Cytotaxonomy of Parodon nasus and Parodon tortuosus (Pisces, Characiformes): A case of synonymy confirmed by cytogenetic analyses

Abstract

Morphological and cytogenetical studies were carried out on the freshwater fish Parodon nasus and Parodon tortuosus in order to evaluate a putative synonymy. The diploid chromosome number observed in both species was 2n = 54 (48M/SM and 6ST) with no differences between the sexes. Despite slight differences in the pattern of heterochromatin distribution and the number of cusps in symphysean teeth, the location of nucleolar organizer regions (NORs) and 5S rRNA genes (both species-specific features) were similar in both species. The remarkable similarity observed between these allopatric species supports recent taxonomical reviews indicating that P. tortuosus is a synonym for P. nasus

Karyotypic diversity and chromosome evolution in the armored catfishes Callichthyinae (Siluriformes, Callichthyidae)

“…The results obtained with this chromosomal marker suggest that the ribosomal genes were dispersed to more chromosome pairs during the chromosomal differentiation in Callichthyinae (Figure 2a, b, c). NORs can be important cytotaxonomic markers (Bellafronte et al 2005); the primitive character simple NORs observed in Olivaichthys mesembrinus (Oliveira and Gosztonyi 2000) and in Loricariidae (Alves et al 2005) were shown to be conserved regarding the number of sites for Callichthys and Hoplosternum; Lepthoplosternum showed multiple sites with varied positions, indicating the occurrence of events responsible for the change and dispersion of this region (Figure 2). This wide dispersion could be related to the association of heterochromatin to these regions, which characterizes regions more favorable to chromosomal breakages and rearrangements (Margarido and Galetti 2000;Souza et al 2001).…”

“…NORs (Ag-staining and 18S rDNA) have been used as an efficient chromosomal marker in some Neotropical fishes (Artoni and Bertollo 2001;Alves et al 2005;Bellafronte et al 2005;Mariotto et al 2011). In Siluriformes, the most basal species Olivaichthys mesembrinus (Oliveira and Gosztonyi 2000) shows single NORs.…”

“…Cytogenetics has contributed toward the characterization of species in studies on cytotaxonomy (Bertollo et al 1978;Moreira-Filho and Bertollo 1991;Bellafronte et al 2005;Fernandes and Martins-Santos 2005) and cytosystematics Margarido and Galetti 1999;Artoni and Bertollo 2001).…”

“…Physical mapping studies of 5S and 18S rDNA have contributed to the cytotaxonomy and/or cytosystematics of different groups, e.g. Parodontidae (Bellafronte et al 2005), in Gymnotus (Silva et al 2011a), in Ancistrus (Mariotto et al 2011), in Pimelodus (Garcia and Moreira-Filho 2008), in Erythrinus (Blanco et al 2011), and in Loricariidae (Ziemniczak et al 2012).…”

Chromosome mapping of 18S rDNA and 5S rDNA by dual-color fluorescence in situ hybridization in the half-smooth tongue sole (Cynoglossus semilaevis)

“…According to these previous studies, the location patterns between the major and minor rDNA sites are usually diverse among different families and conserved within the same family. In Parodon species, however, the localizations of both rDNAs are species-specific and can serve as genetic markers (Bellafronte et al, 2005). The synteny of 18S and 5S rDNA has been considered as an ancestral status in the fish genome (Fontana et al, 2003), but their non-synteny can prevent undesirable translocations of 5S sequences within 45S rDNA during evolution (Martins and Galetti, 1999).…”