Cytogenetic characterization of Hypostomus soniae Hollanda-Carvalho & Weber, 2004 from the Teles Pires River, southern Amazon basin: evidence of an early stage of an XX/XY sex chromosome system

Abstract

In the present study, we analyzed individuals of Hypostomus soniae (Loricariidae) collected from the Teles Pires River, southern Amazon basin, Brazil. Hypostomus soniae has a diploid chromosome number of 2n = 64 and a karyotype composed of 12 metacentric (m), 22 submetacentric (sm), 14 subtelocentric (st), and 16 acrocentric (a) chromosomes, with a structural difference between the chromosomes of the two sexes: the presence of a block of heterochromatin in sm pair No. 26, which appears to represent a putative initial stage of the differentiation of an XX/XY sex chromosome system. This chromosome, which had a heterochromatin block, and was designated proto-Y (pY), varied in the length of the long arm (q) in comparison with its homolog, resulting from the addition of constitutive heterochromatin. It is further distinguished by the presence of major ribosomal cistrons in a subterminal position of the long arm (q). The Nucleolus Organizer Region (NOR) had different phenotypes among the H. soniae individuals in terms of the number of Ag-NORs and 18S rDNA sites. The origin, distribution and maintenance of the chromosomal polymorphism found in H. soniae reinforced the hypothesis of the existence of a proto-Y chromosome, demonstrating the rise of an XX/XY sex chromosome system.

Karyotypic and Molecular Analysis of Pterygoplichthys pardalis (Castelnau 1855) from the Lower Amazon River

“…Therefore, it appears that P. pardalis has an intrinsic C-banding polymorphism that is not exclusively associated with genomic adaptation to environmental disturbances. The mechanisms involved in the heterochromatin organization of fish genomes are not completely understood; however, it is clear that heterochromatin accumulation can play a role in sex chromosome evolution [51] and speciation [52].…”

Adding New Pieces to the Puzzle of Karyotype Evolution in Harttia (Siluriformes, Loricariidae): Investigation of Amazonian Species

“…nigrirostrum [ 25 , 26 , 27 ]. Additionally, several types of sex chromosome systems including standard, derived, and multiple ones have been described for Loricariidae, as exemplified by Hypostomus genus with different ZW and XY cases [ 28 , 29 , 30 , 31 ], XX/XY, XX/X0, ZZ/ZW, and Z 1 Z 1 Z 2 Z 2 /Z 1 Z 2 W 1 W 2 in several Ancistrus species (reviewed in ref. [ 32 ]), and three male-heterogametic systems in the genus Harttia (see below).…”