Different cytotypes in fishes of the genus Hypostomus Lcépède, 1803, (Siluriformes: Loricariidae) from Xingu river (Amazon region, Brazil)

• Main Authors: Susana Milhomem, Roberta Castro, C Nagamachi, A De Souza, E Feldberg, Julio Pieczarka
• Format: Article
• Language: English
• Published: Pensoft Publishers 2010-07-01
• Series: Comparative Cytogenetics
• Online Access: http://compcytogen.pensoft.net/lib/ajax_srv/article_elements_srv.php?action=download_pdf&item_id=1692
• ISSN: 1993-0771; 1993-078X

We analyzed the karyotypes of three specimens of fishes of the genus Hypostomus Lacepede, 1803 (Loricaridae) from Xingu River (Amazon region). We used conventional staining techniques, including C-banding, Ag-NOR staining, CMA3- and DAPI-banding. Each specimen had a different cytotype: Hypostomus sp. Xingu-1 had 2n=64 (32M/SM, 32ST/A); Hypostomus sp. Xingu-2 has 2n=66 (32M/SM, 34ST/A), and Hypostomus sp. Xingu-3 had 2n=65 (38M/SM, 26ST/A + 1 B). The three cytotypes showed similar C-, CMA3- and DAPI-banding patterns. The nucleolus organizing regions were located in the short arm of chromosome pair 25 of Hypostomus sp. Xingu-1 and pair 29 of Hypostomus sp. Xingu-2, and in the long arm of pair 30 of Hypostomus sp. Xingu-3, probably because of a pericentric inversion. A fusion/fission rearrangement explains the difference in the diploid number and number of M/SM and ST/A chromosomes between the 2n= 64 and 2n=66 cytotypes. The B chromosome most probably explains the difference between the 2n=64 and 2n=65 cytotypes. The cytotype with 2n=65 had a significantly larger number of M/SM chromosomes, probably because of pericentric inversions. These three cytotypes may represent different species.