The Ancistrus genus has extensive chromosomal diversity among species, including heteromorphic sex chromosomes occurrence. However, studies have been shown that chromosomal diversity may still be underestimated. Repetitive sequences represent a large part of eukaryotic genomes, associated with mechanisms of karyotypic diversification, including sex chromosomes evolution. This study analyzed the karyotype diversification of two Ancistrus species (Ancistrus sp. 1 and Ancistrus sp. 2) from the Amazon region by classical and molecular chromosomal markers. Conventional chromosome bands and fluorescence in situ hybridization using probes 18S and 5S rDNA, besides (CA)n, (CG)n, (GA)n, (CAC)n, (CAG)n, (CAT)n, (GAA)n, (GAC)n, (TAA)n, and (TTAGGG)n in tandem repeats were determined on the karyotypes. Ancistrus sp. 1 and Ancistrus sp. 2 presented karyotypes with 2n = 38 (20 m + 14sm+4st, XX/XY) and 2n = 34 (20 m + 14sm, without heteromorphic sex chromosomes), respectively. Robertsonian rearrangements can explain the diploid number difference. C-bands occurred in pericentromeric regions in some chromosomes, and a single 18S rDNA locus occurred in both species. The 5S rDNA showed variation in the number of loci between species karyotypes, suggesting the occurrence of unstable sites and rearrangements associated with these sequences in Ancistrus. The microsatellite mapping evidenced distinct patterns of organization between the two analyzed species, occurring mainly in the sex chromosomes in Ancistrus sp. 1, and in the centromeric and pericentromeric regions of chromosomes m/sm in Ancistrus sp. 2. These data shows the extensive chromosomal diversity of repetitive sequences in Ancistrus, which were involved in Robertsonian rearrangements and sex chromosomes differentiation.

Peckoltia is widely distributed genus in the Amazon and Orinoco basins and the Guiana Shield, containing 18 valid species, and distinct morphotypes still needing description in the scientific literature due to its great taxonomic complexity. This study performed a comparative chromosomal analysis of two undescribed Peckoltia species (Peckoltia sp. 3 Jarumã and Peckoltia sp. 4 Caripetuba) from the Brazilian Amazon using conventional chromosome bands methods and in situ localization of the repetitive DNA (5S and 18S rRNA and U1 snRNA genes and telomeric sequences). Both species presented 2n = 52 but differed in their karyotype formula, probably due to inversions or translocations. The nucleolus organizer regions (NORs) showed distal location on a probably homeologous submetacentric pair in both species, besides an extra signal in a subtelocentric chromosome in Peckoltia sp. 4 Caripetuba. Heterochromatin occurred in large blocks, with different distributions in the species. The mapping of the 18S and 5S rDNA, and U1 snDNA showed differences in locations and number of sites. No interstitial telomeric sites were detected using the (TTAGGG)n probes. Despite 2n conservationism in Peckoltia species, the results showed variation in karyotype formulas, chromosomal bands, and locations of repetitive sites, demonstrating great chromosomal diversity. A proposal for Peckoltia karyotype evolution was inferred in this study based on the diversity of location and number of chromosomal markers analyzed. A comparative analysis with other Peckoltia karyotypes described in the literature, their biogeography patterns, and molecular phylogeny led to the hypothesis that the derived karyotype was raised in the left bank of the Amazon River.

Pseudacanthicus is a genus of Neotropical fish with eight valid species, in addition to numerous lineages not formally identified. It occurs along the Amazon and Tocantins River basins, in Suriname and in the Guiana shield. There are no karyotypic data in the literature for species of this genus. Here, the karyotypes of three Pseudacanthicus species (P. spinosus, P. leopardus and Pseudacanthicus sp.) were comparatively analyzed by classical cytogenetics and fluorescence in situ hybridization using 18S and 5S rDNA probes, U2 snDNA and telomeric sequences. The analyzed species presented 52 chromosomes and KF = 18 m + 34 sm. Constitutive heterochromatin occurred in blocks on a few chromosomes. The 18S rDNA occurred in a single pair; interestingly, P. leopardus presented only one locus of this sequence in its diploid genome. The 5S rDNA sequence occurred in only one pair in P. leopardus, and in multiple sites in Pseudacanthicus sp. and P. spinosus. The snDNA U2 occurred in only one pair in all analyzed species. Telomeric sequences did not show interstitial sites. Although Pseudacanthicus species share the same 2n and KF, repetitive sequence analysis revealed karyotypic diversity among these species. The occurrence of DNA double-strand breaks related to fragile sites, unequal crossing over and transpositions is proposed as the mechanism of karyotypic diversification, suggesting that the conservation of the karyotypic macrostructure is only apparent in this group of fish.

Loricariidae é uma das mais especiosas famílias dentro da ordem Siluriformes, possuindo cerca de 800 espécies válidas. O gênero Peckoltia (Loricariidae, Hypostominae), atualmente contém 19 espécies válidas, apresentando status taxonômico confuso. O objetivo deste trabalho foi analisar comparativamente os cariótipos das espécies Peckoltia cf. braueri e Peckoltia sp., coletadas no município Abaetetuba – PA por métodos clássicos (coloração convencional e bandeamento C) e Hibridização in situ Fluorescente com sondas de rDNA 18S, 5S e telomérica. As espécies compartilham o 2n=52 cromossomos, mas diferem nas fórmulas cariotípicas. P. cf. braueri apresentou 20m + 24sm + 8st/a, enquanto P. sp. apresentou 26m + 14sm + 12st/a. O bandeamento C revelou grandes blocos heterocromáticos distribuídos em cromossomos submetacêntricos nas duas espécies. Diferenças da quantidade e distribuição de heterocromatina foram observadas nos cromossomos 24 de P. cf. braueri e 21 de P. sp., sugerindo a ocorrência de rearranjos cromossômicos dos tipos inversão paracêntrica e translocação. As hibridizações com sondas de rDNA 18S e 5S revelaram diferenças na localização e número de sítios entre os cariótipos analisados. Peckoltia cf. braueri apresentou sítios múltiplos de rDNA 5S em posição distal do par 11q e homólogo do par 24q, o rDNA 18S apresentou marcações simples em região distal do par 11q. Peckoltia sp. apresentou sítios simples de rDNA 5S em posição intersticial do par 1p, enquanto o rDNA 18S apresentou sítios múltiplos em região distal do par 11q e homólogo do par 21q. Essas diferenças na distribuição dos genes de rDNA possivelmente está relacionada a dinâmica evolutiva dessas sequências, provavelmente associadas a elementos transponíveis. A hibridização das sondas teloméricas revelaram sítios distais nos cromossomos, nas duas espécies, não sendo evidenciadas sequências intersticiais. Sugerimos que a distribuição de heterocromatina representa um bom marcador para análises evolutivas nas espécies de Peckoltia, podendo ser útil na identificação de rearranjos cromossômicos e de suas consequências na diferenciação cariotípica entre espécies relacionadas. Além disso, o mapeamento de rDNA representa uma ferramenta poderosa para estudo da evolução cromossômica em peixes do gênero Peckoltia.