Systematics

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A comparison of phylogenetic and phenetic (character-based) concepts Phylogenetics.svg
A comparison of phylogenetic and phenetic (character-based) concepts

Biological systematics is the study of the diversification of living forms, both past and present, and the relationships among living things through time. Relationships are visualized as evolutionary trees (synonyms: cladograms, phylogenetic trees, phylogenies). Phylogenies have two components: branching order (showing group relationships) and branch length (showing amount of evolution). Phylogenetic trees of species and higher taxa are used to study the evolution of traits (e.g., anatomical or molecular characteristics) and the distribution of organisms (biogeography). Systematics, in other words, is used to understand the evolutionary history of life on Earth.

Contents

The word systematics is derived from Latin word `systema', which means systematic arrangement of organisms. Carl Linnaeus used 'Systema Naturae' as the title of his book.

Branches and applications

In the study of biological systematics, researchers use the different branches to further understand the relationships between differing organisms. These branches are used to determine the applications and uses for modern day systematics.

Biological systematics classifies species by using three specific branches. Numerical systematics, or biometry, uses biological statistics to identify and classify animals. Biochemical systematics classifies and identifies animals based on the analysis of the material that makes up the living part of a cell—such as the nucleus, organelles, and cytoplasm. Experimental systematics identifies and classifies animals based on the evolutionary units that comprise a species, as well as their importance in evolution itself. Factors such as mutations, genetic divergence, and hybridization all are considered evolutionary units. [1]

With the specific branches, researchers are able to determine the applications and uses for modern-day systematics. These applications include:

Definition and relation with taxonomy

John Lindley provided an early definition of systematics in 1830, although he wrote of "systematic botany" rather than using the term "systematics". [2]

In 1970 Michener et al. defined "systematic biology" and "taxonomy" (terms that are often confused and used interchangeably) in relationship to one another as follows: [3]

Systematic biology (hereafter called simply systematics) is the field that (a) provides scientific names for organisms, (b) describes them, (c) preserves collections of them, (d) provides classifications for the organisms, keys for their identification, and data on their distributions, (e) investigates their evolutionary histories, and (f) considers their environmental adaptations. This is a field with a long history that in recent years has experienced a notable renaissance, principally with respect to theoretical content. Part of the theoretical material has to do with evolutionary areas (topics e and f above), the rest relates especially to the problem of classification. Taxonomy is that part of Systematics concerned with topics (a) to (d) above.

The term "taxonomy" was coined by Augustin Pyramus de Candolle while the term "systematic" was coined by Carl Linnaeus the father of taxonomy.

Taxonomy, systematic biology, systematics, biosystematics, scientific classification, biological classification, phylogenetics: At various times in history, all these words have had overlapping, related meanings. However, in modern usage, they can all be considered synonyms of each other.

For example, Webster's 9th New Collegiate Dictionary of 1987 treats "classification", "taxonomy", and "systematics" as synonyms. According to this work, the terms originated in 1790, c. 1828, and in 1888 respectively. Some[ who? ] claim systematics alone deals specifically with relationships through time, and that it can be synonymous with phylogenetics, broadly dealing with the inferred hierarchy[ citation needed ] of organisms. This means it would be a subset of taxonomy as it is sometimes regarded, but the inverse is claimed by others.[ who? ]

Europeans tend to use the terms "systematics" and "biosystematics" for the study of biodiversity as a whole, whereas North Americans tend to use "taxonomy" more frequently. [4] However, taxonomy, and in particular alpha taxonomy, is more specifically the identification, description, and naming (i.e. nomenclature) of organisms, [5] while "classification" focuses on placing organisms within hierarchical groups that show their relationships to other organisms. All of these biological disciplines can deal with both extinct and extant organisms.

Systematics uses taxonomy as a primary tool in understanding, as nothing about an organism's relationships with other living things can be understood without it first being properly studied and described in sufficient detail to identify and classify it correctly.[ citation needed ] Scientific classifications are aids in recording and reporting information to other scientists and to laymen. The systematist, a scientist who specializes in systematics, must, therefore, be able to use existing classification systems, or at least know them well enough to skilfully justify not using them.

Phenetics was an attempt to determine the relationships of organisms through a measure of overall similarity, making no distinction between plesiomorphies (shared ancestral traits) and apomorphies (derived traits). From the late-20th century onwards, it was superseded by cladistics, which rejects plesiomorphies in attempting to resolve the phylogeny of Earth's various organisms through time. Today's systematists generally make extensive use of molecular biology and of computer programs to study organisms.

Taxonomic characters

Taxonomic characters are the taxonomic attributes that can be used to provide the evidence from which relationships (the phylogeny) between taxa are inferred. [6] Kinds of taxonomic characters include: [7]

See also

Related Research Articles

Cladistics Method of biological systematics in evolutionary biology

Cladistics is an approach to biological classification in which organisms are categorized in groups ("clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is typically shared derived characteristics (synapomorphies) that are not present in more distant groups and ancestors. Theoretically, a common ancestor and all its descendants are part of the clade. However, from an empirical perspective, common ancestors are inferences based on a cladistic hypothesis of relationships of taxa whose character states can be observed. Importantly, all descendants stay in their overarching ancestral clade. For example, if the terms worms or fishes were used within a strict cladistic framework, these terms would include humans. Many of these terms are normally used paraphyletically, outside of cladistics, e.g. as a 'grade'. Radiation results in the generation of new subclades by bifurcation, but in practice sexual hybridization may blur very closely related groupings.

Clade Group of a common ancestor and all descendants

A clade, also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants - on a phylogenetic tree. Rather than the English term, the equivalent Latin term cladus is often used in taxonomical literature.

Linnaean taxonomy Rank based classification system for organisms

Linnaean taxonomy can mean either of two related concepts:

  1. the particular form of biological classification (taxonomy) set up by Carl Linnaeus, as set forth in his Systema Naturae (1735) and subsequent works. In the taxonomy of Linnaeus there are three kingdoms, divided into classes, and they, in turn, into lower ranks in a hierarchical order.
  2. a term for rank-based classification of organisms, in general. That is, taxonomy in the traditional sense of the word: rank-based scientific classification. This term is especially used as opposed to cladistic systematics, which groups organisms into clades. It is attributed to Linnaeus, although he neither invented the concept of ranked classification nor gave it its present form. In fact, it does not have an exact present form, as "Linnaean taxonomy" as such does not really exist: it is a collective (abstracting) term for what actually are several separate fields, which use similar approaches.
Phylogenetics Study of evolutionary relationships between organisms

In biology, phylogenetics is a part of systematics that addresses the inference of the evolutionary history and relationships among or within groups of organisms. These relationships are hypothesized by phylogenetic inference methods that evaluate observed heritable traits, such as DNA sequences, protein amino acid sequences, or morphology, often under a specified model of evolution of these traits. The result of such an analysis is a phylogeny —a diagrammatic hypothesis of relationships that reflects the evolutionary history of a group of organisms. The tips of a phylogenetic tree can be living taxa or fossils, and represent the 'end', or the present, in an evolutionary lineage. A phylogenetic diagram can be rooted or unrooted. A rooted tree diagram indicates the hypothetical common ancestor, or ancestral lineage, of the tree. An unrooted tree diagram makes no assumption about the ancestral line, and does not show the origin or "root" of the taxa in question or the direction of inferred evolutionary transformations. In addition to their proper use for inferring phylogenetic patterns among taxa, phylogenetic analyses are often employed to represent relationships among gene copies or individual organisms. Such uses have become central to understanding biodiversity, evolution, ecology, and genomes. In February 2021, scientists reported, for the first time, the sequencing of DNA from animal remains, a mammoth in this instance, over a million years old, the oldest DNA sequenced to date.

In biology, phenetics, also known as taximetrics, is an attempt to classify organisms based on overall similarity, usually in morphology or other observable traits, regardless of their phylogeny or evolutionary relation. It is closely related to numerical taxonomy which is concerned with the use of numerical methods for taxonomic classification. Many people contributed to the development of phenetics, but the most influential were Peter Sneath and Robert R. Sokal. Their books are still primary references for this sub-discipline, although now out of print.

Paraphyly Property of a group which includes only descendants of a common ancestor, but excludes at least one monophyletic subgroup

In taxonomy, a group is paraphyletic if it consists of the group's last common ancestor and all its descendants, but excluding a few—typically only one or two—monophyletic subgroups. The group is said to be paraphyletic with respect to the excluded subgroups. In contrast, a monophyletic group includes a common ancestor and all of its descendants. The terms are commonly used in phylogenetics and in the tree model of historical linguistics. Paraphyletic groups are identified by a combination of synapomorphies and symplesiomorphies. If many subgroups are missing from the named group, it is said to be polyparaphyletic.

Taxonomy (biology) Science of naming, defining and classifying organisms

In biology, taxonomy is the scientific study of naming, defining (circumscribing) and classifying groups of biological organisms based on shared characteristics. Organisms are grouped into taxa and these groups are given a taxonomic rank; groups of a given rank can be aggregated to form a more inclusive group of higher rank, thus creating a taxonomic hierarchy. The principal ranks in modern use are domain, kingdom, phylum, class, order, family, genus, and species. The Swedish botanist Carl Linnaeus is regarded as the founder of the current system of taxonomy, as he developed a ranked system known as Linnaean taxonomy for categorizing organisms and binominal nomenclature for naming organisms.

Zoology is the branch of biology that studies the animal kingdom, including the structure, embryology, evolution, classification, habits, and distribution of all animals, both living and extinct, and how they interact with their ecosystems. The term is derived from Ancient Greek ζῷον, zōion ('animal'), and λόγος, logos.

Cladogram Diagram used to show relations among groups of organisms with common origins

A cladogram is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to descendants, nor does it show how much they have changed, so many differing evolutionary trees can be consistent with the same cladogram. A cladogram uses lines that branch off in different directions ending at a clade, a group of organisms with a last common ancestor. There are many shapes of cladograms but they all have lines that branch off from other lines. The lines can be traced back to where they branch off. These branching off points represent a hypothetical ancestor which can be inferred to exhibit the traits shared among the terminal taxa above it. This hypothetical ancestor might then provide clues about the order of evolution of various features, adaptation, and other evolutionary narratives about ancestors. Although traditionally such cladograms were generated largely on the basis of morphological characters, DNA and RNA sequencing data and computational phylogenetics are now very commonly used in the generation of cladograms, either on their own or in combination with morphology.

Phylogenetic tree Branching diagram of evolutionary relationships between organisms

A phylogenetic tree is a branching diagram or a tree showing the evolutionary relationships among various biological species or other entities based upon similarities and differences in their physical or genetic characteristics. All life on Earth is part of a single phylogenetic tree, indicating common ancestry.

Molecular phylogenetics is the branch of phylogeny that analyzes genetic, hereditary molecular differences, predominately in DNA sequences, to gain information on an organism's evolutionary relationships. From these analyses, it is possible to determine the processes by which diversity among species has been achieved. The result of a molecular phylogenetic analysis is expressed in a phylogenetic tree. Molecular phylogenetics is one aspect of molecular systematics, a broader term that also includes the use of molecular data in taxonomy and biogeography.

Taxon Group of one or more populations of an organism or organisms which have distinguishing characteristics in common

In biology, a taxon is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular name and given a particular ranking, especially if and when it is accepted or becomes established. It is very common, however, for taxonomists to remain at odds over what belongs to a taxon and the criteria used for inclusion. If a taxon is given a formal scientific name, its use is then governed by one of the nomenclature codes specifying which scientific name is correct for a particular grouping.

Phylogenesis

Phylogenesis is the biological process by which a taxon appears. The science that studies these processes is called phylogenetics.

Evolutionary taxonomy, evolutionary systematics or Darwinian classification is a branch of biological classification that seeks to classify organisms using a combination of phylogenetic relationship, progenitor-descendant relationship, and degree of evolutionary change. This type of taxonomy may consider whole taxa rather than single species, so that groups of species can be inferred as giving rise to new groups. The concept found its most well-known form in the modern evolutionary synthesis of the early 1940s.

Outgroup (cladistics)

In cladistics or phylogenetics, an outgroup is a more distantly related group of organisms that serves as a reference group when determining the evolutionary relationships of the ingroup, the set of organisms under study, and is distinct from sociological outgroups. The outgroup is used as a point of comparison for the ingroup and specifically allows for the phylogeny to be rooted. Because the polarity (direction) of character change can be determined only on a rooted phylogeny, the choice of outgroup is essential for understanding the evolution of traits along a phylogeny.

Walter Max Zimmermann was a German botanist and systematist. Zimmernann’s notions of classifying life objectively based on phylogenetic methods and on evolutionarily important characters were foundational for modern phylogenetics. Though they were later implemented by Willi Hennig in his fundamental work on phylogenetic systematics, Zimmermann's contributions to this field have largely been overlooked. Zimmermann also made several significant developments in the field of plant systematics such as the discovery of the telome theory. The standard botanical author abbreviation W.Zimm. is applied to species he described.

In biology, a phylum is a level of classification or taxonomic rank below kingdom and above class. Traditionally, in botany the term division has been used instead of phylum, although the International Code of Nomenclature for algae, fungi, and plants accepts the terms as equivalent. Depending on definitions, the animal kingdom Animalia contains approximately 31 phyla; the plant kingdom Plantae contains about 14, and the fungus kingdom Fungi contains about 8 phyla. Current research in phylogenetics is uncovering the relationships between phyla, which are contained in larger clades, like Ecdysozoa and Embryophyta.

Caminalcules

Caminalcules are a fictive group of animal-like life forms, which were created as a tool for better understanding phylogenetics in real organisms. They were created by Joseph H. Camin and consist of 29 living 'species' and 48 fossil forms.

Alastair Culham is an English botanist. He is a member of the staff of the School of Biological Sciences at the University of Reading and Curator of the University of Reading Herbarium (RNG). He specialises in plant taxonomy, biosystematics and applications of techniques from molecular biology, phytogeography and phylogenetics. He focuses on broad-based research in biodiversity and taxonomy.

Outline of evolution Hierarchical outline list of articles related to evolution

The following outline is provided as an overview of and topical guide to evolution:

References

Notes

  1. 1 2 "Systematics: Meaning, Branches and Its Application". Biology Discussion. 2016-05-27. Retrieved 2017-04-12.
  2. Wilkins, J. S. What is systematics and what is taxonomy? Archived 2016-08-27 at the Wayback Machine . Available on http://evolvingthoughts.net
  3. Michener, Charles D., John O. Corliss, Richard S. Cowan, Peter H. Raven, Curtis W. Sabrosky, Donald S. Squires, and G. W. Wharton (1970). Systematics In Support of Biological Research. Division of Biology and Agriculture, National Research Council. Washington, D.C. 25 pp.
  4. Brusca, R. C., & Brusca, G. J. (2003). Invertebrates (2nd ed.). Sunderland, Mass. : Sinauer Associates, p. 27
  5. Fortey, Richard (2008), Dry Store Room No. 1: The Secret Life of the Natural History Museum, London: Harper Perennial, ISBN   978-0-00-720989-7
  6. Mayr, Ernst (1991). Principles of Systematic Zoology. New York: McGraw-Hill, p. 159.
  7. Mayr, Ernst (1991), p. 162.

Further reading