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  Genetic and ecological divergence of a monophyletic cichlid species pair under fully sympatric conditions in Lake Ejagham, Cameroon

Schliewen, U., Rassmann, K., Markmann, M., Markert, J., Kocher, T., & Tautz, D. (2001). Genetic and ecological divergence of a monophyletic cichlid species pair under fully sympatric conditions in Lake Ejagham, Cameroon. Molecular Ecology, 10(6), 1471-1488. doi:10.1046/j.1365-294X.2001.01276.x.

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Schliewen, U.1, Author
Rassmann, K.1, Author
Markmann, M.1, Author
Markert, J.1, Author
Kocher, T.1, Author
Tautz, D.2, Author           
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1external, ou_persistent22              
2External, ou_persistent22              

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 Abstract: Although there is mounting evidence that speciation can occur under sympatric conditions, unambiguous examples from nature are rare and it is almost always possible to propose alternative allopatric or parapatric scenarios. To identify an unequivocal case of sympatric speciation it is, therefore, necessary to analyse natural settings where recent monophyletic species necks have evolved within a small and confined spatial range. We have studied such a case with a cichlid species flock that comprises five Tilapia forms endemic to a tiny lake (Lake Ejagham with a surface area of approximately 0.49 km(2)) in Western Cameroon. Analysis of mitochondrial D-Loop sequences shows that the flock is very young (approximately 10(4) years) and has originated from an adjacent riverine founder population. We have focused our study on a particular pair of forms within the lake that currently appears to be in the process of speciation. This pair is characterized by an unique breeding colouration and specific morphological aspects, which can serve as synapomorphic characters to prove monophyly. It has differentiated into a large inshore and a small pelagic form, apparently as a response to differential utilization of food resources. Still, breeding and brood care occurs in overlapping areas, both in time and space. Analysis of nuclear gene flow on the basis of microsatellite polymorphisms shows a highly restricted gene now between the forms, suggesting reproductive isolation between them. This reproductive isolation is apparently achieved by size assortative mating, although occasional mixed pairs can be observed. Our findings are congruent with recent theoretical models for sympatric speciation, which show that differential ecological adaptations in combination with assortative mating could easily lead to speciation in sympatry.

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 Dates: 2001-062001-06
 Publication Status: Issued
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Title: Molecular Ecology
Source Genre: Journal
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Publ. Info: Oxford : Blackwell Science
Pages: - Volume / Issue: 10 (6) Sequence Number: - Start / End Page: 1471 - 1488 Identifier: ISSN: 0962-1083
CoNE: https://pure.mpg.de/cone/journals/resource/954925580119