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The Cichlid Fish of Cuatro Ciénegas, Mexico: Direct Evidence of Conspecificity Among Distinct Trophic Morphs

Irv Kornfield, David C. Smith, P. S. Gagnon and Jeffrey N. Taylor
Evolution
Vol. 36, No. 4 (Jul., 1982), pp. 658-664
DOI: 10.2307/2407880
Stable URL: http://www.jstor.org/stable/2407880
Page Count: 7
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
The Cichlid Fish of Cuatro Ciénegas, Mexico: Direct Evidence of Conspecificity Among Distinct Trophic Morphs
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Abstract

Two discrete cichlid fishes endemic to Cuatro Ciénegas, Mexico differ significantly in several morphological characters associated with feeding specializations. Conventional taxonomic treatment would suggest the presence of two distinct species, but Sage and Selander (1975) forcefully argued for the presence of a single polymorphic biological species. Biochemical comparisons and observations of reproduction in situ conducted in 1979, 1980, and 1981 revealed gene and genotypic homogeneity between the two types of fishes. A significant change in allele frequency at Pgi-2 which occurred between 1974 and 1980 was observed in both forms. Of cichlid pairs collected in the process of mating, 57% involved matings between forms, unequivocally suggesting the existence of a single Mendelian population. Confirmation of a trophically polymorphic biological species has significant ecological and systematic implications. Trophic polymorphism may represent an alternative strategy to adaptive radiation and may inflate estimates of species diversity based solely on phenetically defined taxa.

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