Caracterização e Mapeamento Cromossômico de Elementos Repetitivos em Espécies de Rineloricaria (Siluriformes: Loricariidae: Loricariinae).

Abstract

Loricariidae is the most species-rich family among Siluriformes. These fishes are easily recognized due to their body-shape that is covered with bony plates and due to their mouth, which is shaped like a suction cup and located ventrally. It is divided into six subfamilies, with Loricariinae housing the fishes known as “acaris-cachimbo” or “cascudos-chinelo”, widely distributed in South American rivers, occurring from the mouth of the La Plata River, in Argentina, to the coastal rivers of Pacific and Caribbean drainages in Costa Rica. In this study, we analyzed five species of the genus Rineloricaria: R. teffeana (Steindachner 1879), collected in the Tefé River; R. castroi Isbrücker and Nijssen 1984, in the Solimões River; R. lanceolata (Günther 1868), in the Tocantins River; R. fallax (Steindachner 1915) obtained in the aquarium trade and a species not yet described, here designated as Rineloricaria sp. 1, collected in the Purus River, using conventional and molecular cytogenetic techniques. Rineloricaria is a genus that presents huge taxonomic and chromosomal diversity, revealed by different diploid numbers, karyotypic structures and sex chromosome systems. R. teffeana, endemic to northern Brazil, presented 2n = 33♂/34♀, R. fallax presented 2n = 28♀/29♂, R. lanceolata 2n = 48♀♂, Rineloricaria sp. 1 2n = 53♂/54♀ and R. castroi 2n = 58♀♂. Furthermore, the different 2n between the sexes of R. teffeana, R. fallax and Rineloricaria sp. 1 indicates the presence of multiple sex chromosome systems, ♀X1X1X2X2/♂X1X2Y, ♀XX/♂XY1Y2 and ♀X1X1X2X2/♂X1X2Y, respectively. Its origins are hypothesized to be due to different chromosomal rearrangements. C-banding revealed few constitutive heterochromatin, confined pericentromerically in most chromosomes, but also occupying the distal regions of some chromosome pairs, in all species. The chromosomal location of the 18S rDNA sites was conserved, with simple sites in all species analyzed. Already, 5S rDNA revealed simple sites in R. fallax, R. lanceolata and Rineloricaria sp. 1 and multiple sites in R. teffeana and Rineloricaria castroi. Both 5S and 18S rDNAs were colocalized with heterochromatin blocks. The telomeric repeat motif (TTAGGG)n did not show ITS, only markings at the ends of all chromosomes, with the exception of R. teffeana, which showed distinct signal intensity. Our data confirm the general evolutionary trend found in Rineloricaria, with a wide variation in the number of chromosomes, including sex chromosome systems, reinforcing the proposition that chromosomal rearrangements, both Robertsonian and non-Robertsonian, are the main karyoevolutionary mechanisms in this genus, making it an excellent model for evolutionary and biogeographic studies.