Análises cromossômicas, clássica e molecular, de três espécies de Farlowella Eigenmann & Eigenmann, 1889 (Siluriformes, Loricariidae, Loricariinae)

Abstract

The genus Farlowella is known as catfish or branchfish, of distribution restricted to the rivers of South America, having, in the Amazon basin, groups of endemic species. This genus is characterized by presenting: body covered by bony plates, long and depressed caudal peduncle; prominent snout and absence of adipose fin and because of their peculiar morphology are sold as ornamental fish. However, Farlowella's systematics remains confused and controversial, and has gone through different groupings throughout its history. Thus, the present study aimed to characterize, through classical and molecular cytogenetic analyzes, three Farlowella species that occur in Negro River basin, in order to find possible species-specific markers or population-based markers that allow inferring on the mechanisms of its chromosome evolution. We analyzed 28 individuals of three Farlowella species from different localities: F. cf. amazona from the vicinity of the city of Barcelos-AM, F. oxyrryncha of the Igarapé of Agenor Site and F. schreitmuelleri of Igarapé Jundiá, both located in the Municipality of Manaus-AM. The three species presented 2n = 58 chromosomes and fundamental number 110, 112 and 116 arms. As for constitutive heterochromatin, the three species exhibited blocks in centromeric region and adjacencies, as well as some bitelomeric markers and only F. oxyrryncha and F. schreitmuelleri showed interstitial markings. Furthermore, the C-band pattern observed in pair 27 of F. oxyrryncha appears to characterize a sex chromosome system of type XX/XY. The nucleolar chromosomal pair appears to be homeologous between species. The 5S rDNA probe was a species-specific marker. FISH with telomeric probe detected interstitial telomeric sequences (ITS) in F. oxyrryncha and F. schreitmuelleri and these were matched with heterochromatin. In F. oxyrryncha ITSs was polymorphic, with four variations observed. From the data obtained it was possible to suggest that the chromosomal rearrangements involved in the karyotype evolution of this genus and in the differentiation of sex chromosomes are non Robertsonian rearrangements, and that interspecific and population differences may suggest the presence of species complexes in this genus.