Over the last two decades, several classification changes were proposed for the family Loricariidae and their phylogenetic relationships could be only partly resolved so far. Two major problematic groups are the subfamilies Hypoptopomatinae and Neoplecostominae. Therefore, we analysed four species of this family, being three Neoplecostominae (Neoplecostomus yapo, Kronichthys lacerta and Isbrueckerichthys duseni), and one Hypoptopomatinae representative (Parotocinclus maculicauda), in order to compare the chromosomal data to other Loricariidae subfamilies and to the outgroup Trichomycterus sp. To accomplish that, conventional (diploid numbers, karyotype formulae, fundamental number and Ag-NORs -nucleolar organizer regions) and molecular chromosomal markers (dual color FISH -fluorescence in situ hybridization -with 18S and 5S rDNA probes) were used. A similar karyotype structure was reported amongst the studied species. Inferences about putative plesiomorphic chromosomal markers were established and/or corroborated in Loricariidae, such as: 2n = 54 chromosomes, small amounts of heterochromatin, a single NOR-bearing pair and synteny 18S and 5S rDNA at interstitial region. Thus, the present chromosomal analysis hypothesizes primitive chromosomal characters and contributes to a better understanding of chromosomal evolutionary processes among loricariids.
The family Parodontidae presents a conserved diploid number of 54 chromosomes and different stages associated with ZW sex chromosome differentiation. For the great majority of species in this family it was proposed that the karyotypic diversification is mostly due to repetitive DNA mobility and accumulation. In this study, 2 repetitive probes, (GATA)n and (TTAGGG)n, were used to assess probable mechanisms of chromosome diversification, especially those related to molecular differentiation of the W chromosome. Results showed that the (GATA)n sequence is involved in the differentiation of the W chromosome female-specific region of Parodontidae and that it is accumulated in diverse autosomes. The (TTAGGG)n repeat is part of the vertebrate telomere, and the presence of interstitial telomeric sites may help to identify chromosome rearrangements. However, in Parodontidae, no interstitial telomeric sites were detected. This study shows plasticity in the amount of the (GATA)n repeat in Parodontidae that may be involved in chromatin modifications and transcriptional control of the W chromosome, and the role of repetitive DNAs in genomic diversification in this fish family is discussed.
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