X1X1X2X2/X1X2Y sex chromosome systems in the Neotropical Gymnotiformes electric fish of the genus Brachyhypopomus

Abstract

Several types of sex chromosome systems have been recorded among Gymnotiformes, including male and female heterogamety, simple and multiple sex chromosomes, and different mechanisms of origin and evolution. The X1X1X2X2/X1X2Y systems identified in three species of this order are considered homoplasic for the group. In the genus Brachyhypopomus, only B. gauderio presented this type of system. Herein we describe the karyotypes of Brachyhypopomus pinnicaudatus and B. n. sp. FLAV, which have an X1X1X2X2/X1X2Y sex chromosome system that evolved via fusion between an autosome and the Y chromosome. The morphology of the chromosomes and the meiotic pairing suggest that the sex chromosomes of B. gauderio and B. pinnicaudatus have a common origin, whereas in B . n. sp. FLAV the sex chromosome system evolved independently. However, we cannot discard the possibility of common origin followed by distinct processes of differentiation. The identification of two new karyotypes with an X1X1X2X2/X1X2Y sex chromosome system in Gymnotiformes makes it the most common among the karyotyped species of the group. Comparisons of these karyotypes and the evolutionary history of the taxa indicate independent origins for their sex chromosomes systems. The recurrent emergence of the X1X1X2X2/X1X2Y system may represent sex chromosomes turnover events in Gymnotiformes.

Karyotypic Diversity and Evolution in a Sympatric Assemblage of Neotropical Electric Knifefish

“…The cytogenetic data generated in this study, in combination with previous studies ( Almeida-Toledo et al, 2000 ; Mendes et al, 2012 ; Cardoso et al, 2015a ), reveal interspecific karyotypic divergence for the genus Brachyhypopomus in general, and for the Tefé assemblage in particular ( Table 4 ). These differences are reflected in the diploid number (2 n ), which can result from chromosome fusion/fission events ( Milhomem et al, 2008 ).…”

“…Although several species of Brachyhypopomus share the same 2 n but different KFs, two pairs of sister species share both 2 n and KF: B. bennetti + B. walteri (sympatric in Tefé region) and B. pinnicaudatus + B. gauderio (allopatric). The latter pair also share a putatively homologous multiple sex chromosome system ( Cardoso et al, 2015a ). Despite the apparent karyotypic conservation in these two sister species pairs, there is divergence in the localization of the CH between sister species.…”

“…For example, B. pinnicaudatus (widespread in the Amazon basin) is sister species to B. gauderio (widespread in the Paraná and Patos-Mirim basins of southern South America) ( Crampton et al, 2016b ). Among the species in the Tefé assemblage, cytogenetic data are previously known only for B. pinnicaudatus and B. flavipomus ( Cardoso et al, 2015a ). Additionally, karyotypic information is available for two populations of B. gauderio from the Paraná basin ( Almeida-Toledo et al, 2000 ; Mendes et al, 2012 ).…”

Deciphering the Origin and Evolution of the X1X2Y System in Two Closely-Related Oplegnathus Species (Oplegnathidae and Centrarchiformes)

“…Including Oplegnathus , about 60 cases of multiple sex chromosomes have so far been reported across the teleost phylogeny (reviewed in [13], for more recent examples, see [30,31,32,33,34,35,36,37,38,39]). In this context, molecular cytogenetics provides a powerful toolbox for understanding the genome evolution and organization [40,41,42], and many of these approaches have enabled unique insights into the vertebrate sex chromosome evolution.…”

Computational identification of Y-linked markers and genes in the grass carp genome by using a pool-and-sequence method

“…The two common sex chromosome systems in most species are XX/XY and ZZ/ZW. However, some species present other types, such as XX/XO type in Giant freshwater stingray ( Himantura dalyensis ) 7 , X1X1X2X2/X1X2Y type in Neotropical gymnotiformes electric fish ( Gymnotiformes ) 8 , ZZ/ZW1W2 type in Apareiodon hasemani eigenmann ( Characiformes: Parodontidae ) 9 and so on 10 . Compared with recent vertebrates, fish lack morphologically and genetically differentiated sex chromosomes.…”