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This poster, presenting selected preliminary findings of an ongoing Cichla population genetics study, was presented at the Brazilian Ichthyology Society meeting, January, 2005

Different Population Genetics Patterns in two Species of Peacock Bass
(Cichla:Perciformes) of Tributaries of the Rio Negro

Diferentes padrões genético-populacionais em duas espécies de tucunarés
(Cichla:Perciformes) de tributários do rio Negro.
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Vasconcelos, W. R. (1); Nunes, M. S (1);
Reiss, P. (2); Farias, I. P. (1).
(1) Laboratory of Evolution and
Animal Genetics - L.E.G.AL - UFAM.
(2) Acute Angling

rangel@inpa.gov.br

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Introduction

peacock bass region

The rivers Unini and Xeriuini are tributaries of the Rio Negro, itself the largest tributary of the Amazon River. They harbor a great diversity of aquatic vertebrates. To determine if the Rio Negro functions as a barrier to the genetic flow between populations of non-migratory fish, four populations of peacock bass of the species Cichla temensis and Cichla orinocensis were sampled along the above cited affluents. We used AMOVA and F statistics to test the hypothesis of population fragmentation, with the objective of identifying the patterns of distribution of intra-specific genetic variation. This information can furnish data about the evolutionary dynamics of these two economically important species, not previously studied in depth at the population level.

Materials and Methods

Tissue Samples were collected in the locations indicated on the map (Fig. 1) and were preserved in 95% ethanol. The DNA was extracted following the protocol for extraction by phenol-chloroform of Sambrook et al. (1989). The region of the gene for ATPase was amplified via PCR, with the use of primers specifically developed by Sivasundar et al., (2001). The sequencing reactions were performed in accordance with the recommendations of the manufacturers utilizing the Terminator Cycle Sequencing Kit (Amersham Bioscience), and analized in the MegaBACE 1000 automatic sequencer.

peacock bass
Fig. 2a- Example of C. orinocensis of the Rio Unini

Intra and Inter-populational Analyses

The genetic structure of the populations was analyzed using AMOVA (Analysis of Molecular Variance) (Excoffier et al., 1992), and pairwise FsT (Cockerham & Weir, 1993), implemented by the program Harlequin 2.0 (Schneider et al., 2000). Indices of genetic diversity and tests of selective neutrality of mutations were accessed using the program Harlequin 2.0. The haplotype network was constructed with the program TCS versão 1.18 (Clement et al., 2000).

 

peacock bass
Fig. 2b- Example of C. temensis of the Rio Unini

Results and Discussions

Based on the analyses of 605 base pairs and 46 gene copies, we found 11 haplotypes in C. temensis, with 1 most frequent and 9 singularly occuring. While in the two populations of C. orinocensis, we analyzed 25 gene copies, we found 10 haplotypes, 3 being more frequent in relation to the rest. Values of genetic diversity in general were more elevated in the populations of C. orinocensis than in C. temensis (Tab. 1). The neutral presumption of mutations was tested through the index of selective neutrality Fs of Fu and indicated genetic disequilibrium in the population of C. orinocensis and C. temensis of the rio Unini (Tab. 1). Meanwhile D of Tajima indicated a probable population growth only in C. temensis. Significant values (P<0,05) of the parameter Fst were observed between the populations of C. orinocensis, even with the correction of Bonferroni (Rice 1989).

peacock bass DNA chart
Fig. 3a -Haplotype network showing the geneological relationships between the ten haplotypes detected and identified in C. orinocensis. The color black indicates haplotypes found on the Rio Unini and yellow indicates those of the Rio Xeriuini.
peacock bass DNA chart
Fig. 3b -Haplotype network showing the geneological relationships between the ten haplotypes detected and identified in C. temensis. The color black indicates haplotypes found on the Rio Unini and yellow indicates those of the Rio Xeriuini.
Tab. 1- Principal measures of intra-specific genetic polymorphism and tests of selective neutrality. P<0.05.
Note: RU=Rio Unini and RX=Rio Xeriuini
Population No. of
samples
No. of
Polymorphic sites
Genetic Diversity Nucleotide Diversity D of Tajima Fsof Fu
RU-C. orinocensis 11 10 0.9333 +/- 0.0773 0.005657 +/- 0.003569 -0.14123 -3.11607 *
RX-C. orinocensis 14 10 0.8901 +/- 0.0603 0.005657 +/- 0.003569 -0.68577 -2.09245
RU-C. temensis 32 4 0.3377 +/- 0.1278 0.000601 +/- 0.000672 -1.87763 * -3.81699 *
RX-C. temensis 14 3 0.2949 +/- 0.1558 0.000763 +/- 0.000802 -1.65231 * -0.68877

 

Table 2a - Values of Pairwise Fst below the line and Effective number of migrants (Nm) above the line for C. orinocensis.
Note: RU=Rio Unini and RX=Rio Xeriuini.
Population RU-C. orinocensis RX-C. orinocensis
RU-C. orinocensis ______________ 84186
RX-C. orinocensis 0.23878 * ______________
Table 2b -Values of Pairwise Fst below the line and Effective number of migrants (Nm) above the line for C. orinocensis. C. temensis.
Note: RU=Rio Unini and RX=Rio Xeriuini.
Population RU- C. temensis RX- C. temensis
RU- C. temensis ______________
RX- C. temensis 0 ______________

 

No indication of genetic difference was demonstrated in the two populations of C. temensis, an indication of elevated genetic flux. () (Tab. 3b).

The results of AMOVA also show this pattern. In the populations of C. orinocensis, 37,26% of the genetic variation occurred between the two populations (Fst=0,372; P=0). While in C. temensis, the variation between the two populations was -0,97% (Fst=-0,0096; P=0.7575). Fst and AMOVA indicate population fragmentation in C. orinocensis.

These results demonstrate that a distance of ~100 Km between tributaries of the Rio Negro can function as a barrier to the dispersion of some species of fish as seen in C. orinocensis, but not in others as in C. temensis. Species of peacock bass , for example, can exhibit different patterns of migration, reflectining different life strategies.

Funding

IFS logo
International Foundation for Science
peacock bass
Acute Angling Sport Fishing

Bibliography and References

Clement, M.; Posada, D. and Crandall, K. A. (2000) TCS: a computer program to estimate gene 6 genealogies. Mol. Ecol., 9, 1657-1659.

Cockerham, C. C. and Weir B. S. (1993) Estimation of gene flow from F-statistics. Evolution, 47, 855-863.

Excoffier, L.; Smouse, P. E. and Quattro, J. M. (1992) Analysis of molecular variance inferred from metric distances among DNA haplotypes: Application to human mitochondrial DNA restriction data. Genetics, 131, 479-491.

Rice. 1989. Analysing table of statistical tests. Evolution 43: 223-225

Sambrook, J.; Fritsch, E. F. and Maniatis, T. (1989) Molecular cloning: a laboratory manual, second edition Vol. 2. Cold Springs Harbor Laboratory Press, Cold Springs Harbor, NY.

Schneider, S.; Roessli, D. and Excoffier, L. (2000). Arlequin ver. 2000: A software for population genetic data analysis. Genetics and Biometry Laboratory, University of Geneva. Geneva, Switzerland.

Sivasundar, A.; Bermigham, E. and Orti, G. 2001. Population structure and biogeography of migratory freshwater fishes (Prochilodus: Characiformes) in major South American rivers. Mol. Ecol. 10 (2): 407-417.

Xia, X. and Xie. Z. 2001 DAMBE: Data analysis in molecular biology and evolution. Journal of Heredity 92:371-373.

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