversible deleterious mutations. This happens because in the absence of recombination, and assuming reverse mutations are rare, offspring bear at least as much mutational load as their parents. Muller proposed this mechanism as one reason why sexual reproduction may be favored over asexual reproduction, as sexual organisms benefit from recombination and consequent elimination of deleterious mutations. The negative effect of accumulating irreversible deleterious mutations may not be prevalent in organisms which, while they reproduce asexually, also undergo other forms of recombination. This effect has also been observed in those regions of the genomes of sexual organisms that do not undergo recombination.
Evolutionary biology is the subfield of biology that studies the evolutionary processes that produced the diversity of life on Earth. It is also defined as the study of the history of life forms on Earth. Evolution holds that all species are related and gradually change over generations. In a population, the genetic variations affect the phenotypes of an organism. These changes in the phenotypes will be an advantage to some organisms, which will then be passed onto their offspring. Some examples of evolution in species over many generations are the peppered moth and flightless birds. In the 1930s, the discipline of evolutionary biology emerged through what Julian Huxley called the modern synthesis of understanding, from previously unrelated fields of biological research, such as genetics and ecology, systematics, and paleontology.
Gene duplication is a major mechanism through which new genetic material is generated during molecular evolution. It can be defined as any duplication of a region of DNA that contains a gene. Gene duplications can arise as products of several types of errors in DNA replication and repair machinery as well as through fortuitous capture by selfish genetic elements. Common sources of gene duplications include ectopic recombination, retrotransposition event, aneuploidy, polyploidy, and replication slippage.
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.
Comparative genomics is a field of biological research in which the genomic features of different organisms are compared. The genomic features may include the DNA sequence, genes, gene order, regulatory sequences, and other genomic structural landmarks. In this branch of genomics, whole or large parts of genomes resulting from genome projects are compared to study basic biological similarities and differences as well as evolutionary relationships between organisms. The major principle of comparative genomics is that common features of two organisms will often be encoded within the DNA that is evolutionarily conserved between them. Therefore, comparative genomic approaches start with making some form of alignment of genome sequences and looking for orthologous sequences in the aligned genomes and checking to what extent those sequences are conserved. Based on these, genome and molecular evolution are inferred and this may in turn be put in the context of, for example, phenotypic evolution or population genetics.
Evidence of common descent of living organisms has been discovered by scientists researching in a variety of disciplines over many decades, demonstrating that all life on Earth comes from a single ancestor. This forms an important part of the evidence on which evolutionary theory rests, demonstrates that evolution does occur, and illustrates the processes that created Earth's biodiversity. It supports the modern evolutionary synthesis—the current scientific theory that explains how and why life changes over time. Evolutionary biologists document evidence of common descent, all the way back to the last universal common ancestor, by developing testable predictions, testing hypotheses, and constructing theories that illustrate and describe its causes.
The evolution of biological complexity is one important outcome of the process of evolution. Evolution has produced some remarkably complex organisms – although the actual level of complexity is very hard to define or measure accurately in biology, with properties such as gene content, the number of cell types or morphology all proposed as possible metrics.
The following outline is provided as an overview of and topical guide to genetics:
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. Overlapping and related terms can be found in Glossary of cellular and molecular biology, Glossary of ecology, and Glossary of biology.
In evolutionary biology, developmental bias refers to the production against or towards certain ontogenetic trajectories which ultimately influence the direction and outcome of evolutionary change by affecting the rates, magnitudes, directions and limits of trait evolution. Historically, the term was synonymous with developmental constraint, however, the latter has been more recently interpreted as referring solely to the negative role of development in evolution.
Henry HQ Heng is a professor of molecular medicine and genetics and of pathology at the Wayne State University School of Medicine. Heng first received his PhD from the University of Toronto Hospital for Sick Children in 1994, mentored by Lap-Chee Tsui. He then completed his post-doc under Peter Moens at York University, before joining the Wayne State University School of Medicine faculty.
