Constitutive heterochromatin heteromorphism in the Neotropical armored catfish Hypostomusregani (Ihering, 1905) (Loricariidae, Hypostominae) from the Paraguay River basin (Mato Grosso do Sul, Brazil).

Greicy Ellen De Brito Ferreira,Ligia Magrinelli Barbosa,Ana Camila Prizon-Nakajima,Luciana Andreia Borin-Carvalho,Isabel Cristina Martins-Santos,Raquel Bozini Gallo,Claudio Henrique Zawadzki,Margarida Maria De Rossi Vieira,Renata De Rosa,Suzana De Paiva,Ana Luiza De Brito Portela-Castro

doi:10.3897/compcytogen.v13i1.30134

Abstract

A cytogenetic analysis based on the integration of a number of different chromosomal methodologies, including chromosome microdissection was carried out to characterize the chromosomally polymorphic Hypostomusregani population from the Paraguay River basin, state of Mato Grosso do Sul in Brazil. All specimens had 2n=72 (FN=116) but two distinct karyotype formulas: karyomorph A (12m+14sm+18s+28a) and karyomorph B (13m+14sm+17st+28a). Karyomorph A and B differed only for pair 19 that consisted of two subtelocentrics in karyomorph A and a large metacentric and a subtelocentric in karyomorph B. This heteromorphism was due to extensive heterochromatinization of the short arm of the large metacentric, as highlighted by C-banding. The microdissection of the large metacentric of pair 19 allowed the production of a probe, named HrV (Hypostomusregani Variant), that hybridized to the whole p arm of the large metacentric and the pericentromeric region of the short arm of its (subtelocentric) homologue (karyomorph B) and of both homologs of pair 19 in karyomorph A. Additional cytogenetic techniques (FISH with 18S and 5S rDNA probes, CMA3 and DAPI staining) allowed a finer distinction of the two karyomorphs. These results reinforced the hypothesis that the novel large metacentric of H.regani (karyomorph B) was the result of the amplification of heterochromatin segments, which contributed to karyotypic diversification in this species.

Highlights

Hypostomus Lacépède, 1803 is the most species-rich catfish genus in the Neotropical subfamily Hypostominae (Loricariidae), which comprises around 135 species (Zawadzki et al 2016)
All Hypostomus regani specimens had a diploid number of 72 chromosomes (FN=116), but two different karyotypic formulas
Hypostomus regani karyotypes were characterized by a chromosomal polymorphism involving a structural change in a single chromosome pair, subtelocentric pair 19, which resulted in an asymmetry in the karyotype formulas in the analyzed specimens

Summary

Introduction

Hypostomus Lacépède, 1803 is the most species-rich catfish genus in the Neotropical subfamily Hypostominae (Loricariidae), which comprises around 135 species (Zawadzki et al 2016). Scarce, available data on the heterochromatin of Hypostomus species indicate a great diversity in its amount and constitution (Artoni and Bertollo 1999, Kavalco et al 2004, Bittencourt et al 2011a, Traldi et al 2012, Baumgärtner et al 2014, Kamei et al 2017). One of the first analyses of the genomic distribution of heterochromatin in Hypostomus revealed two general distribution patterns: (i) species with a small amount of heterochromatin, located in subterminal and/or centromeric regions, and (ii) species with a large number of heterochromatic regions located in interstitial sites in several acrocentric chromosomes (Artoni and Bertollo 1999, 2001)

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Conclusion