Cytogenetic studies have shown that the genus Astyanax has extensive karyotypic variability among species and many are the works developed about this group in different river basins in Brazil. The Tangara da Serra ar...Cytogenetic studies have shown that the genus Astyanax has extensive karyotypic variability among species and many are the works developed about this group in different river basins in Brazil. The Tangara da Serra area （Mato Grosso State, Brazil）, which contains tributaries of both Amazon and Upper Paraguay River basins is, therefore, a natural watershed. Thus, in this work, the karyotypes of three species of Astyanax from the Sepotuba River＇s tributary streams were analyzed by using conventional methods of chromosome analysis. Astyanax marionae presented 2n =48（12m＋ 10sm＋ 12st＋ 14a） and NF （fundamental number） = 82 with evident heterochromatin in several chromosomal regions. Astyanax cf. asuncionensis presented 2 n = 50 （20m ＋ 12sm ＋ 6st ＋ 12a）, NF = 94 chromosomes and with evident heterochromatin in few chromosomes and Ag-NOR in one chromosome pair. Astyanax cp. scabripinnis presented 2 n = 50 （12m ＋ 10sm ＋ 10st ＋ 18a）, NF = 82 with evident heterochromatin at most of the chromosomes in pericentromeric region and a strongly marked block on a telocentric chromosome pair. The Ag-NORs were observed near the heterochromatic region. The karyotypic differences found, probably occurred by chromosomal rearrangements, resulting in a heterogeneous model of chromosomal evolution who probably involved both Robertsonian chromosomal rearrangements to A. marionae, as not Robertsonian to other Astyanax species. This indicates that although these species share the same hydrographic basin （Upper Paraguay） are isolated in different microbasins and the absence in the gene flow may have allowed the establishment of independent rearrangements in each population.展开更多
文摘Cytogenetic studies have shown that the genus Astyanax has extensive karyotypic variability among species and many are the works developed about this group in different river basins in Brazil. The Tangara da Serra area （Mato Grosso State, Brazil）, which contains tributaries of both Amazon and Upper Paraguay River basins is, therefore, a natural watershed. Thus, in this work, the karyotypes of three species of Astyanax from the Sepotuba River＇s tributary streams were analyzed by using conventional methods of chromosome analysis. Astyanax marionae presented 2n =48（12m＋ 10sm＋ 12st＋ 14a） and NF （fundamental number） = 82 with evident heterochromatin in several chromosomal regions. Astyanax cf. asuncionensis presented 2 n = 50 （20m ＋ 12sm ＋ 6st ＋ 12a）, NF = 94 chromosomes and with evident heterochromatin in few chromosomes and Ag-NOR in one chromosome pair. Astyanax cp. scabripinnis presented 2 n = 50 （12m ＋ 10sm ＋ 10st ＋ 18a）, NF = 82 with evident heterochromatin at most of the chromosomes in pericentromeric region and a strongly marked block on a telocentric chromosome pair. The Ag-NORs were observed near the heterochromatic region. The karyotypic differences found, probably occurred by chromosomal rearrangements, resulting in a heterogeneous model of chromosomal evolution who probably involved both Robertsonian chromosomal rearrangements to A. marionae, as not Robertsonian to other Astyanax species. This indicates that although these species share the same hydrographic basin （Upper Paraguay） are isolated in different microbasins and the absence in the gene flow may have allowed the establishment of independent rearrangements in each population.
