Abstract
ABSTRACT Parodontidae is a relatively small group of Neotropical characiform fishes consisting of three genera (Apareiodon, Parodon, and Saccodon) with 32 valid species. A vast cytogenetic literature is available on Apareiodon and Parodon, but to date, there is no cytogenetic data about Saccodon, a genus that contains only three species with a trans-Andean distribution. In the present study the karyotype of S. wagneri was described, based on both conventional (Giemsa staining, Ag-NOR, C-bands) and molecular (repetitive DNA mapping by fluorescent in situ hybridization) methods. A diploid chromosome number of 2n = 54 was observed in both sexes, and the presence of heteromorphic sex chromosomes of the ZZ/ZW type was detected. The W chromosome has a terminal heterochromatin band that occupies approximately half of the long arm, being this band approximately half the size of the Z chromosome. The FISH assay showed a synteny of the 18S-rDNA and 5S-rDNA genes in the chromosome pair 14, and the absence of interstitial telomeric sites. Our data reinforce the hypothesis of a conservative karyotype structure in Parodontidae and suggest an ancient origin of the sex chromosomes in the fishes of this family.
Highlights
The Neotropical region has the largest repository of freshwater fish species that correspond to about 16% of the world’s fish biodiversity (Albert, Reis, 2011; Reis et al, 2016)
The fishes were collected with cast nets and placed in plastic bags filled up to a third of their capacity with water and oxygen the remaining two thirds, transported in cardboard boxes to the laboratory where they were confined in aquariums provided with constant aeration until they were processed
This is due to the presence of morphologically differentiated sex chromosomes, i.e., to a heteromorphic ZZ/ZW sex chromosome system
Summary
The Neotropical region has the largest repository of freshwater fish species that correspond to about 16% of the world’s fish biodiversity (Albert, Reis, 2011; Reis et al, 2016). This order includes exclusively freshwater fishes distributed in both Africa and America and shows its greatest diversity in the Neotropical Region (Malabarba, 1998; Nelson et al, 2016). Parodontidae is a relatively small family distributed throughout South America and part of Panama (Nelson et al, 2016), and includes 32 species (Fricke et al, 2020a) organized in three genera: Apareiodon Eigenmann, 1916 (N = 15), Parodon Valenciennes, 1850 (N = 14) and Saccodon Kner, 1863 (N = 3) that differ due to some subtle morphological characters (Pavanelli, 2003)
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