Sympatry
In biology, two related
Types of populations
Four main types of population pairs exist in nature. Sympatric populations (or species) contrast with
Evolving definitions and controversy
The lack of geographic isolation as a definitive barrier between sympatric species has yielded controversy among ecologists, biologists, botanists, and zoologists regarding the validity of the term. As such, researchers have long debated the conditions under which sympatry truly applies, especially with respect to parasitism. Because parasitic organisms often inhabit multiple hosts during a life cycle, evolutionary biologist Ernst Mayr stated that internal parasites existing within different hosts demonstrate allopatry, not sympatry. Today, however, many biologists consider parasites and their hosts to be sympatric (see examples below). Conversely, zoologist Michael J. D. White considered two populations sympatric if genetic interbreeding was viable within the habitat overlap. This may be further specified as sympatry occurring within one deme; that is, reproductive individuals must be able to locate one another in the same population in order to be sympatric.
Others question the ability of sympatry to result in complete speciation: until recently, many researchers considered it nonexistent, doubting that selection alone could create disparate, but not geographically separated, species. In 2003, biologist Karen McCoy suggested that sympatry can act as a mode of speciation only when "the probability of mating between two individuals depend[s] [solely] on their genotypes, [and the genes are] dispersed throughout the range of the population during the period of reproduction".[4] In essence, sympatric speciation does require very strong forces of natural selection to be acting on heritable traits, as there is no geographic isolation to aid in the splitting process. Yet, recent research has begun to indicate that sympatric speciation is not as uncommon as was once assumed.
Syntopy
Syntopy is a special case of sympatry. It means the joint occurrence of two
As an example, the two bat species
Sympatric speciation
The lack of geographic constraint in isolating sympatric populations implies that the emerging species avoid interbreeding via other mechanisms. Before speciation is complete, two diverging populations may still produce viable offspring. As speciation progresses,
Species discrimination
Sympatric groups frequently show a greater ability to discriminate between their own species and other closely related species than do allopatric groups. This is shown in the study of hybrid zones. It is also apparent in the differences in levels of prezygotic isolation (by factors that prevent formation of a viable zygote) in both sympatric and allopatric populations. There are two main theories regarding this process: 1) differential fusion, which suggests that only populations with a keen ability to discriminate between species will persist in sympatry; and 2) character displacement, which implies that distinguishing characteristics will be heightened in areas where the species co-occur in order to facilitate discrimination.
Reinforcement
Reinforcement is the process by which natural selection reinforces reproductive isolation. In sympatry, reinforcement increases species discrimination and sexual adaptation in order to avoid maladaptive hybridization and encourage speciation. If hybrid offspring are either sterile or less-fit than non-hybrid offspring, mating between members of two different species will be selected against. Natural selection decreases the probability of such hybridization by selecting for the ability to identify mates of one's own species from those of another species.
Reproductive character displacement
Reproductive character displacement strengthens the reproductive barriers between sympatric species by encouraging the divergence of traits that are crucial to reproduction. Divergence is frequently distinguished by
Differential fusion
An alternative explanation for species discrimination in sympatry is differential fusion. This hypothesis states that of the many species have historically come into contact with one another, the only ones that persist in sympatry (and thus are seen today) are species with strong mating discrimination. On the other hand, species lacking strong mating discrimination are assumed to have fused while in contact, forming one distinct species.
Differential fusion is less widely recognized than character displacement, and several of its implications are refuted by experimental evidence. For example, differential fusion implies greater postzygotic isolation among sympatric species, as this functions to prevent fusion between the species. However, Coyne and Orr found equal levels of postzygotic isolation among sympatric and allopatric species pairs in closely related Drosophila.[8] Nevertheless, differential fusion remains a possible, though not complete, contributor to species discrimination.[9]
Examples
Sympatry has been increasingly evidenced in current research. Because of this, sympatric speciation – which was once highly debated among researchers – is progressively gaining credibility as a viable form of speciation.
Orca: partial sympatry
Several distinct types of
Great spotted cuckoo and magpie: brood parasitism
The parasitic great spotted cuckoo (Clamator glandarius) and its magpie host, both native to Southern Europe, are completely sympatric species. However, the duration of their sympatry varies with location. For example, great spotted cuckoos and their magpie hosts in Hoya de Gaudix, southern Spain, have lived in sympatry since the early 1960s, while species in other locations have more recently become sympatric. Great spotted cuckoos, when in South Africa, are sympatric with at least 8 species of starling and 2 crows, pied crow and Cape crow.[11]
The great spotted cuckoo exhibits
Acromyrmex ant: isolation of fungal gardens
See also
- Evolutionary pressure
- Ring species
- Selection
- Pieris oleracea
References
- ^ Futuyma 2009, pp. 448, G-9.
- ^ Futuyma 2009, p. 241.
- ^ Futuyma 2009, pp. 487–490.
- ^ McCoy 2003.
- JSTOR 30055386.
- ISSN 0173-5373.
- ^ Dieckmann & Doebeli 1999.
- ^ Coyne & Orr 1989.
- ^ Noor 1999.
- ^ Foote et al. 2011.
- ^ Roberts & Tarboton 2011.
- ^ Soler & Moller 1990.
- ^ Bot, Rehner & Boomsma 2001.
Bibliography
- Bot, A.N.M.; Rehner, S.A. & Boomsma, J.J. (October 2001). "Partial Incompatibility between Ants and Symbiotic Fungi in Two Sympatric Species of Acromyrmex Leaf-Cutting Ants". Evolution. 55 (10): 1980–1991. S2CID 25817643.
- Coyne, Jerry A. & Orr, H. Allen (March 1989). "Patterns of Speciation in Drosophila". Evolution. 43 (2): 362–381. S2CID 1678429.
- Dieckmann, U. & Doebeli, M. (July 1999). "On the origin of species by sympatric speciation" (PDF). Nature. 400 (6742): 354–357. S2CID 4301325.
- Foote, A.D.; Morin, P.A.; Durban, J.W.; et al. (September 2011). "Out of the pacific and back again: insights into the matrilineal history of pacific killer whale ecotypes". PLOS ONE. 6 (9): e24980. PMID 21949818.
- Futuyma, D.J. (2009). Evolution (2nd ed.). Sunderland, Massachusetts: ISBN 978-0-87893-223-8.
- McCoy, K.D. (September 2003). "Sympatric speciation in parasites – what is sympatry?". Trends in Parasitology. 19 (9): 400–404. PMID 12957516.
- Noor, M.A.F. (November 1999). "Reinforcement and other consequences of sympatry" (PDF). Heredity. 83 (5): 503–508. S2CID 26625194.
- ISBN 978-0-620-50629-8.
- Soler, M. & Moller, A.P. (February 1990). "Duration of sympatry and coevolution between the great spotted cuckoo and its magpie host". Nature. 343 (6260): 748–750. S2CID 4326684.