Most species of the genus Harttia inhabits the headwaters of small tributaries, but some species are restricted to the main channel of some rivers. This feature, combined with limited dispersal ability, leads to the formation of small isolated populations with reduced gene flow. Currently, there are 23 taxonomically defined and recognized species, and 17 of these are found in Brazil, distributed in several hydrographic basins. Despite this diversity, few chromosomal data for the species belonging to this genus are found in the literature. Thus, this study analyzed, by classical and molecular cytogenetics methodologies, the chromosomal diversity of this genus, to discuss the processes that are involved in the evolution and karyotype differentiation of the species of the group. Seven species of Harttia were analyzed: H. kronei, H. longipinna, H. gracilis, H. punctata, H. loricariformis, H. torrenticola, and H. carvalhoi. The chromosomal diversity found in these species includes different diploid and fundamental numbers, distinct distribution of several repetitive sequences, the presence of supernumerary chromosomes in H. longipinna and multiple sex chromosome systems of the type XX/XYY in H. carvalhoi and XXXX/XXY in H. punctata. Lastly, our data highlight the genus Harttia as an excellent model for evolutionary studies.

Harttia is a genus in the subfamily Loricariinae that accommodates fishes popularly known as armored catfishes. They show extensive karyotypic diversity regarding interspecific numerical/structural variation of the karyotypes, with the presence of the XX/XY1Y2 multiple sex chromosome system, as found in H. carvalhoi. In this context, this study aimed to characterize Harttia punctata chromosomally, for the first time, and to infer the rearrangements that originated the X1X1X2X2/X1X2Y multiple sex chromosome system present in this species. The data obtained in this study, with classical (Giemsa, C-banding and AgNORs) and molecular methodologies (fluorescence in situ hybridization) and chromosome microdissection, indicated that a translocation between distinct acrocentric chromosomes bearing rRNA genes, accompanied by deletions in both chromosomes, might have originated the neo-Y chromosome in this species. The data also suggest that the multiple sex chromosome systems present in H. carvalhoi and H. punctata had an independent origin, evidencing the recurrence of chromosome alterations in species from this genus.

ABSTRACT. We examined chromosomes of three species of the genus Hypostomus, in order to contribute to the understanding of the karyotype evolution of this group. Specimens of H. ancistroides and H. nigromaculatus displayed differences in karyotype formulas, distribution and location of heterochromatin and nucleolus organizer regions when compared to other populations of the same species. We made the first cytogenetic characterization of H. tapijara, an endemic species in the Ribeira de Iguape River. These specimens had 2n = 66 chromosomes, while H. ancistroides showed 2n = 68 and H. nigromaculatus 2n = 76 chromosomes. Physical mapping of 18S and 5S rDNA sites of the three species showed simple, multiple and syntenic clusters. Synteny of ribosomal sites was found in H. ancistroides and H. tapijara, and an interspersed pattern between these sites in all chromosomes bearing the synteny was observed. We conclude that the genus Hypostomus has a high chromosome complexity that is accompanied by great morphological variation. It is evident that this group comprises an interesting model for understanding the chromosome evolution of Neotropical ichthyofauna.

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In this study, which is the first karyotype analysis of Hypostomus iheringii, nine specimens collected in Córrego da Lapa (tributary of the Passa-Cinco River) showed a diploid number of 80 chromosomes. Silver nitrate staining and fluorescence in situ hybridization (FISH) with an 18S rDNA probe revealed the presence of multiple nucleolus organizer regions (NORs) (chromosome pairs 13, 20, and 34). FISH with a 5S rDNA probe showed that this cistron was only present in chromosome pair 2. When the karyotypes of individual animals were compared, unique heterochromatic polymorphisms were detected on chromosome pairs 1 and 5. Specifically, specimens had heterochromatic blocks (h+h+) on both chromosomes, one chromosome with heterochromatic blocks (h+h-) or chromosomes that lacked heterochromatic blocks (h-h-). Considering that heteromorphic pattern is not correlated with variation in size, the process of heterochromatinization might act on the long arms of these chromosomes. In summary, all chromosomal markers indicate that the karyotype of Hypostomus iheringii is highly differentiated and that the heterochromatinization of chromosomal segments may have contributed to its karyotypic differentiation.

Among the more than 30 families of the order Siluriformes, Heptapteridae is composed of 189 species distributed into 24 genera. Rhamdia, which has wide distribution throughout the Neotropical region, presents only 11 valid species, with 8 being in the Brazilian territory. Rhamdia quelen is the only species considered as widely distributed in almost all Brazilian hydrographic basins. It is a Neotropical fi sh species with a confusing taxonomical history. Classic and molecular cytogenetics data for three populations of this species from two large Brazilian hydrographic basins (Paraná and Araguaia) are presented here. The diploid number found for the three analyzed populations was 58 chromosomes, but with distinct karyotypic formulae. The presence of B chromosomes was detected in the two Araguaia River populations with intra-and interindividual variation. C-banding evidenced little heterochromatin in the three analyzed populations. FISH with 18S rDNA probes evidenced a single chromosome pair bearing this site, confi rming the presence of simple NORs, as visualized through silver nitrate staining. The site of 5S rDNA was observed in only one pair of chromosomes, but differing in the marked pair and their location. Based in the differences of the karyotypic formulae and rDNA 5S found between populations on this study and many others available in the literature, it is suggested that this group represents a species complex, and that a new and detailed taxonomical review is necessary.

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.

The B chromosomes are accessory elements that are widely distributed among eukaryotic genomes and often show non-Mendelian inheritance. They are considered dispensable for the growth, development, and reproduction of organisms. Some studies have suggested that these elements may affect sex determination. Harttia is a small armored catfish genus that shows sexual dimorphism, including hypertrophied odontodes on the pectoral fin spines and along the margins of the snout in mature males. They exhibit considerable karyotypic diversity with diploid number (2n) variation and heteromorphic sex system in H. carvalhoi. To date, no occurrences of B chromosomes in the Harttia genus were detected and no relation to sexual differentiation in Neotropical fish has been determined. To determine the validity of this claim, the present paper characterized specimens of Harttia longipinna by classical and molecular cytogenetic methods. The 2n found was 58 (16m + 12sm + 16st + 14a), but of the 50 specimens analyzed (30 male and 20 female), 23 specimens (16 males and seven females) show an intra-individual from 0 to 2 micro B chromosomes. The B chromosomes were completely heterochromatic. The single NORs were shown in the first acrocentric pair with silver staining and 18S rDNA probing. FISH performed with 5S rDNA probe showed a single cistron in the proximal region of the short arm of a small metacentric pair. Thus, the cytogenetic data obtained in this study of H. longipinna highlight the karyotypic diversity found within the genus Harttia, and represent the first description of B chromosomes for this genus.