ecotype

In evolutionary ecology, an ecotype (Greek: οίκος = home and τύπος = type, coined by Göte Turesson in 1922^[1][2]) describes a genetically distinct geographic variety, population or race within species (or among closely related), which is adapted to specific environmental conditions.^[3][4] Typically, ecotypes exhibit phenotypic differences (such as in morphology or physiology) stemming form environmental heterogeneity^[5] and are capable of interbreeding with other geographically adjacent ecotypes without loss of fertility or vigor.^[6]

Range and Distribution

Experiments indicate that sometimes ecotypes manifest only if separated by great spatial distances (of the order of 1000 km). This is due to hybridization whereby different but adjacent varieties of the same species (or generally of the same taxonomic rank) interbreed, thus overcoming 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]

In ecotypes, it is common for continuous, gradual 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 phenomenon may lead to speciation and can occur if conditions in a local environment change dramatically through space or time.^[11][12]

Examples

Rangifer tarandus caribou, a subspecies of the woodland ecotype.

Arabis fecunda in Montana.

• 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]

• Arabis fecunda, a herb endemic to some calcareous soils of Montana, USA, 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.^[15]

• 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.^[16]Similarly, it is accepted that the Common Bottlenose Dolphin has two ecotypes in the Western North Atlantic.^[17]

• The Warbler finch and the Cocos Island Finch are viewed as separate ecotypes.^[18]

• The Scots Pine (Pinus sylvestris) has 20 different ecotypes in an area from Scotland to Siberia, all capable of interbreeding.^[19]

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.

Ecotypes are closely related to morphs:

"(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."

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" ^[20]

The above notions may convey a sense of discrete phenomenon. But sometimes evolution acts in a continuous way so that for example 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 on this:

"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." ^[21]

See also

	Evolutionary biology portal
	Environment portal
	Ecology portal
	Earth sciences portal

• Evolution
• Adaptation
• Species
• Speciation
• Polymorphism (biology)
• Cline (biology)
• Species problem
• Ring species
• Biological classification
• Transplant experiment

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. ^ http://www.springerlink.com/content/w01617k562021220/
17. ^ Common Bottlenose Dolphin
18. ^ Encyclopedia of life sciences, 2007, John Wiley & Sons, "Darwin’s Finches"
19. ^ Introduction to Ecology (1983), J.C. Emberlin, chapter 8
20. ^ Begon, Townsend, Harper - Ecology: From individuals to ecosystems , Blackwell Publishing, 4th ed. (2006), p. 7
21. ^ Begon, Townsend, Harper - Ecology: From individuals to ecosystems , Blackwell Publishing, 4th ed. (2006), p. 10