Análise citogenética de Pseudoloricaria laeviuscula (Valenciennes, 1840) (Loricariidae, Loricariinae, subtribo Loricariina):Um gênero monotípico

Abstract

Pseudoloricaria is a genus considered monotypic, which underwent some taxonomic reallocations throughout its discovery, and existing studies are scarce, predominantly based on morphological criteria. The present study investigated the species Pseudoloricaria laevisucula collected in the Cuieiras River and Anavilhanas National Park, Rio Negro, both locations in Amazonas, Brazil, using conventional and molecular cytogenetic procedures. The species had a diploid number of 54 chromosomes, with a karyotype composed of 14 metacentric, 10 submetacentric, 4 subtelocentric and 26 acrocentric (14m + 10sm + 4st + 26a), and a Fundamental Number (NF) equal to 82. The Organizing Regions of Nuclei (NORs) are in a subtelocentric, interstitial chromosome pair, while heterochromatic blocks were scarce and predominantly pericentromeric. The 18S rDNA markings confirmed Ag-RON, the 5S rDNA showed pericentromeric marking in a single acrocentric chromosomal pair and the telomeric probes marked only the chromosomal ends. P. laeviuscula revealed characteristics considered plesiomorphic within the Loricariidae family, in relation to diploid number, NORs and constitutive heterochromatin. However, for the mapping of 18S and 5S ribosomal DNAs, the species did not show synteny, which for the family is a derived character. The cytogenetic data indicated the occurrence of non-Robertsonian rearrangements such as inversions, a pattern previously observed in species of the Loricariichthys group, of which P. laeviuscula is part within the Loricariinae. This study expanded knowledge about the genus, contributing with cytogenetic data for the only species described to date and suggests further investigations, looking for other situations in different basins, to elucidate the true monotypy of the genus and dispel taxonomic uncertainties in the group.