Race (biology)

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Four different ecotypes, i.e. ecological races, of the species Physcomitrella patens, stored at the International Moss Stock Center Ecotypes of Physcomitrella patens.JPG
Four different ecotypes, i.e. ecological races, of the species Physcomitrella patens , stored at the International Moss Stock Center

In biological taxonomy, race is an informal rank in the taxonomic hierarchy for which various definitions exist. Sometimes it is used to denote a level below that of subspecies, while at other times it is used as a synonym for subspecies. [1] It has been used as a higher rank than strain, with several strains making up one race. [2] [3] Races may be genetically distinct populations of individuals within the same species, [4] or they may be defined in other ways, e.g. geographically, or physiologically. [5] Genetic isolation between races is not complete, but genetic differences may have accumulated that are not (yet) sufficient to separate species. [6]

Contents

The term is recognized by some, but not governed by any of the formal codes of biological nomenclature. Taxonomic units below the level of subspecies are not typically applied to animals. [7]

Other terms

In botany, the Latin words stirps and proles were traditionally used, and proles was recommended in the first botanical Code of Nomenclature, published in 1868. [8]

Definitional approaches

Races are defined according to any identifiable characteristic, including gene frequencies. [9] "Race differences are relative, not absolute". [9] Adaptive differences that distinguish races can accumulate even with substantial gene flow and clinal (rather than discrete) habitat variation. [10] Hybrid zones between races are semi-permeable barriers to gene flow, [11] see for example the chromosome races of the Auckland tree wētā. [12]

Chromosomal race
A population distinguished by having a unique karyotypes, i.e., different chromosome numbers (ploidy), or different chromosome structure. [9]
Geographical race
A distinct population that is isolated in a particular area from other populations of a species, [13] and consistently distinguishable from the others, [13] e.g. morphology (or even only genetically [4] ). Geographic races are allopatric. [9]
Physiological race
A group of individuals that do not necessarily differ in morphology from other members of the species, but have identifiably different physiology or behaviour. [14] A physiological race may be an ecotype, part of a species that is adapted to a different local habitat, defined even by a specific food source. [15] Parasitic species, often tied to no geographic location, frequently have races that are adapted to different hosts, [14] [16] but difficult to distinguish chromosomally. [17]

In botany, where physiological race (mostly used in mycology [16] ), biological race, and biological form have been used synonymously, [14] [18] [19] a physiological race is essentially the same classification as a forma specialis , [14] except the latter is used as part of the infraspecific scientific name (and follows Latin-based scientific naming conventions), inserted after the interpolation "f. sp.", as in " Puccinia graminis f. sp. avenae"; while the name of a race is added after the binomial scientific name (and may be arbitrary, e.g. an alphanumeric code, usually with the word "race"): " Podosphaera xanthii race S". [17]

A physiological race is not to be confused with a physiologic race, an obsolete term for cryptic species. [16] Neither biological form nor forma specialis should be confused with the formal botanical taxonomic rank of forma or form, or with the zoological term form, an informal description (often seasonal) which is not taxonomic.

The term race has also historically been used in relation to domesticated animals, as another term for breed ; [4] this usage survives in combining form, in the term landrace, also applied to domesticated plants. The cognate words for race in many languages (Spanish: raza; German: Rasse; French: race) may convey meanings the English word does not, and are frequently used in the sense of 'domestic breed'. [20]

Distinguishing from other taxonomic ranks

If the races are sufficiently different or if they have been tested to show little genetic connection regardless of phenotype, two or more groups/races can be identified as subspecies or (in botany, mycology, and phycology) another infraspecific rank), and given a name. Ernst Mayr wrote that a subspecies can be "a geographic race that is sufficiently different taxonomically to be worthy of a separate name." [21] [22]

Study of populations preliminarily labelled races may sometimes lead to classification of a new species. For example, in 2008, two populations of the brown planthopper (Nilaparvata lugens) in the Philippines, one adapted to feeding on rice, and another on Leersia hexandra grass, were reclassified from races into "two distinct, but very closely allied, sympatric species", based on poor survival rate when given the opposite food source, barriers to hybridization between the populations, uniform preference for mating between members of the same population, differences in mating sounds, oviposition variances, and other distinguishable characteristics. [15]

For pathogenic bacteria adapted to particular hosts, races can be formally named as pathovars. For parasitic organisms governed by the International Code of Nomenclature for algae, fungi, and plants , the term forma specialis (plural formae speciales) is used.

In mycology and phytopathology

Classification of fungal microbes into races is done frequently in mycology, the study of fungi, and especially in phytopathology, the study of plant diseases, which are often fungal. The term "physiologic race" was recommended for use over "biologic form" at the International Botanical Congress of 1935. Although historically the term has been used inconsistently by plant pathologists, the modern trend is to use race to refer to "groups of host genotypes permitting characterization of virulence" [23] (in simpler terms: grouping the parasitic fungi into races based on how strongly they affect particular host plants).

Commercial Cucumis melo (cantaloupe and muskmelon) production, for example, has been engaged in a biological "arms race", since 1925, against cucurbit powdery mildew, caused by successively arising races of Podosphaera xanthii fungus, with new cultivars of melons being developed for resistance to these pathogens. [17] [24]

A 2004 literature review of this issue concluded that "race identification is important for basic research and is especially important for the commercial seed industry", but was seen as having little utility in horticulture for choosing specific cultivars, because of the rapidity with which the local pathogen population can change geographically, seasonally, and by host plant. [17]

Classification of fungal races can be difficult because host plants' responses to particular populations of fungi can be affected by humidity, light, temperature, and other environmental factors; different host plants may not all respond to particular fungal populations or vice versa; and identification of genetic differences between populations thought to form distinct fungal races can be elusive. [17]

See also

Related Research Articles

Outline of biology Outline of subdisciplines within biology

Biology – The natural science that studies life. Areas of focus include structure, function, growth, origin, evolution, distribution, and taxonomy.

Ploidy Number of sets of chromosomes in a cell

Ploidy is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Sets of chromosomes refer to the number of maternal and paternal chromosome copies, respectively, in each homologous chromosome pair, which chromosomes naturally exist as. Somatic cells, tissues, and individual organisms can be described according to the number of sets of chromosomes present : monoploid, diploid, triploid, tetraploid, pentaploid, hexaploid, heptaploid or septaploid, etc. The generic term polyploid is often used to describe cells with three or more chromosome sets.

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.

Hybrid (biology) Offspring of cross-species reproduction

In biology, a hybrid is the offspring resulting from combining the qualities of two organisms of different breeds, varieties, species or genera through sexual reproduction. Hybrids are not always intermediates between their parents, but can show hybrid vigor, sometimes growing larger or taller than either parent. The concept of a hybrid is interpreted differently in animal and plant breeding, where there is interest in the individual parentage. In genetics, attention is focused on the numbers of chromosomes. In taxonomy, a key question is how closely related the parent species are.

Ascomycota Division or phylum of fungi

Ascomycota is a phylum of the kingdom Fungi that, together with the Basidiomycota, forms the subkingdom Dikarya. Its members are commonly known as the sac fungi or ascomycetes. It is the largest phylum of Fungi, with over 64,000 species. The defining feature of this fungal group is the "ascus", a microscopic sexual structure in which nonmotile spores, called ascospores, are formed. However, some species of the Ascomycota are asexual, meaning that they do not have a sexual cycle and thus do not form asci or ascospores. Familiar examples of sac fungi include morels, truffles, brewers' and bakers' yeast, dead man's fingers, and cup fungi. The fungal symbionts in the majority of lichens such as Cladonia belong to the Ascomycota.

The gene pool is the set of all genes, or genetic information, in any population, usually of a particular species.

Subspecies Taxonomic rank subordinate to species

In biological classification, the term subspecies refers to one of two or more populations of a species living in different subdivisions of the species' range and varying from one another by morphological characteristics. A single subspecies cannot be recognized independently: a species is either recognized as having no subspecies at all or at least two, including any that are extinct. The term may be abbreviated to subsp. or ssp. The plural is the same as the singular: subspecies.

Within biological taxonomy, a honey bee race would be an informal rank in the taxonomic hierarchy, below the level of subspecies. It has been used as a higher rank than strain, with several strains making up one race. Therefore, a strain is a lower-level taxonomic rank used at the intraspecific level within a race of a subspecies. Strains are often seen as inherently artificial concepts, more usually within biology as characterized by a specific intent for genetic isolation, however, within beekeeping circles, strain is more likely to be used to describe very minor differences throughout the same subspecies, such as the color ranges of A. m. carnica from brown to grey. Within A. m. ligustica there are two races, the darker leather brown northern Italian bee from the Ligurian Alps region which was discovered to be resistant to acarine in the 1900s, while the other Italian bee race, from regions near Bologna and further south, was highly susceptible to acarine and within this race there are two color strains, the traditional Italian yellow and a rarer all-golden color.

Powdery mildew Fungal plant disease

Powdery mildew is a fungal disease that affects a wide range of plants. Powdery mildew diseases are caused by many different species of fungi in the order Erysiphales. Powdery mildew is one of the easier plant diseases to identify, as its symptoms are quite distinctive. Infected plants display white powdery spots on the leaves and stems. The lower leaves are the most affected, but the mildew can appear on any above-ground part of the plant. As the disease progresses, the spots get larger and denser as large numbers of asexual spores are formed, and the mildew may spread up and down the length of the plant.

Arbuscular mycorrhiza Symbiotic penetrative association between a fungus and the roots of a vascular plant

An arbuscular mycorrhiza (AM) is a type of mycorrhiza in which the symbiont fungus penetrates the cortical cells of the roots of a vascular plant forming arbuscules.

Conidium Asexual, non-motile spore of a fungus

A conidium (pl. conidia), sometimes termed an asexual chlamydospore or chlamydoconidium (pl. chlamydoconidia), is an asexual, non-motile spore of a fungus. The word conidium comes from the Ancient Greek word for dust, κόνις (kónis). They are also called mitospores due to the way they are generated through the cellular process of mitosis. The two new haploid cells are genetically identical to the haploid parent, and can develop into new organisms if conditions are favorable, and serve in biological dispersal.

Biopesticides, a contraction of 'biological pesticides', include several types of pest management intervention: through predatory, parasitic, or chemical relationships. The term has been associated historically with biological pest control – and by implication, the manipulation of living organisms. Regulatory positions can be influenced by public perceptions, thus:

Species complex Group of closely related similar organisms

In biology, a species complex is a group of closely related organisms that are so similar in appearance that the boundaries between them are often unclear. Terms that are sometimes used synonymously but have more precise meanings are cryptic species for two or more species hidden under one species name, sibling species for two cryptic species that are each other's closest relative, and species flock for a group of closely related species that live in the same habitat. As informal taxonomic ranks, species group, species aggregate, macrospecies, and superspecies are also in use.

Forma specialis, abbreviated f. sp. without italics, is an informal taxonomic grouping allowed by the International Code of Nomenclature for algae, fungi, and plants, that is applied to a parasite which is adapted to a specific host. This classification may be applied by authors who do not feel that a subspecies or variety name is appropriate, and it is therefore not necessary to specify morphological differences that distinguish this form. The literal meaning of the term is 'special form', but this grouping does not correspond to the more formal botanical use of the taxonomic rank of forma or form.

<i>Zymoseptoria tritici</i> Species of fungus

Zymoseptoria tritici, synonyms Septoria tritici, Mycosphaerella graminicola, is a species of filamentous fungus, an ascomycete in the family Mycosphaerellaceae. It is a wheat plant pathogen causing septoria leaf blotch that is difficult to control due to resistance to multiple fungicides. The pathogen today causes one of the most important diseases of wheat.

<i>Podosphaera fuliginea</i> Species of fungus

Podosphaera fuliginea is a plant pathogen that causes powdery mildew on cucurbits. Podosphaera fuliginea and Erysiphe cichoracearum are the two most commonly recorded fungi causing cucurbit powdery mildew. In the past, Erysiphe cichoracearum was considered to be the primary causal organism throughout most of the world. Today, Podosphaera fuliginea is more commonly reported.

Fungus Biological kingdom, separate from plants and animals

A fungus is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from the other eukaryotic kingdoms, which by one traditional classification include Plantae, Animalia, Protozoa, and Chromista.

This glossary of biology terms is a list of definitions of fundamental terms and concepts used in biology, the study of life and of living organisms. It is intended as introductory material for novices; for more specific and technical definitions from sub-disciplines and related fields, see Glossary of genetics, Glossary of evolutionary biology, Glossary of ecology, and Glossary of scientific naming, or any of the organism-specific glossaries in Category:Glossaries of biology.

Ectomycorrhiza Non-penetrative symbiotic association between a fungus and the roots of a vascular plant

An ectomycorrhiza is a form of symbiotic relationship that occurs between a fungal symbiont, or mycobiont, and the roots of various plant species. The mycobiont is often from the phyla Basidiomycota and Ascomycota, and more rarely from the Zygomycota. Ectomycorrhizas form on the roots of around 2% of plant species, usually woody plants, including species from the birch, dipterocarp, myrtle, beech, willow, pine and rose families. Research on ectomycorrhizas is increasingly important in areas such as ecosystem management and restoration, forestry and agriculture.

Zoophthora is a genus of fungi in the family Entomophthoraceae. Like other taxa in this family, Zoophthora species cause disease in insects and as such are considered entomopathogenic fungi.

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