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Ecotype

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Not to be confused withEcophenotypeorSubspecies.
Four differentecotypesofPhyscomitrella patens,stored at theInternational Moss Stock Center

Inevolutionary ecology,anecotype,[note 1]sometimes calledecospecies,describes a genetically distinct geographic variety,population,orracewithin aspecies,which is genotypicallyadaptedto specific environmental conditions.

Typically, though ecotypes exhibitphenotypicdifferences (such as inmorphologyorphysiology) stemming fromenvironmental heterogeneity,they are capable of interbreeding with other geographically adjacent ecotypes without loss of fertility or vigor.[1][2][3][4][5]

Definition[edit]

An ecotype is a variant in which thephenotypicdifferences are too few or too subtle to warrant being classified as a subspecies. These different variants can occur in the same geographic region where distinct habitats such as meadow, forest, swamp, and sand dunes provide ecological niches. Where similar ecological conditions occur in widely separated places, it is possible for a similar ecotype to occur in the separated locations. An ecotype is different from a subspecies, which may exist across a number of different habitats. In animals, ecotypes owe their differing characteristics to the effects of a very local environment.[6]Therefore, ecotypes have notaxonomic rank.

Terminology[edit]

Ecotypes are closely related tomorphs.In the context ofevolutionary biology,genetic polymorphismis the occurrence in the equilibrium of two or more distinctly different phenotypes within a population of a species, in other words, the occurrence of more than oneformormorph.The frequency of these discontinuous forms (even that of the rarest) is too high to be explained bymutation.In order to be classified as such, morphs must occupy the same habitat at the same time and belong to apanmicticpopulation (whose members can all potentially interbreed). Polymorphism is actively and steadily maintained in populations of species by natural selection (most famouslysexual dimorphismin humans) in contrast totransient polymorphismswhere conditions in a habitat change in such a way that a "form" is being replaced completely by another.

In fact, Begon, Townsend, and Harper assert that

There is not always clear distinction between local ecotypes and genetic polymorphisms.

The notions "form" and "ecotype" may appear to correspond to a static phenomenon, however; this is not always the case. Evolution occurs continuously both in time and space, so that two ecotypes or forms may qualify as distinct species in only a few generations. Begon, Townsend, and Harper use an illuminating analogy on this:

... the origin of a species, whetherallopatricorsympatric,is a process, not an event. For the formation of a new species, like the boiling of an egg, there is some freedom to argue about when it is completed.

Thus ecotypes and morphs can be thought of as precursory steps of potentialspeciation.[7]

Range and distribution[edit]

Panicum virgatumecotypes and their distribution inNorth America

Experiments indicate that sometimes ecotypes manifest only when separated by great spatial distances (of the order of 1,000 km). This is due tohybridizationwhereby different but adjacent varieties of the same species (or generally of the sametaxonomic rank) interbreed, thus overcoming local selection. However other studies reveal that the opposite may happen, i.e., ecotypes revealing at very small scales (of the order of 10 m), within populations, and despite hybridization.[1]

In ecotypes, it is common for continuous, gradual geographic variation to impose analogous phenotypic and genetic variation.[1]This situation is calledcline.A well-known example of a cline is the skin color gradation in indigenous human populations worldwide, which is related to latitude and amounts of sunlight.[8]But often the distribution of ecotypes isbimodalor multimodal. This means that ecotypes may display two or more distinct and discontinuous phenotypes even within the same population. Such phenomenon may lead tospeciationand can occur if conditions in a local environment change dramatically through space or time.[1]

Examples[edit]

Rangifer tarandus caribou,a member of the woodland ecotype
  • Tundrareindeer and woodland reindeer are two ecotypes ofreindeer.The first migrate (travelling 5,000 km) annually between the two environments in large numbers whereas the other (who are much fewer) remain in the forest for the summer.[9]In North America, the speciesRangifer tarandus(locally known as caribou),[10][11]was subdivided into five subspecies[note 2]by Banfield in 1961.[12]Caribou are classified by ecotype depending on several behavioural factors – predominant habitat use (northern, tundra, mountain, forest, boreal forest, forest-dwelling), spacing (dispersed or aggregated) and migration (sedentary or migratory).[13][14][15]For example, the subspeciesRangifer tarandus caribouis further distinguished by a number of ecotypes, includingboreal woodland caribou,mountain woodland caribou, andmigratory woodland caribou(such as the migratory George River Caribou Herd in the Ungava region of Quebec).
  • Arabis fecunda,a herbendemicto somecalcareoussoils of Montana, United States, can be divided into two ecotypes. The one "low elevation" group lives near the ground in an arid, warm environment and has thus developed a significantly greater tolerance against drought than the "high elevation" group. The two ecotypes are separated by a horizontal distance of about 100 km (62 mi).[1]
  • It is commonly accepted that theTucuxidolphin has two ecotypes – the riverine ecotype found in some South American rivers and the pelagic ecotype found in the South Atlantic Ocean.[16]In 2022, thecommon bottlenose dolphin(Tursiops truncatus), which had been considered to have two ecotypes in the western North Atlantic, was separated into two species by Costa et al.[17]based on morphometric and genetic data, with the near-shore ecotype becomingTursiops erebennusCope, 1865,described in the nineteenth century from a specimen collected in the Delaware River.
  • Thewarbler finchand theCocos Island finchare viewed as separate ecotypes.[18]
  • TheScots pine(Pinus sylvestris) has 20 different ecotypes in an area from Scotland to Siberia, all capable of interbreeding.[19]
  • Ecotype distinctions can be subtle and do not always require large distances; it has been observed that two populations of the sameHelixsnail species separated by only a few hundred kilometers prefer not to cross-mate, i.e., they reject one another as mates. This event probably occurs during the process of courtship, which may last for hours.[citation needed]

See also[edit]

Explanatory notes[edit]

  1. ^Greek:οίκος= home andτύπος= type, coined byGöte Turessonin 1922
  2. ^Banfield, who worked with both theCanadian Wildlife Serviceand theNational Museum of Canada,in his often-cited 1961 classification, identified five subspecies ofRangifer tarandus:1) the largely migratorybarren-ground caribousubspeciesRangifer tarandus groenlandicus,which are found mainly in theCanadianterritories ofNunavutand the Northwest Territories, along with westernGreenland;2) the subspeciesRangifer tarandus caribouwhich is divided into ecotypes:boreal woodland caribou,(also known as forest-dwelling, woodland caribou (boreal), mountain woodland caribou andmigratory woodland caribou) —the migratory George River Caribou Herd, for example in the Ungava region of Quebec; 3) Rangifer tarandus pearyi (Peary caribou), the smallest of the species, known as Tuktu in Inuktitut, found in the northern islands ofNunavutand the Northwest Territories; 4)Rangifer tarandus grantisubspeciesGrant’s caribou,which are mainly migratory and live in Alaska and the northern Yukon and 5) theR. t. dawsonisubspecies; †Queen Charlotte Islands cariboufrom theQueen Charlotte Islands(extinct since 1910)

References[edit]

  1. ^abcdeEcology: From individuals to ecosystemsby Begon, Townsend, Harper, Blackwell Publishing 4th ed. (2006), p.5,6,7,8
  2. ^Turesson, Göte (9 July 2010). "The Genotypical Response of the Plant Species to the Habitat".Hereditas.3(3): 211–350.doi:10.1111/j.1601-5223.1922.tb02734.x.hdl:2027/uc1.b2636816.
  3. ^Molles, Manuel C. Jr. (2005).Ecology: Concepts and Applications(3rd ed.). New York: The McGraw-Hill Companies, Inc. pp.201.ISBN978-0-07-243969-4.
  4. ^Environmental Encyclopediaby Bortman, Brimblecombe, Mary Ann Cunningham, William P. Cunningham, Freedman - 3rd ed., p.435, "Ecotype"
  5. ^"ecotype - Dictionary of botany".botanydictionary.org.
  6. ^Ernst Mayr (1999)."VIII-Nongeographic speciation".Systematics and the Origin of Species, from the Viewpoint of a Zoologist.Harvard University Press. pp. 194–195.ISBN9780674862500.
  7. ^Lowry, David B. (June 2012)."Ecotypes and the controversy over stages in the formation of new species".Biological Journal of the Linnean Society.106(2): 241–257.doi:10.1111/j.1095-8312.2012.01867.x.
  8. ^"Race". (2009).Encyclopædia Britannica.Ultimate Reference Suite. Chicago: Encyclopædia Britannica.
  9. ^"reindeer (Rangifer tarandus)" Encyclopædia Britannica. Ultimate Reference Suite. Chicago: Encyclopædia Britannica, 2009
  10. ^"Designatable Units for Caribou (Rangifer tarandus) in Canada"(PDF),COSEWIC,Ottawa, Ontario: Committee on the Status of Endangered Wildlife in Canada, p. 88, 2011, archived fromthe original(PDF)on 3 March 2016,retrieved18 December2013
  11. ^COSEWIC 2011:3.
  12. ^Banfield, Alexander William Francis (1961), "A Revision of the Reindeer and Caribou, Genus Rangifer",Bulletin,Biological Services,177(66),National Museum of Canada,OCLC4636472
  13. ^Bergerud, A.T. (1 January 1996)."Evolving perspectives on caribou population dynamics, have we got it right yet?".Rangifer.16(4): 95.doi:10.7557/2.16.4.1225.
  14. ^Festa-Bianchet, M.; Ray, J.C.; Boutin, S.; Côté, S.D.; Gunn, A. (May 2011)."Conservation of caribou ( Rangifer tarandus ) in Canada: an uncertain future".Canadian Journal of Zoology.89(5): 419–434.doi:10.1139/z11-025.
  15. ^Mager, Karen H. (2012).Population Structure And Hybridization Of Alaskan Caribou And Reindeer: Integrating Genetics And Local Knowledge(Thesis).CiteSeerX10.1.1.692.2993.hdl:11122/9130.
  16. ^Cunha, H.A.; da Silva, V.M.F.; Lailson-Brito, J; Santos, M.C.O.; Flores, P.A.C.; Martin, A.R.; Azevedo, A.F.; Fragoso, A.B.L.; Zanelatto, R.C.; Solé-Cava, A.M. (December 2005). "Riverine and marine ecotypes of Sotalia dolphins are different species".Marine Biology.148(2): 449–457.doi:10.1007/s00227-005-0078-2.S2CID49359327.
  17. ^Costa, A.P.B.; Mcfee, W.; Wilcox, L.A.; Archer, F.I.; Rosel, P.E. (2022)."The common bottlenose dolphin (Tursiops truncatus) ecotypes of the western North Atlantic revisited: an integrative taxonomic investigation supports the presence of distinct species ".Zoological Journal of the Linnean Society.196(4): 1608–1636.doi:10.1093/zoolinnean/zlac025.
  18. ^Hau, Michaela; Wikelski, Martin (19 April 2001). "Darwin's Finches".Encyclopedia of Life Sciences.doi:10.1038/npg.els.0001791.ISBN978-0-470-01617-6.
  19. ^Introduction to Ecology (1983),J.C. Emberlin, chapter 8
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