Abstract
Four populations of Astyanax aff. fasciatus of the upper rio Tibagi (municipal district of Ponta Grossa, Paraná State, Brazil), had their karyotypes and morphometry analyzed. The cytogenetic data show the occurrence of distinct karyotypes (cytotypes), here named cytotype A, with 2n=48 chromosomes (6m+18sm+14st+10a), cytotype B, with 2n=50 chromosomes (8m+18sm+14st+10a) and cytotype C, with 2n=50 chromosomes (8m+18sm+14st+10a). The distribution pattern of the constitutive heterochromatin was very similar between cytotypes A and B, but diverged in relation to cytotype C. Distinct cytotypes may occur in sympatry in the upper rio Tibagi region, with the exception of the Furna 2 sample, which presents cytotype A exclusively. In addition, a specimen with 2n=49 chromosomes (7m+18sm+14st+10a) was also found and, by the characteristics presented, may be a consequence of a rare hybridization event between cytotypes A and B. The morphometric analyses of canonical variates indicate a consistent isolation of the Furna 2 sample, while the other samples seem to be superimposed, indicating a possible gene flow or even a recent isolation event. This model points to a probable complex of cryptic species in the studied region.
Highlights
The freshwater ichthyofauna of the Neotropical region is the most diverse of the world, being estimated in more than 8,000 species (Schaefer, 1998)
Astyanax aff. fasciatus: species complex with sympatric cytotypes biochemical studies have demonstrated that populations of many nominal species are differentiated, as is seen in Astyanax scabripinnis (Caramaschi, 1986; Moreira-Filho & Bertollo, 1991; Maistro et al, 1998; Munim et al, 2004) and Astyanax fasciatus (Justi, 1993; Centofante et al, 2003)
The present work analyzes Astyanax aff. fasciatus samples occurring in the region of the upper rio Tibagi and its affluents in regards to karyotypic evolution
Summary
The freshwater ichthyofauna of the Neotropical region is the most diverse of the world, being estimated in more than 8,000 species (Schaefer, 1998). The rio Tibagi, object of the present study, is an affluent of the left bank of the rio Paranapanema which, in turn, discharges in the Paraná river in its upper course, above the Sete Quedas region, belonging, to the upper Paraná system (Medri et al, 2002). Biochemical studies have demonstrated that populations of many nominal species are differentiated, as is seen in Astyanax scabripinnis (Caramaschi, 1986; Moreira-Filho & Bertollo, 1991; Maistro et al, 1998; Munim et al, 2004) and Astyanax fasciatus (Justi, 1993; Centofante et al, 2003). Fasciatus samples occurring in the region of the upper rio Tibagi and its affluents in regards to karyotypic evolution. Different karyotypic forms that may be found in a sympatric condition were detected
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