Abstract
Hoplias malabaricus (Bloch, 1794), a predatory freshwater fish with a wide distribution throughout South America, represents a species complex with seven well characterized karyomorphs at the cytogenetic level. Although this species has been extensively studied in several Brazilian basins, data are still scarce for hydrographic systems from other South American countries. This study aims to characterize cytogenetically the Hoplias malabaricus populations from the Argentinean Central Region, close to the southernmost distribution of this species complex. A total of 32 specimens from the Ctalamochita River, a tributary of Lower Paraná Basin located in the province of Córdoba, were analyzed using cytogenetic techniques (Giemsa staining, C- and Ag-NOR banding and fluorescent in situ hybridization with 18S rDNA). All the specimens showed diploid number 2n=42, chromosomic formula 22m + 20sm and absence of sexual chromosomes. Thus, the analyzed populations belong to the karyomorph named A. These populations showed a remarkable degree of divergence in their cytogenetic traits such as karyotypic formula, C-banding, NORs and 18S rDNA patterns for Hoplias malabaricus from other populations bearing the same karyomorph in the Middle and Upper Paraná Basin. These findings are consistent with molecular data from a recent study (where specimens collected in the present work were included), which indicate a closer phylogenetic relationship of Hoplias malabaricus populations from the Ctalamochita River with those from the Uruguay basin and the coastal regions of South Brazil than with populations from the Middle and Upper Paraná Basin. Overall, these pieces of evidence highlight the distinctive features of Hoplias malabaricus from the Ctalamochita River, and also reveal a complex history of dispersion of these populations. The present work is the first to provide cytogenetic information and include some phylogeographic aspects of Hoplias malabaricus populations living in close proximity to the southernmost extreme of its distribution area. Therefore, this study expands significantly upon the previously known geographical coverage for karyomorph A and contributes to a better understanding of the karyotypic diversification within this species complex.
Highlights
Hoplias malabaricus (Bloch, 1794) is a predatory freshwater fish that belongs to the order Characiformes and family Erythrinidae
Several cytogenetic studies indicate that Hoplias malabaricus represents a species complex, with seven well characterized karyomorphs nominated with letters A to G, which differ with regards to their diploid numbers, chromosome morphology and the presence of sex chromosome systems (Bertollo et al 1983, 1997a, 1997b, Dergam and Bertollo 1990, Bertollo and Mestriner 1998, Born and Bertollo 2000, 2001)
The aim of the present study was characterizing at the cytogenetic level Hoplias malabaricus populations from headwater of the Ctalamochita River using standard and fluorescent in situ hybridization techniques
Summary
Hoplias malabaricus (Bloch, 1794) is a predatory freshwater fish that belongs to the order Characiformes and family Erythrinidae. It is a widespread species inhabiting 44 out of 52 South American ecoregions proposed by Abell et al (2008), in most of the hydrographic basins of South America (Oyakawa 2003). Several cytogenetic studies indicate that Hoplias malabaricus represents a species complex, with seven well characterized karyomorphs (or karyotypic variants, known as cytotypes) nominated with letters A to G, which differ with regards to their diploid numbers, chromosome morphology and the presence of sex chromosome systems (Bertollo et al 1983, 1997a, 1997b, Dergam and Bertollo 1990, Bertollo and Mestriner 1998, Born and Bertollo 2000, 2001). Two and even more karyomorphs have been found coexisting in sympatric conditions without detection of hybrid forms (Lopes and Fenocchio 1994, Scavonne et al 1994, Lopes et al 1998, Lemos et al 2002, Pazza and Júlio 2003, Born and Bertollo 2006, Da Rosa et al 2009a, 2009b, 2010)
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