Chromosome analyses in species of Pareiorhina (Siluriformes, Loricariidae) and cytotaxonomic considerations on the group

摘要

The genus Pareiorhina, formerly considered monotypic, was recently described to comprise two new species P. carrancas and P. brachyrhyncha. Karyotype analysis allowed to infer cytotaxonomical diagnostic characters for P. rudolphi and P. brachyrhyncha in the present study. The species showed the same diploid number (2n = 54) and karyotypes with 18 m, 32sm, 4st and 18 m, 30sm, 6st chromosomes, respectively. In addition, we found that the nucleolus organizer regions (NORs) are located on different chromosomes. Localization of NORs has been ascertained by fluorescent in situ hybridization (FISH) and colloidal silver nitrate stain (Ag-NORs). P. rudolphi shows NORs in interstitial position of the long arm of chromosome pair number 11, while P. brachyrhyncha shows subterminal NORs only in the short arm of chromosome pair 25. Occurrence of diploid chromosome number and presence of only one pair of NOR bearing chromosomes makes these species to comprised of most plesiomorphic karyotype of Loricariidae and supports its clustering with the genus Neoplecostomus. The chromosome types and diversification in the location of NORs corroborate the description of the species P. brachyrhyncha.