Cytogenetic and comparative morphology of two allopatric populations of Astyanax altiparanae Garutti & Britski, 2000 (Teleostei: Characidae) from upper rio Paraná basin

Abstract

The recently described fish species, Astyanax altiparanae (tetra) is common in the upper rio Paraná basin, and has been reported in the Iguaçu basin. However, its natural origin in the rio Iguaçu is questionable. In the present work, karyotypical and morphological features of two populations of Astyanax altiparanae from the upper rio Tibagi and upper rio Iguaçu were compared. Both populations showed 2n=50 chromosomes and differences in their karyotype formula, NOR-bearing chromosomes and location of heterochromatin. Morphometric data from both populations were analyzed through free-size canonical variables. Cytogenetic and morphological results were mostly coincident showing exclusive markers that reflect their degree of populational isolation. In addition to other geographic, morphological and molecular data for A. altiparanae populations from the lower rio Iguaçu and rio Paraná tributaries upstream from the Itaipu Dam (South Brazil), the present results indicate that the two populations analyzed in this study belong to different stocks. The presence of this species along the rio Iguaçu basin would be a consequence of a complex and poorly understood evolutionary history.Astyanax altiparanae, recentemente descrita, é comum na bacia do alto rio Paraná, tendo sido registrada recentemente na bacia do rio Iguaçu. Entretanto, sua origem natural no rio Iguaçu é questionável. No presente trabalho algumas características cariotípicas e morfológicas de duas populações de Astyanax altiparanae do rio alto rio Tibagi e alto rio Iguaçu foram comparadas. Ambas as populações mostraram 2n=50 cromossomos e diferenças nas suas fórmulas de cariotípicas, cromossomos portadores das regiões organizadoras de nucléolos e localização da heterocromatina. Dados morfométricos das duas populações foram analisados para variáveis canônicas livres de tamanho. Os dados citogenéticos e morfológicos foram coincidentes e mostraram marcas exclusivas que refletem o grau de isolamento populacional. Em adição a outros dados geográficos, morfológicos e moleculares em populações de A. altiparanae do baixo rio Iguaçu e tributários do rio Paraná acima da represa de Itaipu (Sul do Brasil), os presentes resultados indicam que as duas populações analisadas neste estudo pertençam a diferentes estoques. A presença desta espécie ao longo da bacia do rio Iguaçu pode ser uma conseqüência de uma história evolutiva complexa e pouco conhecida.

Interpopulational comparative cytogenetics analysis among three Astyanax (Characiformes: Incertae Sedis) species of two streams of upper Paraná River basin, Brazil

“…In A. fasciatus, the presence of telomeric heterochromatin verified in the present study was also observed by other authors (Daniel-Silva & Almeida Toledo 2001;Centofante et al 2003;Pazza et al 2008). The pericentromeric heterochromatin verified in A. altiparanae seems to be preserved, as was observed in the studies that used the C banding technique (DanielSilva & Almeida Toledo 2001;Domingues et al 2007;Hashimoto et al 2008;Ferreira Neto et al 2009). …”

“…The presence of 50 chromosomes in A. fasciatus was verified by Artoni et al (2006) in the Tibagi River, an upper Paraná River affluent. As in several studies about A. altiparanae (Jim & Toledo 1975;Pacheco et al 2001;Domingues et al 2007;Hashimoto et al 2008;Ferreira Neto et al 2009), the presence of 50 chromosomes was verified in the present study. Souza & Moreira-Filho (1995) stated that the number of chromosomes carrying NORs also denotes an important factor for the differentiation among the populations.…”

“…Differences in the karyotypic formula in distinct populations have been observed in the studies of A. scabripinnis (Alves & Martins-Santos 2002), A. fasciatus (Domingues et al 2007) and A. altiparanae (Medrado et al 2008). The presence of 48 chromosomes in Astyanax scabripinnis complex was also verified in the streams of the up- Malacrida et al 2003).…”

Comparative Cytogenetic Study Among Three Fish Species: An Analysis From a Water Divide Region

“…Inter-populational karyotypic differences related to chromosomal morphology, especially concerning submetacentric and acrocentric chromosomes, could be observed in the populations from the upper Paraná basin and Iguaçu river (FERREIRA-NETO et al, 2009). Non-robertsonianos events, such as pericentric inversions could be hypotetized in the karyotypic evolution of this species (DOMINGUES et al, 2007). Thus, the karyotypic variability found in this study and among populations may be related to the occupation of different habitats that were geographically isolated, and once occurring genetic variation, these can hardly be shared.…”

“…Thus, the detection of diploid and fundamental number and the implementation of procedures generating molecular markers have been important to evolutionary analysis and cytotaxonomy these fi shes. The presence of 2n=50 chromosomes is considered the modal number for Astyanax altiparanae (FERNANDES; MARTINS-SANTOS, 2004;DOMINGUES et al, 2007;FERREIRA-NETO et al, 2009), as observed in this study too. Studies in A. altiparanae populations of the different basins present small karyotype diversifi cation.…”