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Sunday, March 20, 2022

Left-wing politics

From Wikipedia, the free encyclopedia

5 May 1789 opening of the Estates General of 1789 in Versailles
 
Labour union demonstrators at the 1912 Lawrence textile strike

Left-wing politics support social equality and egalitarianism, often in opposition of social hierarchy. Left-wing politics typically involve a concern for those in society whom its adherents perceive as disadvantaged relative to others as well as a belief that there are unjustified inequalities that need to be reduced or abolished. According to emeritus professor of economics Barry Clark, left-wing supporters "claim that human development flourishes when individuals engage in cooperative, mutually respectful relations that can thrive only when excessive differences in status, power, and wealth are eliminated."

Within the left–right political spectrum, Left and Right were coined during the French Revolution, referring to the seating arrangement in the French Estates General. Those who sat on the left generally opposed the Ancien Régime and the Bourbon monarchy and supported the French Revolution, the creation of a democratic republic and the secularisation of society while those on the right were supportive of the traditional institutions of the Old Regime. Usage of the term Left became more prominent after the restoration of the French monarchy in 1815, when it was applied to the Independents. The word wing was first appended to Left and Right in the late 19th century, usually with disparaging intent, and left-wing was applied to those who were unorthodox in their religious or political views.

The term Left was later applied to a number of movements, especially republicanism in France during the 18th century, followed by socialism, including anarchism, communism, the labour movement, Marxism, social democracy and syndicalism in the 19th and 20th centuries. Since then, the term left-wing has been applied to a broad range of movements, including the civil rights movement, feminist movement, LGBT rights movement, multiculturalism, anti-war movement and environmental movement as well as a wide range of political parties.

Positions

The following positions are typically associated with left-wing politics.

Economics

Leftist economic beliefs range from Keynesian economics and the welfare state through industrial democracy and the social market to the nationalization of the economy and central planning, to the anarcho-syndicalist advocacy of a council- and assembly-based self-managed anarchist communism. During the Industrial Revolution, leftists supported trade unions. At the beginning of the 20th century, many leftists advocated strong government intervention in the economy. Leftists continue to criticize the perceived exploitative nature of globalization, the "race to the bottom" and unjust lay-offs and exploitation of workers. In the last quarter of the 20th century, the belief that the government (ruling in accordance with the interests of the people) ought to be directly involved in the day-to-day workings of an economy declined in popularity amongst the centre-left, especially social democrats who adopted the Third Way.

Other leftists believe in Marxian economics, named after the economic theories of Karl Marx. Some distinguish Marx's economic theories from his political philosophy, arguing that Marx's approach to understanding the economy is independent of his advocacy of revolutionary socialism or his belief in the inevitability of a proletarian revolution. Marxian economics do not exclusively rely on Marx and draw from a range of Marxist and non-Marxist sources. The dictatorship of the proletariat and workers' state are terms used by some Marxists, particularly Leninists and Marxist–Leninists, to describe what they see as a temporary state between the capitalist state of affairs and a communist society. Marx defined the proletariat as salaried workers, in contrast to the lumpenproletariat, who he defined as the outcasts of society such as beggars, tricksters, entertainers, buskers, criminals and prostitutes. The political relevance of farmers has divided the left. In Das Kapital, Marx scarcely mentioned the subject. Mikhail Bakunin thought the lumpenproletariat was a revolutionary class while Mao Zedong believed that it would be rural peasants, not urban workers, who would bring about the proletarian revolution.

Left-libertarians, libertarian socialists and anarchists believe in a decentralized economy run by trade unions, workers' councils, cooperatives, municipalities and communes, opposing both state and private control of the economy, preferring social ownership and local control in which a nation of decentralized regions is united in a confederation. The global justice movement, also known as the anti-globalisation movement and the alter-globalisation movement, protests against corporate economic globalisation due to its negative consequences for the poor, workers, the environment, and small businesses.

Environment

One of the foremost left-wing advocates was Thomas Paine, one of the first individuals since left and right became political terms to describe the collective human ownership of the world which he speaks of in Agrarian Justice. As such, most of left-wing thought and literature regarding environmentalism stems from this duty of ownership and the aforementioned form of cooperative ownership means that humanity must take care of the Earth. This principle is reflected in much of the historical left-wing thought and literature that came afterwards, although there were disagreements about what this entailed. Both Karl Marx and the early socialist philosopher and scholar William Morris arguably had a concern for environmental matters. According to Marx, "[e]ven an entire society, a nation, or all simultaneously existing societies taken together, are not the owners of the earth. They are simply its possessors, its beneficiaries, and have to bequeath it in an improved state to succeeding generations". Following the Russian Revolution, environmental scientists such as revolutionary Alexander Bogdanov and the Proletkult organisation made efforts to incorporate environmentalism into Bolshevism and "integrate production with natural laws and limits" in the first decade of Soviet rule, before Joseph Stalin attacked ecologists and the science of ecology, purged environmentalists and promoted the pseudoscience of Trofim Lysenko during his rule up until his death in 1953. Similarly, Mao Zedong rejected environmentalism and believed that based on the laws of historical materialism, all of nature must be put into the service of revolution.

From the 1970s onwards, environmentalism became an increasing concern of the left, with social movements and several unions campaigning on environmental issues and causes. In Australia, the left-wing Builders Labourers Federation, led by the communist Jack Mundy, united with environmentalists to place green bans on environmentally destructive development projects. Several segments of the socialist and Marxist left consciously merged environmentalism and anti-capitalism into an eco-socialist ideology. Barry Commoner articulated a left-wing response to The Limits to Growth model that predicted catastrophic resource depletion and spurred environmentalism, postulating that capitalist technologies were the key cause responsible for environmental degradation, as opposed to human population pressures. Environmental degradation can be seen as a class or equity issue, as environmental destruction disproportionately affects poorer communities and countries.

Global warming was the cover story of this 2007 issue of the Ms. magazine.

Several left-wing or socialist groupings have an overt environmental concern and several green parties contain a strong socialist presence. The Green Party of England and Wales features an eco-socialist group, the Green Left, which was founded in June 2005. Its members held several influential positions within the party, including both the former Principal Speakers Siân Berry and Derek Wall, himself an eco-socialist and Marxist academic. In Europe, several green left political parties such as the European United Left–Nordic Green Left combine traditional social-democratic values such as a desire for greater economic equality and workers rights with demands for environmental protection. Democratic socialist Bolivian president Evo Morales has traced environmental degradation to capitalist consumerism, stating that "[t]he Earth does not have enough for the North to live better and better, but it does have enough for all of us to live well". James Hansen, Noam Chomsky, Raj Patel, Naomi Klein, The Yes Men and Dennis Kucinich hold similar views.

In the 21st century, questions about the environment have become increasingly politicized as the Left almost unanimously accepted the findings and consensus of environmental scientists and climatologists about anthropogenic global warming, while the Right has disputed or outright rejected the scientific consensus that modern-day global warming is caused by human activity. However, the Left is also divided over how to effectively and equitably reduce carbon emissions as the center-left often advocates a reliance on market measures such as emissions trading and a carbon tax while those further to the left support direct government regulation and intervention in the form of a Green New Deal, either alongside or instead of market mechanisms.

Nationalism, anti-imperialism and anti-nationalism

The question of nationality, imperialism and nationalism has been a central feature of political debates on the Left. During the French Revolution, nationalism was a key policy of the Republican Left. The Republican Left advocated for civic nationalism and argued that the nation is a "daily plebiscite" formed by the subjective "will to live together". Related to revanchism, the belligerent will to take revenge against Germany and retake control of Alsace-Lorraine, nationalism was sometimes opposed to imperialism. In the 1880s, there was a debate between leftists such as the Radical Georges Clemenceau, the Socialist Jean Jaurès and the nationalist Maurice Barrès, who argued that colonialism diverted France from liberating the "blue line of the Vosges", in reference to Alsace-Lorraine; and the "colonial lobby" such as Jules Ferry of the Moderate Republicans, Léon Gambetta of the Republicans and Eugène Etienne, the president of the Parliamentary Colonial Group. After the antisemitic Dreyfus Affair in which officer Alfred Dreyfus was falsely convicted of sedition and exiled to a penal colony in 1894 before being exonerated in 1906, nationalism in the form of Boulangism increasingly became associated with the far-right.

The Marxist social class theory of proletarian internationalism asserts that members of the working class should act in solidarity with working people in other countries in pursuit of a common class interest, rather than only focusing on their own countries. Proletarian internationalism is summed up in the slogan: "Workers of the world, unite!", the last line of The Communist Manifesto. Union members had learned that more members meant more bargaining power. Taken to an international level, leftists argued that workers should act in solidarity with the international proletariat in order to further increase the power of the working class. Proletarian internationalism saw itself as a deterrent against war and international conflicts, because people with a common interest are less likely to take up arms against one another, instead focusing on fighting the bourgeoisie as the ruling class. According to Marxist theory, the antonym of proletarian internationalism is bourgeois nationalism. Some Marxists, together with others on the left, view nationalism, racism (including antisemitism) and religion as divide and conquer tactics used by the ruling classes to prevent the working class from uniting against them in solidarity with one another. Left-wing movements have often taken up anti-imperialist positions. Anarchism has developed a critique of nationalism that focuses on nationalism's role in justifying and consolidating state power and domination. Through its unifying goal, nationalism strives for centralisation (both in specific territories and in a ruling elite of individuals) while it prepares a population for capitalist exploitation. Within anarchism, this subject has been extensively discussed by Rudolf Rocker in his book titled Nationalism and Culture and by the works of Fredy Perlman such as Against His-Story, Against Leviathan and The Continuing Appeal of Nationalism.

The failure of revolutions in Germany and Hungary in the 1918–1920 years ended Bolshevik hopes for an imminent world revolution and led to the promotion of the doctrine of socialism in one country by Joseph Stalin. In the first edition of his book titled Osnovy Leninizma (Foundations of Leninism, 1924), Stalin argued that revolution in one country is insufficient. By the end of that year in the second edition of the book, he argued that the "proletariat can and must build the socialist society in one country". In April 1925, Nikolai Bukharin elaborated on the issue in his brochure titled Can We Build Socialism in One Country in the Absence of the Victory of the West-European Proletariat?, whose position was adopted as state policy after Stalin's January 1926 article titled On the Issues of Leninism (К вопросам ленинизма) was published. This idea was opposed by Leon Trotsky and his supporters, who declared the need for an international "permanent revolution" and condemned Stalin for betraying the goals and ideals of the socialist revolution. Various Fourth Internationalist groups around the world who describe themselves as Trotskyist see themselves as standing in this tradition while Maoist China formally supported the theory of socialism in one country.

European social democrats strongly support Europeanism and supranational integration within the European Union, although there is a minority of nationalists and Eurosceptics on the left. Several scholars have linked this form of left-wing nationalism to the pressure generated by economic integration with other countries, often encouraged by neoliberal free trade agreements. This view is sometimes used to justify hostility towards supranational organizations. Left-wing nationalism can also refer to any form of nationalism which emphasizes a leftist working-class populist agenda that seeks to overcome exploitation or oppression by other nations. Many Third World anti-colonialist movements have adopted leftist and socialist ideas. Third-Worldism is a tendency within leftist thought that regards the division between First World and Second World developed countries and Third World developing countries as being of high political importance. This tendency supports decolonization and national liberation movements against imperialism by capitalists. Third-Worldism is closely connected with African socialism, Latin American socialism, Maoism, pan-Africanism and pan-Arabism. Several left-wing groups in the developing world such as the Zapatista Army of National Liberation in Mexico, the Abahlali baseMjondolo in South Africa and the Naxalites in India have argued that the First World and the Second World Left takes a racist and paternalistic attitude towards liberation movements in the Third World.

Religion

The original French Left was firmly anti-clerical, strongly opposing the influence of the Roman Catholic Church and supporting atheism and the separation of church and state, ushering in a policy known as laïcité. Karl Marx asserted that "[r]eligion is the sigh of the oppressed creature, the heart of a heartless world, and the soul of soulless conditions. It is the opium of the people". In Soviet Russia, the Bolsheviks under Vladimir Lenin originally embraced an ideological principle which professed that all religion would eventually atrophy and resolved to eradicate organized Christianity and other religious institutions. In 1918, 10 Russian Orthodox hierarchs were summarily executed by a firing squad, and children were deprived of any religious education outside of the home.

Today in the Western world, those on the Left generally support secularization and the separation of church and state. However, religious beliefs have also been associated with many left-wing movements such as the progressive movement, the Social Gospel movement, the civil rights movement, the anti-war movement, the anti-capital punishment movement and Liberation Theology. Early utopian socialist thinkers such as Robert Owen, Charles Fourier and the Comte de Saint-Simon based their theories of socialism upon Christian principles. From St. Augustine of Hippo's City of God through St. Thomas More's Utopia, major Christian writers defended ideas that socialists found agreeable and advocated for. Other common leftist concerns such as pacifism, social justice, racial equality, human rights and the rejection of capitalism and excessive wealth can be found in the Holy Bible.

In the late 19th century, the Social Gospel movement arose, particularly among Anglicans, Lutherans, Methodists and Baptists in North America and Britain which integrated progressive and socialist thought with Christianity through faith-based social activism, promoted by movements such as Christian anarchism, Christian socialism and Christian communism. In the 20th century, the theology of liberation and Creation Spirituality was championed by several scholars and priests, such as Gustavo Gutierrez and Matthew Fox. Other left-wing religious movements include Buddhist socialism, Jewish socialism and Islamic socialism. There have been alliances between the left and anti-war Muslims, such as the Respect Party and the Stop the War Coalition in Britain. In France, the left has been divided over moves to ban the hijab from schools, with some leftists supporting a ban based on the separation of church and state in accordance with the principle of laïcité and other leftists opposing the prohibition based on personal and religious freedom.

Social progressivism and counterculture

Social progressivism is another common feature of modern leftism, particularly in the United States, where social progressives played an important role in the abolition of slavery, the enshrinement of women's suffrage in the United States Constitution, and the protection of civil rights, LGBTQ rights, women's rights and multiculturalism. Progressives have both advocated for alcohol prohibition legislation and worked towards its repeal in the mid to late 1920s and early 1930s. Current positions associated with social progressivism in the Western world include strong opposition to the death penalty, torture, mass surveillance, and the war on drugs, and support for abortion rights, cognitive liberty, LGBTQ rights including legal recognition of same-sex marriage, same-sex adoption of children, the right to change one's legal gender, distribution of contraceptives, and public funding of embryonic stem-cell research. The desire for an expansion of social and civil liberties often overlaps that of the libertarian movement. Public education was a subject of great interest to groundbreaking social progressives such as Lester Frank Ward and John Dewey, who believed that a democratic society and system of government was practically impossible without a universal and comprehensive nationwide system of education.

Various counterculture and anti-war movements in the 1960s and 1970s were associated with the New Left. Unlike the earlier leftist focus on labour union activism and a proletarian revolution, the New Left instead adopted a broader definition of political activism commonly called social activism. The New Left in the United States is associated with the hippie movement, mass protest movements on school campuses and a broadening of focus from protesting class-based oppression to include issues such as gender, race and sexual orientation. The British New Left was an intellectually driven movement which attempted to correct the perceived errors of the Old Left. The New Left opposed prevailing authoritarian structures in society which it designated as "The Establishment" and became known as the "Anti-Establishment". The New Left did not seek to recruit industrial workers en masse, but instead concentrated on a social activist approach to organization, convinced that they could be the source for a better kind of social revolution. This view has been criticized by several Marxists, especially Trotskyists, who characterized this approach as "substitutionism" which they described as a misguided and non-Marxist belief that other groups in society could "substitute" for and "replace" the revolutionary agency of the working class.

Many early feminists and advocates of women's rights were considered a part of the Left by their contemporaries. Feminist pioneer Mary Wollstonecraft was influenced by Thomas Paine. Many notable leftists have been strong supporters of gender equality such as Marxist philosophers and activists Rosa Luxemburg, Clara Zetkin and Alexandra Kollontai, anarchist philosophers and activists such as Virginia Bolten, Emma Goldman and Lucía Sánchez Saornil and democratic socialist philosophers and activists such as Helen Keller and Annie Besant. However, Marxists such as Rosa Luxemburg, Clara Zetkin, and Alexandra Kollontai, who are supporters of radical social equality for women and have rejected and opposed liberal feminism because they considered it to be a capitalist bourgeois ideology. Marxists were responsible for organizing the first International Working Women's Day events.

The women's liberation movement is closely connected to the New Left and other new social movements which openly challenged the orthodoxies of the Old Left. Socialist feminism as exemplified by the Freedom Socialist Party and Radical Women and Marxist feminism, spearheaded by Selma James, saw themselves as a part of the Left that challenges male-dominated and sexist structures within the Left. The connection between left-wing ideologies and the struggle for LGBTQ rights also has an important history. Prominent socialists who were involved in early struggles for LGBTQ rights include Edward Carpenter, Oscar Wilde, Harry Hay, Bayard Rustin and Daniel Guérin, among others. The New Left is also strongly supportive of LGBTQ rights and liberation, having been instrumental in the founding of the LGBTQ rights movement in the aftermath of the Stonewall Uprising of 1969 and contemporary leftist activists and socialist countries such as Cuba are actively supportive of LGBTQ+ people and are involved in the struggle for LGBTQ+ rights and equality.

History

In politics, the term Left derives from the French Revolution as the political groups opposed to the royal veto privilege (Montagnard and Jacobin deputies from the Third Estate) generally sat to the left of the presiding member's chair in parliament while the ones in favour of the royal veto privilege sat on its right. That habit began in the French Estates General of 1789. Throughout the 19th century, the main line dividing Left and Right was between supporters of the French republic and those of the monarchy's privileges. The June Days uprising during the Second Republic was an attempt by the Left to re-assert itself after the 1848 Revolution, but only a small portion of the population supported this.

In the mid-19th century, nationalism, socialism, democracy and anti-clericalism became key features of the French Left. After Napoleon III's 1851 coup and the subsequent establishment of the Second Empire, Marxism began to rival radical republicanism and utopian socialism as a force within left-wing politics. The influential Communist Manifesto by Karl Marx and Friedrich Engels, published amidst the wave of revolutions of 1848 across Europe, asserted that all of human history is defined by class struggle. They predicted that a proletarian revolution would eventually overthrow bourgeois capitalism and create a stateless, moneyless and classless communist society. It was in this period that the word wing was appended to both Left and Right.

The International Workingmen's Association (1864–1876), sometimes called the First International, brought together delegates from many different countries, with many different views about how to reach a classless and stateless society. Following a split between supporters of Marx and Mikhail Bakunin, anarchists formed the International Workers' Association (IWA–AIT). The Second International (1888–1916) became divided over the issue of World War I. Those who opposed the war, among them Vladimir Lenin and Rosa Luxemburg, saw themselves as further to the left.

In the United States, leftists such as social liberals, progressives and trade unionists were influenced by the works of Thomas Paine, who introduced the concept of asset-based egalitarianism which theorises that social equality is possible by a redistribution of resources. After the Reconstruction era in the aftermath of the American Civil War, the phrase "the Left" was used to describe those who supported trade unions, the civil rights movement and the anti-war movement. More recently, left-wing and right-wing have often been used as synonyms for the Democratic and Republican parties, or as synonyms for liberalism and conservatism, respectively.

Since the Right was populist, both in the Western and the Eastern Bloc anything viewed as avant-garde art was called leftist across Europe, thus the identification of Picasso's Guernica as "leftist" in Europe and the condemnation of the Russian composer Shostakovich's opera (The Lady Macbeth of Mtsensk District) in Pravda as follows: "Here we have 'leftist' confusion instead of natural, human music".

Types

The spectrum of left-wing politics ranges from centre-left to far-left or ultra-left. The term centre-left describes a position within the political mainstream that accepts capitalism and a market economy. The terms far-left and ultra-left are used for positions that are more radical, more strongly rejecting capitalism and mainstream representative democracy, instead advocating for a socialist society based on economic democracy and direct democracy, representing economic, political and social democracy. The centre-left includes social democrats, social liberals, progressives and greens. Centre-left supporters accept market allocation of resources in a mixed economy with an empowered public sector and a thriving private sector. Centre-left policies tend to favour limited state intervention in matters pertaining to the public interest.

In several countries, the terms far-left and radical left have been associated with many varieties of anarchism, autonomism and communism. They have been used to describe groups that advocate anti-capitalism and eco-terrorism. In France, a distinction is made between the centre-left and the left represented by the Socialist Party and the French Communist Party and the far-left as represented by anarcho-communists, Maoists and Trotskyists. The United States Department of Homeland Security defines "left-wing extremism" as groups that "seek to bring about change through violent revolution, rather than through established political processes". In China, the term Chinese New Left denotes those who oppose the economic reforms enacted by Deng Xiaoping in the 1980s and 1990s, favour instead the restoration of Maoist policies and the immediate transition to a socialist economy. In the Western world, the term New Left is used for social and cultural politics.

In the United Kingdom during the 1980s, the term hard left was applied to supporters of Tony Benn such as the Campaign Group and those involved in the London Labour Briefing newspaper as well as Trotskyist groups such as Militant and the Alliance for Workers' Liberty. In the same period, the term soft left was applied to supporters of the British Labour Party who were perceived to be more moderate and closer to the centre, accepting Keynesianism. Under the leadership of Tony Blair and Gordon Brown, the Labour Party adopted the Third Way and rebranded itself as New Labour in order to promote the notion that it was less left-wing than it had been in the past to accommodate the neoliberal trend arising since the 1970s with the displacement of Keynesianism and post-war social democracy. One of the first actions of Ed Miliband, the Labour Party leader who succeeded Blair and Brown, was the rejection of the New Labour label and a promise to abandon the Third Way and turn back to the left. However, Labour's voting record in the House of Commons from 2010 to 2015 indicated that the Labour Party under Miliband had maintained the same distance from the left as it did under Blair. In contrast, the election of Jeremy Corbyn as the Labour Party leader was viewed by scholars and political commentators as Labour turning back toward its more classical socialist roots, rejecting neoliberalism and the Third Way whilst supporting a democratic socialist society and an end to austerity measures.

DNA barcoding

From Wikipedia, the free encyclopedia

DNA barcoding scheme

DNA barcoding is a method of species identification using a short section of DNA from a specific gene or genes. The premise of DNA barcoding is that, by comparison with a reference library of such DNA sections (also called "sequences"), an individual sequence can be used to uniquely identify an organism to species, in the same way that a supermarket scanner uses the familiar black stripes of the UPC barcode to identify an item in its stock against its reference database. These "barcodes" are sometimes used in an effort to identify unknown species, parts of an organism, or simply to catalog as many taxa as possible, or to compare with traditional taxonomy in an effort to determine species boundaries.

Different gene regions are used to identify the different organismal groups using barcoding. The most commonly used barcode region for animals and some protists is a portion of the cytochrome c oxidase I (COI or COX1) gene, found in mitochondrial DNA. Other genes suitable for DNA barcoding are the internal transcribed spacer (ITS) rRNA often used for fungi and RuBisCO used for plants. Microorganisms are detected using different gene regions. The 16S rRNA gene for example is widely used in identification of prokaryotes, whereas the 18S rRNA gene is mostly used for detecting microbial eukaryotes. These gene regions are chosen because they have less intraspecific (within species) variation than interspecific (between species) variation, which is known as the "Barcoding Gap".

Some applications of DNA barcoding include: identifying plant leaves even when flowers or fruits are not available; identifying pollen collected on the bodies of pollinating animals; identifying insect larvae which may have fewer diagnostic characters than adults; or investigating the diet of an animal based on its stomach content, saliva or feces. When barcoding is used to identify organisms from a sample containing DNA from more than one organism, the term DNA metabarcoding is used, e.g. DNA metabarcoding of diatom communities in rivers and streams, which is used to assess water quality.

Background

DNA barcoding techniques were developed from early DNA sequencing work on microbial communities using the 5S rRNA gene. In 2003, specific methods and terminology of modern DNA barcoding were proposed as a standardized method for identifying species, as well as potentially allocating unknown sequences to higher taxa such as orders and phyla, in a paper by Paul D.N. Hebert et al. from the University of Guelph, Ontario, Canada. Hebert and his colleagues demonstrated the utility of the cytochrome c oxidase I (COI) gene, first utilized by Folmer et al. in 1994, using their published DNA primers as a tool for phylogenetic analyses at the species levels as a suitable discriminatory tool between metazoan invertebrates. The "Folmer region" of the COI gene is commonly used for distinction between taxa based on its patterns of variation at the DNA level. The relative ease of retrieving the sequence, and variability mixed with conservation between species, are some of the benefits of COI. Calling the profiles "barcodes", Hebert et al. envisaged the development of a COI database that could serve as the basis for a "global bioidentification system".

Methodology

Sampling and preservation

Barcoding can be done from tissue from a target specimen, from a mixture of organisms (bulk sample), or from DNA present in environmental samples (e.g. water or soil). The methods for sampling, preservation or analysis differ between those different types of sample.

Tissue samples

To barcode a tissue sample from the target specimen, a small piece of skin, a scale, a leg or antenna is likely to be sufficient (depending on the size of the specimen). To avoid contamination, it is necessary to sterilize used tools between samples. It is recommended to collect two samples from one specimen, one to archive, and one for the barcoding process. Sample preservation is crucial to overcome the issue of DNA degradation.

Bulk samples

A bulk sample is a type of environmental sample containing several organisms from the taxonomic group under study. The difference between bulk samples (in the sense used here) and other environmental samples is that the bulk sample usually provides a large quantity of good-quality DNA. Examples of bulk samples include aquatic macroinvertebrate samples collected by kick-net, or insect samples collected with a Malaise trap. Filtered or size-fractionated water samples containing whole organisms like unicellular eukaryotes are also sometimes defined as bulk samples. Such samples can be collected by the same techniques used to obtain traditional samples for morphology-based identification.

eDNA samples

The environmental DNA (eDNA) method is a non-invasive approach to detect and identify species from cellular debris or extracellular DNA present in environmental samples (e.g. water or soil) through barcoding or metabarcoding. The approach is based on the fact that every living organism leaves DNA in the environment, and this environmental DNA can be detected even for organisms that are at very low abundance. Thus, for field sampling, the most crucial part is to use DNA-free material and tools on each sampling site or sample to avoid contamination, if the DNA of the target organism(s) is likely to be present in low quantities. On the other hand, an eDNA sample always includes the DNA of whole-cell, living microorganisms, which are often present in large quantities. Therefore, microorganism samples taken in the natural environment also are called eDNA samples, but contamination is less problematic in this context due to the large quantity of target organisms. The eDNA method is applied on most sample types, like water, sediment, soil, animal feces, stomach content or blood from e.g. leeches.

DNA extraction, amplification and sequencing

DNA barcoding requires that DNA in the sample is extracted. Several different DNA extraction methods exist, and factors like cost, time, sample type and yield affect the selection of the optimal method.

When DNA from organismal or eDNA samples is amplified using polymerase chain reaction (PCR), the reaction can be affected negatively by inhibitor molecules contained in the sample. Removal of these inhibitors is crucial to ensure that high quality DNA is available for subsequent analyzing.

Amplification of the extracted DNA is a required step in DNA barcoding. Typically, only a small fragment of the total DNA material is sequenced (typically 400–800 base pairs) to obtain the DNA barcode. Amplification of eDNA material is usually focused on smaller fragment sizes (<200 base pairs), as eDNA is more likely to be fragmented than DNA material from other sources. However, some studies argue that there is no relationship between amplicon size and detection rate of eDNA.

HiSeq sequencers at SciLIfeLab in Uppsala, Sweden. The photo was taken during the excursion of SLU course PNS0169 in March 2019.

When the DNA barcode marker region has been amplified, the next step is to sequence the marker region using DNA sequencing methods. Many different sequencing platforms are available, and technical development is proceeding rapidly.

Marker selection

A schematic view of primers and target region, demonstrated on 16S rRNA gene in Pseudomonas. As primers, one typically selects short conserved sequences with low variability, which can thus amplify most or all species in the chosen target group. The primers are used to amplify a highly variable target region in between the two primers, which is then used for species discrimination. Modified from »Variable Copy Number, Intra-Genomic Heterogeneities and Lateral Transfers of the 16S rRNA Gene in Pseudomonas« by Bodilis, Josselin; Nsigue-Meilo, Sandrine; Besaury, Ludovic; Quillet, Laurent, used under CC BY, available from: https://www.researchgate.net/figure/Hypervariable-regions-within-the-16S-rRNA-gene-in-Pseudomonas-The-plotted-line-reflects_fig2_224832532.

Markers used for DNA barcoding are called barcodes. In order to successfully characterize species based on DNA barcodes, selection of informative DNA regions is crucial. A good DNA barcode should have low intra-specific and high inter-specific variability and possess conserved flanking sites for developing universal PCR primers for wide taxonomic application. The goal is to design primers that will detect and distinguish most or all the species in the studied group of organisms (high taxonomic resolution). The length of the barcode sequence should be short enough to be used with current sampling source, DNA extraction, amplification and sequencing methods.

Ideally, one gene sequence would be used for all taxonomic groups, from viruses to plants and animals. However, no such gene region has been found yet, so different barcodes are used for different groups of organisms, or depending on the study question.

For animals, the most widely used barcode is mitochondrial cytochrome C oxidase I (COI) locus. Other mitochondrial genes, such as Cytb, 12S or 18S are also used. Mitochondrial genes are preferred over nuclear genes because of their lack of introns, their haploid mode of inheritance and their limited recombination. Moreover, each cell has various mitochondria (up to several thousand) and each of them contains several circular DNA molecules. Mitochondria can therefore offer abundant source of DNA even when sample tissue is limited.

In plants, however, mitochondrial genes are not appropriate for DNA barcoding because they exhibit low mutation rates. A few candidate genes have been found in the chloroplast genome, the most promising being maturase K gene (matK) by itself or in association with other genes. Multi-locus markers such as ribosomal internal transcribed spacers (ITS DNA) along with matK, rbcL, trnH or other genes have also been used for species identification. The best discrimination between plant species has been achieved when using two or more chloroplast barcodes.

For bacteria, the small subunit of ribosomal RNA (16S) gene can be used for different taxa, as it is highly conserved. Some studies suggest COI, type II chaperonin (cpn60) or β subunit of RNA polymerase (rpoB) also could serve as bacterial DNA barcodes.

Barcoding fungi is more challenging, and more than one primer combination might be required. The COI marker performs well in certain fungi groups, but not equally well in others. Therefore, additional markers are being used, such as ITS rDNA and the large subunit of nuclear ribosomal RNA (28S LSU rRNA).

Within the group of protists, various barcodes have been proposed, such as the D1–D2 or D2–D3 regions of 28S rDNA, V4 subregion of 18S rRNA gene, ITS rDNA and COI. Additionally, some specific barcodes can be used for photosynthetic protists, for example the large subunit of ribulose-1,5-bisphosphate carboxylase-oxygenase gene (rbcL) and the chloroplastic 23S rRNA gene.

Markers that have been used for DNA barcoding in different organism groups, modified from Purty and Chatterjee.
Organism group Marker gene/locus
Animals COI, Cytb, 12S, 16S
Plants matK, rbcL, psbA-trnH, ITS
Bacteria COI, rpoB, 16S, cpn60, tuf, RIF, gnd
Fungi ITS, TEF1α, RPB1, RPB2, 18S, 28S
Protists ITS, COI, rbcL, 18S, 28S, 23S

Reference libraries and bioinformatics

Reference libraries are used for the taxonomic identification, also called annotation, of sequences obtained from barcoding or metabarcoding. These databases contain the DNA barcodes assigned to previously identified taxa. Most reference libraries do not cover all species within an organism group, and new entries are continually created. In the case of macro- and many microorganisms (such as algae), these reference libraries require detailed documentation (sampling location and date, person who collected it, image, etc.) and authoritative taxonomic identification of the voucher specimen, as well as submission of sequences in a particular format. However, such standards are fulfilled for only a small number of species. The process also requires the storage of voucher specimens in museum collections, herbaria and other collaborating institutions. Both taxonomically comprehensive coverage and content quality are important for identification accuracy. In the microbial world, there is no DNA information for most species names, and many DNA sequences cannot be assigned to any Linnaean binomial. Several reference databases exist depending on the organism group and the genetic marker used. There are smaller, national databases (e.g. FinBOL), and large consortia like the International Barcode of Life Project (iBOL).

BOLD

Launched in 2007, the Barcode of Life Data System (BOLD) is one of the biggest databases, containing more than 450 000 BINs (Barcode Index Numbers) in 2019. It is a freely accessible repository for the specimen and sequence records for barcode studies, and it is also a workbench aiding the management, quality assurance and analysis of barcode data. The database mainly contains BIN records for animals based on the COI genetic marker.

UNITE

The UNITE database was launched in 2003 and is a reference database for the molecular identification of fungal species with the internal transcribed spacer (ITS) genetic marker region. This database is based on the concept of species hypotheses: you choose the % at which you want to work, and the sequences are sorted in comparison to sequences obtained from voucher specimens identified by experts.

Diat.barcode

Diat.barcode database was first published under the name R-syst::diatom in 2016 starting with data from two sources: the Thonon culture collection (TCC) in the hydrobiological station of the French National Institute for Agricultural Research (INRA), and from the NCBI (National Center for Biotechnology Information) nucleotide database. Diat.barcode provides data for two genetic markers, rbcL (Ribulose-1,5-bisphosphate carboxylase/oxygenase) and 18S (18S ribosomal RNA). The database also involves additional, trait information of species, like morphological characteristics (biovolume, size dimensions, etc.), life-forms (mobility, colony-type, etc.) or ecological features (pollution sensitivity, etc.).

Bioinformatic analysis

In order to obtain well structured, clean and interpretable data, raw sequencing data must be processed using bioinformatic analysis. The FASTQ file with the sequencing data contains two types of information: the sequences detected in the sample (FASTA file) and a quality file with quality scores (PHRED scores) associated with each nucleotide of each DNA sequence. The PHRED scores indicate the probability with which the associated nucleotide has been correctly scored.

PHRED quality score and the associated certainty level
10 90%
20 99%
30 99.9%
40 99.99%
50 99.999%

In general, the PHRED score decreases towards the end of each DNA sequence. Thus some bioinformatics pipelines simply cut the end of the sequences at a defined threshold.

Some sequencing technologies, like MiSeq, use paired-end sequencing during which sequencing is performed from both directions producing better quality. The overlapping sequences are then aligned into contigs and merged. Usually, several samples are pooled in one run, and each sample is characterized by a short DNA fragment, the tag. In a demultiplexing step, sequences are sorted using these tags to reassemble the separate samples. Before further analysis, tags and other adapters are removed from the barcoding sequence DNA fragment. During trimming, the bad quality sequences (low PHRED scores), or sequences that are much shorter or longer than the targeted DNA barcode, are removed. The following dereplication step is the process where all of the quality-filtered sequences are collapsed into a set of unique reads (individual sequence units ISUs) with the information of their abundance in the samples. After that, chimeras (i.e. compound sequences formed from pieces of mixed origin) are detected and removed. Finally, the sequences are clustered into OTUs (Operational Taxonomic Units), using one of many clustering strategies. The most frequently used bioinformatic software include Mothur, Uparse, Qiime, Galaxy, Obitools, JAMP, Barque, and DADA2.

Comparing the abundance of reads, i.e. sequences, between different samples is still a challenge because both the total number of reads in a sample as well as the relative amount of reads for a species can vary between samples, methods, or other variables. For comparison, one may then reduce the number of reads of each sample to the minimal number of reads of the samples to be compared – a process called rarefaction. Another way is to use the relative abundance of reads.

Species identification and taxonomic assignment

The taxonomic assignment of the OTUs to species is achieved by matching of sequences to reference libraries. The Basic Local Alignment Search Tool (BLAST) is commonly used to identify regions of similarity between sequences by comparing sequence reads from the sample to sequences in reference databases. If the reference database contains sequences of the relevant species, then the sample sequences can be identified to species level. If a sequence cannot be matched to an existing reference library entry, DNA barcoding can be used to create a new entry.

In some cases, due to the incompleteness of reference databases, identification can only be achieved at higher taxonomic levels, such as assignment to a family or class. In some organism groups such as bacteria, taxonomic assignment to species level is often not possible. In such cases, a sample may be assigned to a particular operational taxonomic unit (OTU).

Applications

Applications of DNA barcoding include identification of new species, safety assessment of food, identification and assessment of cryptic species, detection of alien species, identification of endangered and threatened species, linking egg and larval stages to adult species, securing intellectual property rights for bioresources, framing global management plans for conservation strategies and elucidate feeding niches. DNA barcode markers can be applied to address basic questions in systematics, ecology, evolutionary biology and conservation, including community assembly, species interaction networks, taxonomic discovery, and assessing priority areas for environmental protection.

Identification of species

Specific short DNA sequences or markers from a standardized region of the genome can provide a DNA barcode for identifying species. Molecular methods are especially useful when traditional methods are not applicable. DNA barcoding has great applicability in identification of larvae for which there are generally few diagnostic characters available, and in association of different life stages (e.g. larval and adult) in many animals. Identification of species listed in the Convention of the International Trade of Endangered Species (CITES) appendixes using barcoding techniques is used in monitoring of illegal trade.

Detection of invasive species

Alien species can be detected via barcoding. Barcoding can be suitable for detection of species in e.g. border control, where rapid and accurate morphological identification is often not possible due to similarities between different species, lack of sufficient diagnostic characteristics and/or lack of taxonomic expertise. Barcoding and metabarcoding can also be used to screen ecosystems for invasive species, and to distinguish between an invasive species and native, morphologically similar, species.

Delimiting cryptic species

DNA barcoding enables the identification and recognition of cryptic species. The results of DNA barcoding analyses depend however upon the choice of analytical methods, so the process of delimiting cryptic species using DNA barcodes can be as subjective as any other form of taxonomy. Hebert et al. (2004) concluded that the butterfly Astraptes fulgerator in north-western Costa Rica actually consists of 10 different species. These results, however, were subsequently challenged by Brower (2006), who pointed out numerous serious flaws in the analysis, and concluded that the original data could support no more than the possibility of three to seven cryptic taxa rather than ten cryptic species. Smith et al. (2007) used cytochrome c oxidase I DNA barcodes for species identification of the 20 morphospecies of Belvosia parasitoid flies (Diptera: Tachinidae) reared from caterpillars (Lepidoptera) in Area de Conservación Guanacaste (ACG), northwestern Costa Rica. These authors discovered that barcoding raises the species count to 32, by revealing that each of the three parasitoid species, previously considered as generalists, actually are arrays of highly host-specific cryptic species. For 15 morphospecies of polychaetes within the deep Antarctic benthos studied through DNA barcoding, cryptic diversity was found in 50% of the cases. Furthermore, 10 previously overlooked morphospecies were detected, increasing the total species richness in the sample by 233%.

Barcoding is a tool to vouch for food quality. Here, DNA from traditional Norwegian Christmas food is extracted at the molecular systematic lab at NTNU University Museum.

Diet analysis and food web application

DNA barcoding and metabarcoding can be useful in diet analysis studies, and is typically used if prey specimens cannot be identified based on morphological characters. There is a range of sampling approaches in diet analysis: DNA metabarcoding can be conducted on stomach contents, feces, saliva or whole body analysis. In fecal samples or highly digested stomach contents, it is often not possible to distinguish tissue from single species, and therefore metabarcoding can be applied instead. Feces or saliva represent non-invasive sampling approaches, while whole body analysis often means that the individual needs to be killed first. For smaller organisms, sequencing for stomach content is then often done by sequencing the entire animal.

Barcoding for food safety

DNA barcoding represents an essential tool to evaluate the quality of food products. The purpose is to guarantee food traceability, to minimize food piracy, and to valuate local and typical agro-food production. Another purpose is to safeguard public health; for example, metabarcoding offers the possibility to identify groupers causing Ciguatera fish poisoning from meal remnants, or to separate poisonous mushrooms from edible ones (Ref).

Biomonitoring and ecological assessment

DNA barcoding can be used to assess the presence of endangered species for conservation efforts (Ref), or the presence of indicator species reflective to specific ecological conditions (Ref), for example excess nutrients or low oxygen levels.

Potentials and shortcomings

Potentials

Traditional bioassessment methods are well established internationally, and serve biomonitoring well, as for example for aquatic bioassessment within the EU Directives WFD and MSFD. However, DNA barcoding could improve traditional methods for the following reasons; DNA barcoding (i) can increase taxonomic resolution and harmonize the identification of taxa which are difficult to identify or lack experts, (ii) can more accurately/precisely relate environmental factors to specific taxa (iii) can increase comparability among regions, (iv) allows for the inclusion of early life stages and fragmented specimens, (v) allows delimitation of cryptic/rare species (vi) allows for development of new indices e.g. rare/cryptic species which may be sensitive/tolerant to stressors, (vii) increases the number of samples which can be processed and reduces processing time resulting in increased knowledge of species ecology, (viii) is a non-invasive way of monitoring when using eDNA methods.

Time and cost

DNA barcoding is faster than traditional morphological methods all the way from training through to taxonomic assignment. It takes less time to gain expertise in DNA methods than becoming an expert in taxonomy. In addition, the DNA barcoding workflow (i.e. from sample to result) is generally quicker than traditional morphological workflow and allows the processing of more samples.

Taxonomic resolution

DNA barcoding allows the resolution of taxa from higher (e.g. family) to lower (e.g. species) taxonomic levels, that are otherwise too difficult to identify using traditional morphological methods, like e.g. identification via microscopy. For example, Chironomidae (the non-biting midge) are widely distributed in both terrestrial and freshwater ecosystems. Their richness and abundance make them important for ecological processes and networks, and they are one of many invertebrate groups used in biomonitoring. Invertebrate samples can contain as many as 100 species of chironomids which often make up as much as 50% of a sample. Despite this, they are usually not identified below the family level because of the taxonomic expertise and time required. This may result in different chironomid species with different ecological preferences grouped together, resulting in inaccurate assessment of water quality.

DNA barcoding provides the opportunity to resolve taxa, and directly relate stressor effects to specific taxa such as individual chironomid species. For example, Beermann et al. (2018) DNA barcoded Chironomidae to investigate their response to multiple stressors; reduced flow, increased fine-sediment and increased salinity. After barcoding, it was found that the chironomid sample consisted of 183 Operational Taxonomic Units (OTUs), i.e. barcodes (sequences) that are often equivalent to morphological species. These 183 OTUs displayed 15 response types rather than the previously reported  two response types recorded when all chironomids were grouped together in the same multiple stressor study. A similar trend was discovered in a study by Macher et al. (2016) which discovered cryptic diversity within the New Zealand mayfly species Deleatidium sp. This study found different response patterns of 12 molecular distinct OTUs to stressors which may change the consensus that this mayfly is sensitive to pollution.

Shortcomings

Despite the advantages offered by DNA barcoding, it has also been suggested that DNA barcoding is best used as a complement to traditional morphological methods. This recommendation is based on multiple perceived challenges.

Physical parameters

It is not completely straightforward to connect DNA barcodes with ecological preferences of the barcoded taxon in question, as is needed if barcoding is to be used for biomonitoring. For example, detecting target DNA in aquatic systems depends on the concentration of DNA molecules at a site, which in turn can be affected by many factors. The presence of DNA molecules also depends on dispersion at a site, e.g. direction or strength of currents. It is not really known how DNA moves around in streams and lakes, which makes sampling difficult. Another factor might be the behavior of the target species, e.g. fish can have seasonal changes of movements, crayfish or mussels will release DNA in larger amounts just at certain times of their life (moulting, spawning). For DNA in soil, even less is known about distribution, quantity or quality.

The major limitation of the barcoding method is that it relies on barcode reference libraries for the taxonomic identification of the sequences. The taxonomic identification is accurate only if a reliable reference is available. However, most databases are still incomplete, especially for smaller organisms e.g. fungi, phytoplankton, nematoda etc. In addition, current databases contain misidentifications, spelling mistakes and other errors. There is massive curation and completion effort around the databases for all organisms necessary, involving large barcoding projects (for example the iBOL project for the Barcode of Life Data Systems (BOLD) reference database). However, completion and curation are difficult and time-consuming. Without vouchered specimens, there can be no certainty about whether the sequence used as a reference is correct.

DNA sequence databases like GenBank contain many sequences that are not tied to vouchered specimens (for example, herbarium specimens, cultured cell lines, or sometimes images). This is problematic in the face of taxonomic issues such as whether several species should be split or combined, or whether past identifications were sound. Reusing sequences, not tied to vouchered specimens, of initially misidentified organism may support incorrect conclusions and must be avoided. Therefore, best practice for DNA barcoding is to sequence vouchered specimens. For many taxa, it can be however difficult to obtain reference specimens, for example with specimens that are difficult to catch, available specimens are poorly conserved, or adequate taxonomic expertise is lacking.

Importantly, DNA barcodes can also be used to create interim taxonomy, in which case OTUs can be used as substitutes for traditional Latin binomials – thus significantly reducing dependency on fully populated reference databases.

Technological bias

DNA barcoding also carries methodological bias, from sampling to bioinformatics data analysis. Beside the risk of contamination of the DNA sample by PCR inhibitors, primer bias is one of the major sources of errors in DNA barcoding. The isolation of an efficient DNA marker and the design of primers is a complex process and considerable effort has been made to develop primers for DNA barcoding in different taxonomic groups. However, primers will often bind preferentially to some sequences, leading to differential primer efficiency and specificity and unrepresentative communities’ assessment and richness inflation. Thus, the composition of the sample's communities sequences is mainly altered at the PCR step.  Besides, PCR replication is often required, but leads to an exponential increase in the risk of contamination. Several studies have highlighted the possibility to use mitochondria-enriched samples  or PCR-free approaches to avoid these biases, but as of today, the DNA metabarcoding technique is still based on the sequencing of amplicons. Other bias enter the picture during the sequencing and during the bioinformatic processing of the sequences, like the creation of chimeras.

Lack of standardization

Even as DNA barcoding is more widely used and applied, there is no agreement concerning the methods for DNA preservation or extraction, the choices of DNA markers and primers set, or PCR protocols. The parameters of bioinformatics pipelines (for example OTU clustering, taxonomic assignment algorithms or thresholds etc.) are at the origin of much debate among DNA barcoding users. Sequencing technologies are also rapidly evolving, together with the tools for the analysis of the massive amounts of DNA data generated, and standardization of the methods is urgently needed to enable collaboration and data sharing at greater spatial and time-scale. This standardisation of barcoding methods at the European scale is part of the objectives of the European COST Action DNAqua-net and is also addressed by CEN (the European Committee for Standardization).

Another criticism of DNA barcoding is its limited efficiency for accurate discrimination below species level (for example, to distinguish between varieties), for hybrid detection, and that it can be affected by evolutionary rates (Ref needed).

Mismatches between conventional (morphological) and barcode based identification

It is important to know that taxa lists derived by conventional (morphological) identification are not, and maybe never will be, directly comparable to taxa lists derived from barcode based identification because of several reasons. The most important cause is probably the incompleteness and lack of accuracy of the molecular reference databases preventing a correct taxonomic assignment of eDNA sequences. Taxa not present in reference databases will not be found by eDNA, and sequences linked to a wrong name will lead to incorrect identification. Other known causes are a different sampling scale and size between a traditional and a molecular sample, the possible analysis of dead organisms, which can happen in different ways for both methods depending on organism group, and the specific selection of identification in either method, i.e. varying taxonomical expertise or possibility to identify certain organism groups, respectively primer bias leading also to a potential biased analysis of taxa.

Estimates of richness/diversity

DNA Barcoding can result in an over or underestimate of species richness and diversity. Some studies suggest that artifacts (identification of species not present in a community) are a major cause of inflated biodiversity. The most problematic issue are taxa represented by low numbers of sequencing reads. These reads are usually removed during the data filtering process, since different studies suggest that most of these low-frequency reads may be artifacts. However, real rare taxa may exist among these low-abundance reads. Rare sequences can reflect unique lineages in communities which make them informative and valuable sequences. Thus, there is a strong need for more robust bioinformatics algorithms that allow the differentiation between informative reads and artifacts. Complete reference libraries would also allow a better testing of bioinformatics algorithms, by permitting a better filtering of artifacts (i.e. the removal of sequences lacking a counterpart among extant species) and therefore, it would be possible obtain a more accurate species assignment. Cryptic diversity can also result in inflated biodiversity as one morphological species may actually split into many distinct molecular sequences.

Metabarcoding

Differences in the standard methods for DNA barcoding and metabarcoding. While DNA barcoding points to find a specific species, metabarcoding looks for the whole community.
 

Metabarcoding is defined as the barcoding of DNA or eDNA (environmental DNA) that allows for simultaneous identification of many taxa within the same (environmental) sample, however often within the same organism group. The main difference between the approaches is that metabarcoding, in contrast to barcoding, does not focus on one specific organism, but instead aims to determine species composition within a sample.

Methodology

The metabarcoding procedure, like general barcoding, covers the steps of DNA extraction, PCR amplification, sequencing and data analysis. A barcode consists of a short variable gene region (for example, see different markers/barcodes) which is useful for taxonomic assignment flanked by highly conserved gene regions which can be used for primer design. Different genes are used depending if the aim is to barcode single species or metabarcoding several species. In the latter case, a more universal gene is used. Metabarcoding does not use single species DNA/RNA as a starting point, but DNA/RNA from several different organisms derived from one environmental or bulk sample.

Applications

Metabarcoding has the potential to complement biodiversity measures, and even replace them in some instances, especially as the technology advances and procedures gradually become cheaper, more optimized and widespread.

DNA metabarcoding applications include:

Advantages and challenges

The general advantages and shortcomings for barcoding reviewed above are valid also for metabarcoding. One particular drawback for metabarcoding studies is that there is no consensus yet regarding the optimal experimental design and bioinformatics criteria to be applied in eDNA metabarcoding. However, there are current joined attempts, like e.g. the EU COST network DNAqua-Net, to move forward by exchanging experience and knowledge to establish best-practice standards for biomonitoring.

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