Characterization and description of a multiple sex chromosome system in Potamotrygon motoro (Chondrichthyes, Myliobatiformes) from the Paraná River, Argentina

Abstract

ABSTRACT. The Potamotrygonidae family represents the only freshwater group of specialized elasmobranchs and is composed of 4 genera: Plesiotrygon, Paratrygon, Potamotrygon, and Heliotrygon. Individuals of Potamotrygon motoro were collected from the Paraná River at Ituzaingó (Province of Corrientes) in Argentina. Mitotic preparations were obtained using direct techniques and lymphocyte cultures. Chromosomes were studied with conventional Giemsa, C-band and nucleolus organizer region stainings. The diploid number and karyotype formulae were 2n = 66 with 33 homomorphic pairs (14M + 16SM + 22ST + 14A) in females and 2n = 65 with 31 homomorphic pairs plus 3 heteromorphic chromosomes (13M + 15SM + 23ST + 14A) in males. Heterochromatin was distributed at ©FUNPEC-RP www.funpecrp.com.br Genetics and Molecular Research 12 (3): 2368-2375 (2013) Sexual chromosome system in Potamotrygon motoro 2369 the pericentromeric regions of almost all chromosomes and in the telomeric and interstitial positions of some chromosomes. nucleolus organizer regions were multiple and located at telomeric regions. Because of the clear karyotype differences between the 2 sexes and the presence of 3 unpaired chromosomes in males, it is possible to suggest the occurrence of a multiple sex chromosome system, with male heterogamety (X 1 X 1 X 2 X 2 /X 1 X 2 Y). Further cytogenetic studies are required to develop a hypothesis about the origin of the multiple sex chromosome system in P. motoro.

Chromosomal characterization of Amazonian freshwater stingrays with evidence for new karyomorphs and XX/XY sex chromosomes

“…The third, in P. aff. motoro and P. falkneri (Cruz et al , 2011) and in P. motoro (Aichino et al , 2013). Presently, the simple sex-determination systems were found in rays from the Amazon basin (Valentim et al , 2006; 2013; present study), whereas the multiple sex-determination system was found in rays from the Paraná basin (Cruz et al , 2011; Aichino et al , 2013).…”

“…In both freshwater and marine Batoidea, the constitutive heterochromatin was invariably located in the centromeric region of all the chromosomes, and the NORs were multiple (Stingo et al , 1995; Rocco et al , 2002; 2005; 2007; Valentim et al , 2006; 2013; Cruz et al , 2011; Aichino et al , 2013). This pattern was also found in the present study, although individuals of P. motoro from one locality (Jauaperi River) presented terminal heterochromatic blocks on the long arms of a single chromosome pair.…”

“…To date, only six out of 35 species of Neotropical freshwater stingrays have been cytogenetically studied. However, the level of karyotypic variation detected showed distinct diploid numbers, karyotype formulas, and sex chromosomal systems, which represents an essential source of variation that can be used as markers for the characterization of evolutionary processes within different potamotrygonins (Valentim et al , 2006; 2013; 2014; Cruz et al , 2011; 2015; Aichino et al , 2013).…”

Cell culture-based shark karyotyping as a resource for chromosome-scale genome analysis

“…It is widely thought that the sex of chondrichthyans is also determined by the GSD system with XX/XY sex chromosomes 43,45 . In chondrichthyans, sex chromosomes have been reported for eight species when only those reports based on multiple individuals for both sexes are considered 15,25,[46][47][48][49] (Fig. 5, Supplementary Table 1).…”

“…Considering all existing information and our data, we conclude that chondrichthyan karyotypes are generally characterized by numerous chromosomes (up to 106), with a large distribution of chromosome lengths in a karyotype, and sometimes include heteromorphic sex chromosomes. Most chondrichthyan species remain to be analysed, but this emerging karyotypic format is distinct from that of teleost fishes with relatively constant numbers (44)(45)(46)(47)(48)(49)(50)(51)(52)(53)(54) of chromosomes that often include homomorphic sex chromosomes 13,44 . The karyotype provides information about a species' inherent chromosome number and sizes, as well as centromere positions, and provides an ultimate goal of whole-genome sequence reconstruction.…”