Ecotype

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In evolutionary biology and ecology, an ecotype (Greek: οίκος = home and τύπος = type) is a term (coined by Göte Turesson in 1922^[1][2]) used to describe a genetically distinct geographic variety, population or race within species (or among closely related), which is adapted to specific environmental conditions such as local selective pressure or physical isolation.^[3][4]

Typical properties of ecotypes

• Exhibition of phenotypic differences (such as in morphology or physiology) stemming from environmental heterogeneity^[5]
• Capability of interbreeding with other geographically adjacent ecotypes without loss of fertility or vigor^[6]

Range

Experiments indicate that sometimes ecotypes manifest only if separated by great spatial distances (of the order of 1000 km). This is due to a process called hybridization whereby different but spatially adjacent varieties of the same species (or generally of the same taxonomic rank) interbreed. In this case geographic differences fade with small distances as hybridization overcomes local selection.^[7] However other studies reveal that the opposite may happen, i.e. ecotypes showing at the very small scales (of the order of 10 m), within populations and despite hybridization.^[8]

Distribution

In ecotypes, it is common for gradual or continuous geographic variation to impose analogous phenotypic and/or genetic variation.^[9] This situation is called cline. A well-known example of cline is the skin color gradation in indigenous human populations worldwide, which is related to latitude and amounts of sunlight.^[10] But often the distribution of ecotypes is bimodal or multimodal. This means that ecotypes may display two or more distinct and discontinuous phenotypes even within the same population. Such a case can occur if for example conditions in a local environment change dramatically through space or time.^[11][12]

Contents 1 Examples 2 Terminology and controversy 3 See also 4 References

[edit] Examples

1. Tundra reindeer and forest (or woodland) reindeer are two ecotypes of reindeer. The first migrate (travelling 5000 km) annually between the two environments in large numbers whereas the other (who are much fewer) remain in the forest for the summer.^[13] Currently, and since 1961 classification, tundra reindeer comprise five subspecies and woodland reindeer two.^[14]

2. Another species, Arabis fecunda, a herb that grows only in some calcareous soils in Montana, USA, can be divided into two ecotypes. The one "low elevetion" group lives near the ground in an arid, warm environment and has thus developed a significantly greater tolerance against drought than the "high eleveation" group. The two ecotypes are separated by a distance of about 100 km. ^[15]

3. It is commonly accepted that the Tucuxi dolphin has two ecotypes - the riverine ecotype found in some South American rivers and the pelagic ecotype found in the South Atlantic Ocean.^{[citation needed]}Similarly, it is accepted that the Common Bottlenose Dolphin has two ecotypes in the Western North Atlantic.^[16]

4. The Warbler finch and the Cocos Island Finch are viewed as separate ecotypes.^[17]

[edit] Terminology and controversy

Ecotypes have no main taxonomic rank in modern biological classification. However, in "Environmental Encyclopedia", 2003, by Bortman, Brimblecombe, Mary Ann Cunningham, William P. Cunningham, and Freedman, they are said to be "taxonomically equivalent to subspecies". This is true in the sense that ecotypes can be classified sometimes as subspecies and the opposite. So as generic terms, ecotypes and subspecies are roughly on the same step of most classification attempts. Yet the above definition of ecotype may cause some confusion with other terms. Such misunderstanding in evolutionary biology is common. In fact in "Ecology - From individuals to ecosystems", Begon, Townsend and Harper assert that

"There is not always clear distinction between local ecotypes and genetic polymorphisms" ^[18]

The definition of polymorphism:

"(Genetic) polymorphism in the context of evolutionary biology is the occurrence in equilibrium of two or more distinctly different phenotypes within a population of a species, in other words, the occurrence of more than one form or morph. The frequency of these discontinuous forms (even that of the rarest) is too high to be explained by mutation. In order to be classified as such, morphs must occupy the same habitat at the same time and belong to a panmictic population (whose all members can potentially interbreed). Polymorphism is actively and steadily maintained in populations of species by natural selection (most famously sexual dimorphism in humans) in contrast to transient polymorphisms where conditions in a habitat change in such a way that a "form" is being replaced completely by another."

Thus a morph is merely a refinement or a specification of an ecotype.

Wikipedia contains the term form in three different biology-related articles:

• Form (botany)
• Form (zoology)
• Polymorphism (biology)

Even the very meaning of species, the basic unit of biological classification has not yet been resolved. See species problem and ring species.

However such controversy is partly justified from the observed enormous perplexity of nature (see biodiversity). Another part is due to nomenclature and linguistic issues.

The above definition of ecotype may communicate a sense of discrete phenomenon. But what it intends to describe is truly a fluctuating, continuous and perpetual process. For example with current terminology, the two raindeer ecotypes may be eligible to be classified as different species in only a few generations. Begon, Townsend and Harper use an illuminating analogy:

"This reminds us, too, that the origin of a species, whether allopatric or sympatric, 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." ^[19]

Hence evolutionary biology requires a degree of open-mindness when confronting such disturbances in terminology, because at the end of the line, ecotypes, morphs, species, subspecies and their mechanisms all intend to describe aspects of the same thing: evolution by natural selection and variation in the natural world. It is just that the rules and their exceptions may change with time and circumstance, so several formulations may apply simultaneously.

Another comparison pertaining to the above notions could be Wikipedia itself. Wikipedia is an endeavour to openly accumulate all human knowledge and understanding. As a natural result, it's an ever-evolving, ever-updating and ever-improving process. But it can never be designated "at perfect level" (see also fitness) since for instance new information will always emerge. This "flaw" often arouses controversy and debate.

Particularly in science, most controversy is generated and justified by the observation of certain paradoxes or extraordinary situations . In biology for example, the paradox of the plankton contradicts the competitive exclusion principle. Light is both a particle and a wave (Wave-particle duality). Ring species is a very unusual and bewildering circumstance. See also: List of paradoxes. Hopefully, as confirmed human knowledge expands and deepens such contradictions will be solved or better understood.

[edit] See also

• Species
• Speciation
• Subspecies
• Polymorphism (biology)
• Ecological niche
• Cline (biology)
• Ecotone
• Species problem
• Ring species
• Common descent
• Taxonomic rank
• Biological classification
• Taxon
• Transplant experiment

[edit] References

1. ^ Begon, Townsend, Harper - Ecology: From individuals to ecosystems , Blackwell Publishing, 4th ed. (2006), p.5
2. ^ Turesson, Turesson G. (1992). The genotypical response of the plant species to the habitat.. Hereditas 3. pp. 211-350. 
3. ^ Environmental Encyclopedia by Bortman, Brimblecombe, Mary Ann Cunningham, William P. Cunningham, Freedman - 3rd ed., p.435, "Ecotype"
4. ^ Molles, Manuel C., Jr. (2005). Ecology: Concepts and Applications (3rd edition ed.). New York: The McGraw-Hill Companies, Inc.. pp. 201. ISBN 0-07-243969-6. 
5. ^ Environmental Encyclopedia by Bortman, Brimblecombe, Mary Ann Cunningham, William P. Cunningham, Freedman - 3rd ed., p.435, "Ecotype"
6. ^ Environmental Encyclopedia by Bortman, Brimblecombe, Mary Ann Cunningham, William P. Cunningham, Freedman - 3rd ed., p.435, "Ecotype"
7. ^ Begon, Townsend, Harper - Ecology: From individuals to ecosystems , Blackwell Publishing, 4th ed. (2006), p. 6
8. ^ Begon, Townsend, Harper - Ecology: From individuals to ecosystems , Blackwell Publishing, 4th ed. (2006), p. 7,8
9. ^ Begon, Townsend, Harper - Ecology: From individuals to ecosystems , Blackwell Publishing, 4th ed. (2006), p. 7,8
10. ^ race. (2009). Encyclopædia Britannica. Ultimate Reference Suite. Chicago: Encyclopædia Britannica.
11. ^ Environmental Encyclopedia by Bortman, Brimblecombe, Mary Ann Cunningham, William P. Cunningham, Freedman - 3rd ed., p.435, "Ecotype"
12. ^ Begon, Townsend, Harper - Ecology: From individuals to ecosystems , Blackwell Publishing, 4th ed. (2006), p.5
13. ^ "reindeer (Rangifer tarandus)" Encyclopædia Britannica. Ultimate Reference Suite. Chicago: Encyclopædia Britannica, 2009
14. ^ Reindeer
15. ^ Begon, Townsend, Harper (2006). Ecology: From individuals to ecosystems (4th ed.). Blackwell Publishing. 
16. ^ Common Bottlenose Dolphin
17. ^ Encyclopedia of life sciences, 2007, John Wiley & Sons, "Darwin’s Finches"
18. ^ Begon, Townsend, Harper - Ecology: From individuals to ecosystems , Blackwell Publishing, 4th ed. (2006), p. 7
19. ^ Begon, Townsend, Harper - Ecology: From individuals to ecosystems , Blackwell Publishing, 4th ed. (2006), p. 10