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

Simone C Girardi,Vladimir P Margarido,Carla S Pavanelli

doi:10.1590/1982-0224-20170148

Simone C Girardi, Vladimir P Margarido + Show 1 more

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https://doi.org/10.1590/1982-0224-20170148

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Abstract

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).

Highlights

Pimelodidae is an endemic fish family from the Neotropical region belonging to the order Siluriformes, and comprises 114 valid species (Eschmeyer, Fong, 2018), presents a greater diversity of species in the basins of Amazonas, Paraná and Orinoco, and greats rivers of the Guianas (Lundberg, Littman, 2003)
The 18S rDNA was located on the subtelocentric chromosome pair (24), which corresponds to the AgNORs, while the 5S rDNA was found in the pericentromeric region of the long arm of pair 18 (Fig. 3a)
The 18S rDNA was located on the subtelocentric chromosome pair (23), which corresponds to the AgNORs, while the 5S rDNA

Summary

Introduction

Pimelodidae is an endemic fish family from the Neotropical region belonging to the order Siluriformes, and comprises 114 valid species (Eschmeyer, Fong, 2018), presents a greater diversity of species in the basins of Amazonas, Paraná and Orinoco, and greats rivers of the Guianas (Lundberg, Littman, 2003). Pimelodus Lacepède, 1803 is largely distributed throughout the Neotropical region, being the most diversified genus of Pimelodidae, with approximately 34 valid species (Eschmeyer et al, 2018) This genus does not present a monophyletic hypothesis, and the inclusion of species in this genus followed the non-cladistics characters, proposed even in the 19th century, which probably will lead many species to be relocated after phylogenetic studies (Ribeiro et al, 2008; 2011). This non-monophyletism is evident in the phylogenetic study of Lundberg et al (2011), where the analyzed Pimelodus species were allocated in four clades with different genus. Fifteen species of this family have data on the location of 5S and 18S rDNA, which show variations in number and position (Tab. 1)

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