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| Author(s): |
Riviane Garcez da Silva
Total Authors: 1
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| Document type: | Master's Dissertation |
| Press: | São Paulo. |
| Institution: | Universidade de São Paulo (USP). Instituto de Biociências (IBIOC/SB) |
| Defense date: | 2006-10-19 |
| Examining board members: |
Lurdes Foresti de Almeida Toledo;
Sergio Russo Matioli;
Claudio de Oliveira
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| Advisor: | Lurdes Foresti de Almeida Toledo |
| Abstract | |
Prochilodus lineatus has a commercial importance in the Brazilian freshwater fishing, especially in the Rio Grande basin. Several studies have been done with P. lineatus in this area, including those delimiting populations. Since then, the Rio Grande basin has been changed due to environmental impacts caused by construction of several dams. The most expressive impact for this population of P. lineatus was the impossibility of upstream migration, essential for its reproduction. The present study aimed at genetically verifying the impact of dams in the population of P. lineatus from Rio Grande basin. The PCR-RFLP method was used in mitochondrial DNA fragments ND2-CO1 and control region, with 10 and 15 restriction enzymes, respectively. Nine samples colected between dams with no fish ladders were analyzed: in Rio Grande - Cardoso, Colômbia, Conceição das Alagoas, Igarapava, Pedregulho e São João Batista do Glória; in Rio Mogi-Guaçu - Pirassununga e Espírito Santo do Pinhal; and in Rio Pardo Jaborandi. Analysis results of the ND2-CO1 fragment with three samples, one from each river, did not show significant divergence. Values of haplotype and nucleotide diversity were low when compared to other fish species. These results are expected for conserved sequences, so analysis of a more variable region, such as the control region, was chosen. Results of the control region (Fst, Monte Carlo distribution, exact test and AMOVA) showed a significant divergence between Jaborandi sample and the others. This could be due to a population structure, or to an error in the locality identification. The other samples seem to be part of a single population. Isolation by distance was not verified since there is no correlation between genetic and geographic distances. Values of haplotype and nucleotide diversity ranged from high to moderate, with the highest values found in samples from localities where natural features of the basin still exist. Presence of few and widely distributed haplotypes internally in the haplotype net, and the occurrence of several other rare haplotypes distributed peripherically in the haplotype net, are typical of a recent population expansion. The expansion was also verified in neutrality tests and mismatch distribution. The calculated expansion time is 238 thousands of years that correspond to the Median Pleistocene, a period of great climatic changes in South America. In conclusion, the environmental changes caused by dams did not generate significant differences among the analyzed samples, in a short-term, and did not seem to be decreasing the genetic variability of P. lineatus, when compared to other natural populations. Divergence obtained for Jaborandi should be better studied, but seems to reflect the absence of gene flow prior to the construction of dams. These work intents to present a comparative parameter for future studies, especially those monitoring the genetic variability of P. lineatus. Longterm studies must be conducted to help fisheries management of P. lineatus, including restock programs. (AU) | |