Cytogenetic Studies and Evolutive Considerations in Species of the Calophysus Group (Siluriformes, Pimelodinae)

Abstract

SummaryIn this work, 2 species of the Pimelodidae family, Luciopimelodus pati and Pinirampus pirinampu, were cytogenetically analyzed. Specimens collected from the Paraná River, near Corrientes city, Argentina, were assessed using conventional Giemsa, C-banding, and AgNOR staining. L. pati and P. pirinampu showed 2nϭ50 chromosomes. The cytogenetic characteristics of the 2 species could be considered as derivate features with respect to the other Pimelodinae fishes. Chromosome fusions and chromatin loss are proposed as the hypothetical origin of the described karyotypes.

Cytogenetics of the Porthole Shovelnose Catfish, Hemisorubim platyrhynchos (Valenciennes, 1840) (Siluriformes, Pimelodidae), a widespread species in South American rivers

“…From a cytogenetic point of view some reports show that these groups could also share cytogenetic characteristics, supporting additionally the classification above mentioned ( Swarça et al 2007 , Sànchez et al 2010 , Carvalho et al 2011 ).…”

Cytogenetic studies in the redtail catfish, Phractocephalus hemioliopterus (Bloch & Schneider, 1801) (Siluriformes, Pimelodidae) a giant fish from Amazon basin

“…2a) represent common features in almost all pimelodid species analyzed so far, suggesting that these cytogenetic traits were conserved during the karyotype evolution and may have an ancient common origin (Sanchez et al 2010). The presence of ribosomal genes on the short arm of one st/a chromosome pair is coincident with the location observed in the “ Calophysus group” (Sánchez et al 2010) and “Sorubiminae group” (Swarça et al 2008) and differs from the “ Pimelodus group”, where the ribosomal genes are located almost exclusively on the long arm of m/sm chromosome pairs (Swarça et al 2007).…”

“…Available cytogenetic data partially support this hypothesis because several chromosomal studies on Pimelodidae have revealed that the species of this family have a predominant diploid number of 56 (Table 1) with a few exceptions, such as species included in the “ Calophysus group” that show some characteristic cytogenetic features as 2n = 50, reported in Calophysus Müller & Trosche, 1843, Luciopimelodus Eigenmann & Eigenmann, 1888 and Pinirampus Bleeker, 1858 (Ramirez-Gil et al 1998, Swarça et al 1999, Sanchez et al 2010) and Megalonema platanum (Günther, 1880) with 2n = 54 (Carvalho et al 2011). According to phylogenetic tree of Lundberg and Littman (2003) the branch that includes Leiarius , Perrunichthys and Phractocephalus has been never studied cytogenetically; this fact demonstrates that more species must be chromosomally studied to increase the number of cytogenetic data to better understand the species relationships and the karyotypic evolution in this fish group.…”