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

Abstract

Cytogenetic studies in the subfamily Potamotrygoninae have provided valuable insights into the understanding of the evolution and diversification of its species. In the present study, the chromosomal features of seven nominal potamotrygonin species are provided: Plesiotrygon iwamae (2n=74, FN=120), Potamotrygon amazona (2n=66, FN=107), P. constellata (2n=66, FN=110), P. leopoldi (2n=64, FN=102), P. motoro (2n=66, FN=106) from four different localities, and P. orbignyi (2n=66, FN=106), P. scobina (2n=66, FN=104), from Central Amazon. Additionally, we found a new karyomorph in P. wallacei. We considered the localization of Nucleolus Organizer Regions (NORs), as well as the pattern of constitutive heterochromatin, as species-specific characters. We found an XX/XY sex chromosome system in P. orbignyi, and we suggest that P. scobina and P. amazona also possess the same sex chromosome system. Overall, the chromosomal evolution in this group appears to have progressed towards a reduction in diploid number, with a concomitant increase in the number of bi-armed and nucleolar chromosomes.

Cell culture-based karyotyping of orectolobiform sharks 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 44 , 46 . In chondrichthyans, sex chromosomes have been reported for eight species when only those reports based on multiple individuals for both sexes are considered 17 , 26 , 47 – 50 (Fig. 5 and Supplementary Data 1 ).…”

“…However, to our knowledge, no reliable karyotype reports are available for Orectolobiformes. In most past cytogenetic studies of chondrichthyans, chromosome preparations were prepared using in vivo treatment protocols involving the collection of mitotic cells directly from animal tissues in which mitotic inhibitors were injected before sacrifice 17 , 18 . The abundance of chromosomes has been a hurdle in chondrichthyan cytogenetics, but the most crucial obstacle lies in the supply of cultured cells to obtain high-quality chromosome spreads.…”

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).…”

“…Although not included in the eight species whose sex chromosomes were identified, sex chromosomes have been suggested for 13 more elasmobranch species; however, the studies that have documented this have included only one sex or one individual 15,25,45,[50][51][52] (Supplementary Table 1). To avoid such unreliability, the present study included both sexes and multiple individuals per sex of the brownbanded bamboo shark and whitespotted bamboo shark and revealed differentiated X and Y sex chromosomes in these two species (Fig.…”

“…However, to our knowledge, no reliable karyotype reports are available for Orectolobiformes. In most past cytogenetic studies of chondrichthyans, chromosome preparations were prepared using in vivo treatment protocols involving the collection of mitotic cells directly from animal tissues in which mitotic inhibitors were injected before sacrifice 15,16 . The abundance of chromosomes has been a hurdle in chondrichthyan cytogenetics, but the most crucial obstacle lies in the supply of cultured cells.…”