Contributions to the systematic of Pimelodidae (Osteichthyes, Siluriformes): basic and molecular cytogenetics on seven species of Pimelodus from three Brazilian hydrographic systems

Abstract

Pimelodidae harbors several species and is widely distributed throughout the Neotropical region. Pimelodus is the genus with the largest number of species, however it is a polyphyletic group. Cytogenetic analyzes of the valid species still covers less than half of them. Herein, seven Pimelodus species from three Brazilian hydrographic systems were analyzed through basic (Giemsa, AgNORs and C banding) and molecular (5S and 18S rDNA-FISH) cytogenetic methods. All species had 2n=56 chromosomes with different karyotype formulas observed among the species. AgNORs were corresponding to 18S rDNA and localized on long arm of one chromosome pair in all species. Heterochromatin distribution follows the pattern commonly verified in the family and allows to identify each one of the studied species. 5S rDNA marker was interspecifically variable in number and position of cistrons. Pimelodus ortmanni had B chromosomes varying intra and inter-individually. We performed a discussion on our own and available cytogenetic data for Pimelodidae, and the associating of them with available phylogeny enable us identifying features that distinguish subgroups within Pimelodidae, such as NORs location (terminal/long arm for species belonging to “Iheringichthys-Parapimelodus” and “Pimelodus maculatus” subclades) and location of 5S rDNA sites (pericentromeric/interstitial/ long arm for species belonging to Pimelodus group).

Integrative taxonomy reveals hidden cestode diversity in Pimelodus catfishes in the Neotropics

“…This unusual number of proteocephalids in a small‐sized pimelodid catfish may reflect the assumption that Pi. maculatus represents a species complex (Girardi et al., 2018). A recent phylogenetic study using DNA barcoding (COI) sequences of fishes from the Pantanal floodplain and upper Paraná River (localities also sampled in this study) has revealed the presence of two discrete species within the Pi.…”

Karyotype Evolution of Talking Thorny Catfishes Anadoras (Doradidae, Astrodoradinae): A Process Mediated by Structural Rearrangements and Intense Reorganization of Repetitive DNAs

“…Several studies demonstrate that pericentric inversions can promote genetic incompatibilities among species, an important mechanism of postzygotic isolation [Noor et al, 2001;Kirkpatrick and Barton, 2006]. Pericentric inversions have been frequently detected in many groups of fish, especially among the Siluriformes where they are considered the major rearrangements in the karyotype diversification in Loricariichthys [Takagui et al, 2014], Rineloricaria [Venturelli et al, 2021], Trachelyopterus [Santos et al, 2021], Tatia [Lui et al, 2013a], Pimelodus [Girardi et al, 2018], and Trichomycterus [Oliveira et al, 2016]. Among Doradidae, multiple pericentric inversions events associated with heterochromatin movements occurred independently in several clades and played a key role in the diversification of Wertheimerinae [Eler et al, 2007;Takagui et al, 2019] and Doradinae subfamilies, especially in the large species allocated in the nonfimbriated barbels clade [Milhomem et al, 2008;Baumgärtner et al, 2018;Takagui et al, 2021] and in the widespread species T. paraguayensis [Baumgärtner et al, 2016].…”