The Persevering Cytotaxonomy: Discovery of a Unique XX/XY Sex Chromosome System in Catfishes Suggests the Existence of a New, Endemic and Rare Species

Abstract

The genus Hypostomus has a broad geographic distribution in Brazilian rivers and comprises armored catfishes with a very complicated taxonomy due to the absence of morphological autapomorphies. The existence of nearly 10 allopatric populations with different karyotypes suggests that Hypostomusancistroides represents a species complex in the Upper Paraná River basin. In this paper, an unusual karyotype of an isolated H. aff. ancistroides population was investigated. All specimens of this sample have 2n = 66 chromosomes except for 1 male with 2n = 67, most likely due to a supernumerary chromosome. In this population, the sexes are dimorphic, the males are heterogametic, and an XX/XY sex chromosome system is present. Phylogenetic analysis using mitochondrial and nuclear DNAs indicated that this population forms a monophyletic group separate from the other populations of H.ancistroides and may represent an incipient species.

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

“…The proto-Y chromosome in the genome of H. soniae is larger than the X chromosome, as observed in the Y chromosome of H. aff. ancistroides analyzed by Rocha-Reis et al (2018). Thus, the larger size of the proto-Y chromosome may be the result of the apparent accumulation of heterochromatin, mediated by transposable elements, which may play an important role in the differentiation process, as observed in other species of fish (see Chalopin et al 2015).…”

“…The proto-sex chromosomes of H. soniae were also characterized by the presence of 18S rDNA cistrons. The association between the 18S rDNA sites and sex chromosomes has been reported in fishes (Artoni and Bertollo 2002, Chen et al 2008; Cioffi and Bertollo 2010), including in the genus Hypostomus (Rocha-Reis et al 2018). Repetitive sequences have been recorded at high frequencies in heterochromatic sex chromosomes and Chalopin et al (2015) linked the evolution and emergence of sex chromosomes to the dynamics of the repeats and transposable elements.…”

“…Differentiated sex chromosome systems are not very common in the loricariid catfishes, although simple (Alves et al 2006; de Oliveira et al 2007; Prizon et al 2017) and multiple systems (Centofante et al 2006; de Oliveira et al 2008; Blanco et al 2014) have been described in this family. In the genus Hypostomus , only a simple sexual chromosomal system has been described, with a XX/XY system being found in H. ancistroides and H. macrops , identified as Plecostomus ancistroides and P. macrops , respectively (Michele et al 1977; Rocha-Reis et al 2018), and a ZZ/ZW system in Hypostomus sp. G (Artoni et al 1998), H. cf. plecostomus (Oliveira et al 2015) and H. ancistroides (Kamei et al 2017).…”

EVOLUTIONARY TRENDS IN SPECIES COMPLEX DIAGNOSED BY CYTOGENETIC POLYMORPHISM: THE CASE OFHypostomus ancistroides(SILURIFORMES, LORICARIIDAE)

“…Almost all living organisms possess some karyotype plasticity, although, in certain groups, large plasticity can be considered a characteristic biological trait. This is the case in several groups of fish, especially in the tetras of the genus Astyanax (Characiformes) and in the Hypostomus (Siluriformes) plecos, which may have led to the chromosomal radiation present in these groups (for a review see Pazza and Kavalco 2007;Rocha-Reis, et al 2018). This was also observed in species of Chromaphyosemion (Cyprinodontiformes), especially in C. riggenbachi (Völker et al 2006).…”

“…Although variable when observing the totality of the karyotype macrostructure, the presence of C-banding in some chromosomes of all karyomorphs may indicate the existence of some homology (Rubert et al 2011;Fernandes et al 2012;Maurutto et al 2012;Pansonato-Alves et al 2013;Traldi et al 2013;Lara-Kamei et al 2017;Rocha-Reis et al 2018), and may even be considered a phylogenetic sign. In this study, we observed the presence of conserved C+ blocks in pairs of chromosomes 4 (m), 7 (sm) and 26 (a), in a pericentromeric or subterminal region (Figures 2 and 4).…”