First cytogenetic analysis of Ichthyoelephas humeralis (Günther, 1860) by conventional and molecular methods with comments on the karyotypic evolution in Prochilodontidae

Mauro Nirchio Tursellino,Wilmer Arnoldo Moreira Blacio,César Quezada Abad,Duílio Mazzoni Zerbinato De Andrade Silva,Omar Rogerio Sánchez Romero,Claudio Oliveira

doi:10.3897/compcytogen.v10i4.9858

Abstract

We used conventional cytogenetic techniques (Giemsa, C-banding, Ag-NOR), and fluorescent in situ hybridization (FISH) with 5S and 18S rDNA probes to investigate the karyotype and cytogenetic characteristics of Ichthyoelephas humeralis (Günther, 1860) from Ecuador. The specimens studied have a karyotype with 2n=54 biarmed chromosomes (32 M + 22 SM) and C-positive heterochromatin located on the centromeric, pericentromeric, interstitial, and terminal regions of some chromosomes. The nucleolus organizer regions occurred terminally on the long arm of chromosome pair 2. FISH confirmed the presence of only one 18S rDNA cluster with nonsyntenic localization with the 5S rDNA. Cytogenetic data allow us to refute the earlier morphological hypothesis of a sister relationship between Semaprochilodus Fowler, 1941 and Ichthyoelephas Posada Arango, 1909 and support the molecular proposal that Ichthyoelephas is a sister group to the monophyletic clade containing Prochilodus Agassiz, 1829 and Semaprochilodus.

Highlights

The fish family Prochilodontidae includes 21 valid species, with three recognized genera: Ichthyoelephas Posada Arango, 1909, Prochilodus Agassiz, 1829 and Semaprochilodus Fowler, 1941 (Castro and Vari 2004, Eschmeyer and Fong 2016)
Cytogenetic studies conducted with 12 representatives of the genera Prochilodus and Semaprochilodus show that they have an evolutionarily conserved karyotype with 2n=54 biarmed elements, composed of 40 metacentric and 14 submetacentric chromosomes with a fundamental number (FN)=108 (Arai, 2011)
The present data about I. humeralis confirm the occurrence of a conservative chromosome diploid complement and fundamental number in Prochilodontidae

Summary

Introduction

The fish family Prochilodontidae includes 21 valid species, with three recognized genera: Ichthyoelephas Posada Arango, 1909, Prochilodus Agassiz, 1829 and Semaprochilodus Fowler, 1941 (Castro and Vari 2004, Eschmeyer and Fong 2016). These species constitute a valuable resource of commercial and subsistence freshwater fish distributed throughout the South American countries, except Chile (Lowe-McConnell 1975, Goulding 1981, Flecker 1996). Cytogenetic studies conducted far in Prochilodontidae are limited to Prochilodus (8/13 species karyotyped) and Semaprochilodus (4/6 species karyotyped). No cytogenetic data are available for the two Ichthyoelephas species, Ichthyoelephas longirostris (Steindachner, 1879), and Ichthyoelephas humeralis (Günther, 1860)

Methods

Results

Conclusion