Race (biology)

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This article is about the biological taxonomy term. For the sociological concept, see Race and society. For the anthropological term, see Race (human classification). For the RACE technique in molecular biology, see Rapid amplification of cDNA ends.
Four different ecotypes, i.e. ecological races, of the species Physcomitrella patens, stored at the International Moss Stock Center

In biological taxonomy, a race is an informal rank (not governed by the codes of nomenclature), below the level of subspecies in the formal taxonomic hierarchy. It has been used as a higher rank than strain, with several strains making up one race.[1][2] Various definitions exist. Races may be distinct phenotypic populations within the same species, or they may be defined in other ways.[3] Genetic isolation between races is not complete, but genetic differences may have accumulated that are not (yet) sufficient to separate species.[4]

Definitional approaches[edit]

Races are defined according to any identifiable characteristic, including gene frequencies.[5] "Race differences are relative, not absolute".[5] Adaptive differences that distinguish races can accumulate even with substantial gene flow and clinal (rather than discrete) habitat variation.[6]

  • A physiological race, or forma specialis in botany, is a group of individuals that do not necessarily differ in morphology from other members of the species, but have identifiably different physiology or habits.[7] Parasitic species frequently have races that are adapted to different hosts.[7]
  • An ecological race is an ecotype, part of a species that is adapted to a different local habitat. A race may be defined even by a specific food source[8] or host organism.[9]
  • A chromosomal race is distinguished by having a unique karyotypes, i.e., different chromosome numbers (ploidy), or different chromosome structure.[5]

The term has also been used in relation to domesticated animals and plants;[3] this usage survives in combining form, in the term landrace.

Distinguishing from other taxonomic ranks[edit]

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."[10][11]

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.[8]

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, formae speciales are used.

In mycology and phytopathology[edit]

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".[12]

Commercial Cucumis melo (cantaloup 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.[9][13]

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.[9]

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.[9]

See also[edit]

References[edit]

  1. ^ Gotoh, T.; Bruin, J.; Sabelis, M. W.; Menken, S. B. J. (1993). "Host race formation in Tetranychus urticae: Genetic differentiation, host plant preference, and mate choice in a tomato and a cucumber strain". Entomologia Experimentalis et Applicata 68 (2): 171–178. doi:10.1111/j.1570-7458.1993.tb01700.x. 
  2. ^ Ritchie, D.F.; Dittapongpitch, V. (1991), "Copper- and Streptomycin-Resistant Strains and Host Differentiated Races of Xanthomonas campestris pv. vesicatoria in North Carolina" (PDF), Plant Disease 75 (7): 733–736 
  3. ^ a b c Walker, P. M. B., ed. (1988). "Race". The Wordsworth Dictionary of Science and Technology. W. R. Chambers Ltd. and Cambridge University Press. 
  4. ^ Jaenike, J. (1981), "Criteria for Ascertaining the Existence of Host Races", The American Naturalist 117 (5): 830–834, doi:10.2307/2460772, JSTOR 2460772 
  5. ^ a b c d Rieger, R.; Michaelis, A.; Green, M.M. (1968). A glossary of genetics and cytogenetics: Classical and molecular. New York: Springer-Verlag. ISBN 9780387076683. 
  6. ^ Van Buskirk, J. (2014), "Incipient habitat race formation in an amphibian", Journal of Evolutionary Biology 27 (3): 585–592, doi:10.1111/jeb.12327 
  7. ^ a b Walker, P.M.B., ed. (1988). "Entry for Physiological Race". The Wordsworth Dictionary of Science and Technology. W. R. Chambers Ltd. and Cambridge University Press. 
  8. ^ a b Claridge, M. F.; Den Hollander, J.; Morgan, J. C. (May 1985). "The status of weed-associated populations of the brown planthopper, Nilaparvata lugens (Stål) – host race or biological species?". Zoological Journal of the Linnean Society 84 (1): 77–90. Retrieved 1 August 2015. 
  9. ^ a b c d Cohen, R.; Burger, Y.; Katzir, N. (2004). "Monitoring Physiological races of Podosphaera xanthii (syn. Sphaerotheca fuliginea), the Causal Agent of Powdery Mildew in Curcubits: Factors Affecting Race Identification and the Importance for Research and Commerce". Phythoparasitica 32 (2): 174–183. Retrieved 10 August 2015. 
  10. ^ Mayr, Ernst (1970). Populations, Species, and Evolution. Cambridge, Massachusetts: Belknap / Harvard University Press. ISBN 0-674-69013-3.  An Abridgment and revision of Animal Species and Evolution (1963).
  11. ^ Mayr, Ernst (Winter 2002). "The Biology of Race and the Concept of Equality". Daedalus: 89–94. 
  12. ^ Kirk PM, Cannon PF, Minter DW, Stalpers JA. (2008). Dictionary of the Fungi (10th ed.). Wallingford, UK: CAB International. p. 534. ISBN 978-0-85199-826-8. 
  13. ^ McCreight, James D.; Coffey, Michael D. (June 2011). "Inheritance of Resistance in Melon PI 313970 to Cucurbit Powdery Mildew Incited by Podosphaera xanthii Race S". HortScience 46 (6): 838–840. Retrieved 10 August 2015.