Multiple Sex Chromosomes and Evolutionary Relationships in Amazonian Catfishes: The Outstanding Model of the Genus Harttia (Siluriformes: Loricariidae).

Francisco De M C Sassi,Ezequiel Aguiar De Oliveira,Marcelo R Vicari,Geize A Deon,Thomas Liehr,Marcelo B Cioffi,Orlando Moreira-Filho,Luiz A C Bertollo

doi:10.3390/genes11101179

Abstract

The armored Harttia catfishes present great species diversity and remarkable cytogenetic variation, including different sex chromosome systems. Here we analyzed three new species, H. duriventris, H. villasboas and H. rondoni, using both conventional and molecular cytogenetic techniques (Giemsa-staining and C-banding), including the mapping of repetitive DNAs using fluorescence in situ hybridization (FISH) and comparative genomic hybridization (CGH) experiments. Both H. duriventris and H. villasboas have 2n = ♀56/♂55 chromosomes, and an X1X1X2X2 /X1X2Y sex chromosome system, while a proto or neo-XY system is proposed for H. rondoni (2n = 54♀♂). Single motifs of 5S and 18S rDNA occur in all three species, with the latter being also mapped in the sex chromosomes. The results confirm the general evolutionary trend that has been noticed for the genus: an extensive variation on their chromosome number, single sites of rDNA sequences and the occurrence of multiple sex chromosomes. Comparative genomic analyses with another congeneric species, H. punctata, reveal that the X1X2Y sex chromosomes of these species share the genomic contents, indicating a probable common origin. The remarkable karyotypic variation, including sex chromosomes systems, makes Harttia a suitable model for evolutionary studies focusing on karyotype differentiation and sex chromosome evolution among lower vertebrates.

Highlights

Siluriformes (Actinopterygii; Teleostei) is a monophyletic order that covers a large deal of the freshwater fish diversity, with more than 3000 species and 36 families [1,2]
Samples from H. punctata were used for genomic DNAs (gDNAs) extraction and comparative genomic hybridization (CGH) experiments
H. villasboas and H. duriventris have 2n = 56 chromosomes in the female specimens (18m+24sm+6st+8a in H. villasboas and 16m + 16sm + 16st + 8a in H. duriventris), but 2n = 55 chromosomes in the male specimens (19m + 24sm + 6st + 6a in H. villasboas and 17m + 16sm + 16st + 6a in H. duriventris). These specific male karyotypes are due to characteristics X1 X1 X2 X2 /X1 X2 Y multiple sex chromosome systems, where the Y corresponds to a medium-sized m chromosome (Figure 2)

Summary

Introduction

Siluriformes (Actinopterygii; Teleostei) is a monophyletic order that covers a large deal of the freshwater fish diversity, with more than 3000 species and 36 families [1,2]. Of the six Loricariidae subfamilies currently recognized, Hypostominae and Loricariinae are the most representative ones, with the highest number of species (579 and 302, respectively) and a remarkable karyotypic diversity [2,3]. The genus Harttia, popularly known as armored catfishes, is represented by 27 valid species [2,4]. Despite such great species diversity, cytogenetic studies are available for only eight of them, all from Brazilian Southern regions, with exception for Harttia punctata [3,5,6,7,8,9,10,11,12,13].

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Conclusion