Abstract The Neotropical armored catfish genus Harttia presents a wide variation of chromosomal rearrangements among its representatives. Studies indicate that translocation and Robertsonian rearrangements have triggered the karyotype evolution in the genus, including differentiation of sex chromosome systems. However, few studies used powerful tools, such as comparative whole chromosome painting, to clarify this highly diversified scenario. Here, we isolated probes from the X1 (a 5S rDNA carrier) and the X2 (a 45S rDNA carrier) chromosomes of Harttia punctata, which displays an X1X1X2X2/X1X2Y multiple sex chromosome system. Those probes were applied in other Harttia species to evidence homeologous chromosome blocks. The resulting data reinforce that translocation events played a role in the origin of the X1X2Y sex chromosome system in H. punctata. The repositioning of homologous chromosomal blocks carrying rDNA sites among ten Harttia species has also been demonstrated. Anchored to phylogenetic data it was possible to evidence some events of the karyotype diversification of the studied species and to prove an independent origin for the two types of multiple sex chromosomes, XX/XY1Y2 and X1X1X2X2/X1X2Y, that occur in Harttia species. The results point to evolutionary breakpoint regions in the genomes within or adjacent to rDNA sites that were widely reused in Harttia chromosome remodeling.

RESUMO Ancistrus é um gênero rico em espécies de peixes conhecidos como cascudos e tem sido alvo de estudos citogenéticos nos últimos 17 anos. Uma comparação da plasticidade presente no gênero é apresentada com novas análises citogenéticas para Ancistrus cf. multispinis e Ancistrus aguaboensis. Este estudo visa melhorar nossa compreensão da evolução cromossômica associada as alterações do número diploide (2n) e a dispersão de DNAs ribossômicos (rDNAs) em Ancistrus. Ancistrus cf. multispinis e A. aguaboensis apresentaram 2n de 52 e 50 cromossomos, respectivamente. Visto que A. cf. multispinis compartilha 2n = 52 também encontrado em Pterygoplichthyini, o grupo irmão para Ancistrini, um evento de fusão Robertsoniana (Rb) é proposto para a redução do 2n em A. aguaboensis. Sítios de pseudogenes de rDNA 5S já foram associados a eventos de fusão Rb em Ancistrus e nossas análises sugerem que a redução do 2n em A. aguaboensis foi desencadeada por quebras na dupla fita e rearranjos cromossômicos em sítios de rDNA 5S. A presença de evolutionary breakpoint regions (EBRs) em clusters de rDNA foi proposta para explicar parte da fusão Rb em Ancistrus. Os dados citogenéticos apresentados ampliam a diversidade já documentada em Ancistrus visando melhor entender o papel dos rearranjos cromossômicos na diversificação de Ancistrini.

ABSTRACT Ancistrus is a specious genus of armored catfishes that has been extensively used for cytogenetic studies in the last 17 years. A comparison of the extensive karyotypic plasticity within this genus is presented with new cytogenetic analysis for Ancistrus cf. multispinis and Ancistrus aguaboensis. This study aims to improve our understanding of chromosomal evolution associated with changes in the diploid number (2n) and the dispersion of ribosomal DNAs (rDNAs) within Ancistrus. Ancistrus cf. multispinis and A. aguaboensis exhibit 2n of 52 and 50 chromosomes, respectively. Given that A. cf. multispinis shares a 2n = 52 also found in Pterygoplichthyini, the sister group for Ancistrini, a Robertsonian (Rb) fusion event is proposed for the 2n reduction in A. aguaboensis. 5S rDNAs pseudogenes sites have already been associated with Rb fusion in Ancistrus and our analysis suggests that the 2n reduction in A. aguaboensis was triggered by double strand breaks (DSBs) and chromosomal rearrangements at 5S rDNA sites. The presence of evolutionary breakpoint regions (EBRs) into rDNA cluster is proposed to explain part of the Rb fusion in Ancistrus. Cytogenetic data presented extends the diversity already documented in Ancistrus to further understand the role of chromosomal rearrangements in the diversification of Ancistrini.

Abstract Parodontidae is a small group of fish and some species are particularly difficult to identify due to the lack of sufficiently consistent morphological traits. Cytogenetically, the species possess 2n = 54 chromosomes and are either sex-homomorphic or sex-heteromorphic (regarding its chromosomes). We evaluated data on color, tooth morphology, cytogenetics, and mitochondrial markers (COI) in Apareiodon specimens from the Aripuanã River (Amazon basin) and the results were compared to other congeneric taxa. Morphological results show an overlap of body color and tooth morphology to other known Apareiodon. The cytogenetics data showed that the 2n = 54 chromosomes, 50 m/sm + 4 st and, a ZZ/ZW sex chromosome system in Apareiodon sp. are common to other species of the genus. However, the number and chromosomal localization of the 45S ribosomal and pPh2004 satellite DNA sites, in addition to W chromosome localization of the pPh2004 appear to be exclusive cytogenetic features in Apareiodon sp. Our phylogenetic tree revealed well-supported clades and confirmed, by barcode species delimitation analysis, a new Molecular Operational Taxonomic Unit (MOTU) for Apareiodon sp. (Aripuanã River). As a whole, the above features support the occurrence of a new species of the Apareiodon, thus far unknown for the Parodontidae.