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Biochemical and Cytological Differentiation Among Cichlid Fishes of the Sea of Galilee

I. L. Kornfield, U. Ritte, C. Richler and J. Wahrman
Evolution
Vol. 33, No. 1, Part 1 (Mar., 1979), pp. 1-14
DOI: 10.2307/2407360
Stable URL: http://www.jstor.org/stable/2407360
Page Count: 14
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Biochemical and Cytological Differentiation Among Cichlid Fishes of the Sea of Galilee
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Abstract

Chromosomal and biochemical differentiation were investigated among six species of Old World cichlid fishes from the Sea of Galilee, Israel. The studied species included sympatric representatives of widespread African taxa (Sarotherodon aureus, S. galilaeus, and Tilapia zillii) and restricted Middle Eastern endemics (Haplochromis flaviijosephi, Tristramella sacra and Tr. simonis). All six species are reproductively isolated from each other. Estimates of electrophoretic similarity at 21 isozyme loci provided a temporal framework used to evaluate genetic changes. Electrophoretic similarity ranged from IN = 0.25 to IN = 0.95 and closely approximated formal taxonomic relationships among these species. Diploid chromosome number was 44 in all fishes. While cytological differentiation was minimal, some changes in chromosomal morphology were noted among genera. Differentiation included variation in the length of chromosome no. 1, relative frequency and nature of submetacentrics, and distribution of C-bands (constitutive heterochromatin). Only Haplochromis flaviijosephi contained distinct metacentric chromosomes. More detailed cytological analysis in some species revealed nucleolus-organizer regions and the presence of chromosome associations. Within Tristramella, the two very closely related species (IN = 0.95) displayed gross karyotypic similarity. Karyotypes of S. aureus and S. galilaeus were indistinguishable with general cytological stains. In both species, constitutive heterochromatin occurred in the centromeric region of all chromosomes and in the short arms of some submetacentrics. Differentiation in C-banding was noted between these species and the related tilapine T. zillii (IN = 0.49) which lacked conspicuous centromeric heterochromatin in 10 to 12 chromosomes. The quantity of DNA from erythrocyte nuclei varied significantly among the six species. Among closely related taxa, DNA was equivalent in Tr. sacra and Tr. simonis, but differed significantly within Sarotherodon. S. aureus possessed approximately 15% more nuclear DNA than S. galilaeus. Since the quantity and distribution of constitutive heterochromatin was the same in both species, it is suggested that the 'extra' DNA may be distributed interstitially throughout the genome. While chromosomal and quantitative DNA changes accompanied phyletic evolution in the six cichlids, there is no evidence that these modifications were associated with speciation.

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