Karyotypic conservatism in five species of Prochilodus (Characiformes, Prochilodontidae) disclosed by cytogenetic markers

ANIMAL GENETICS

RESEARCH ARTICLE

Karyotypic conservatism in five species of Prochilodus (Characiformes, Prochilodontidae) disclosed by cytogenetic markers

Tatiana Aparecida Voltolin^I; Manolo Penitente^I; Bruna Bueno Mendonça^I; José Augusto Senhorini^III; Fausto Foresti^II; Fábio Porto-Foresti^I

^IDepartamento Ciências Biológicas, Faculdade de Ciências, Universidade Estadual Paulista "Julio de Mesquita Filho", Bauru, SP, Brazil

^IIDepartamento de Morfologia, Instituto de Biociências, Universidade Estadual Paulista "Julio de Mesquita Filho", Botucatu, SP, Brazil

^IIIInstituto Chico Mendes de Conservação da Biodiversidade, Centro Nacional de Pesquisa e Conservação de Peixes Continentais, Pirassununga, SP, Brazil

^{Send correspondence to}

ABSTRACT

The family Prochilodontidae is considered a group with well conserved chromosomes characterized by their number, morphology and banding patterns. Thence, our study aimed at accomplishing a cytogenetic analysis with conventional methods (Giemsa staining, silver staining of the nucleolus organizer regions-AgNOR, and C-banding) and fluorescence in situ hybridization (FISH) with 18S and 5S ribosomal DNA probes in five species of the Prochilodus genus (Prochilodus argenteus, Prochilodus brevis, Prochilodus costatus, Prochilodus lineatus and Prochilodus nigricans) collected from different Brazilian hydrographic basins. The results revealed conservatism in chromosome number, morphology, AgNORs 18S and 5S rDNAs location and constitutive heterochromatin distribution patterns. The minor differences observed in this work, such as an Ag-NOR on a P. argenteus chromosome and a distinct C-banding pattern in P. lineatus, are not sufficient to question the conservatism described for this group. Future work using repetitive DNA sequences as probes for FISH will be interesting to further test the cytogenetic conservatism in Prochilodus.

Keywords: AgNOR, C-banding, hydrographic basins, conserved karyotype, FISH.

Introduction

Fishes of the family Prochilodontidae are significant components of the fauna of Neotropical rivers and are considered one of the most important elements of commercial and subsistence freshwater fisheries in South American environments, except in Chile, where they are not found (Lowe-McConnell, 1975; Goulding, 1981; Vari, 1983; Flecker, 1996).

Cytogenetic data on Prochilodus species revealed a conserved karyotype with 2n = 54 chromosomes and a fundamental number FN = 108 (Pauls and Bertollo, 1983, 1990), suggesting that the family Prochilodontidae exhibits a predominantly conserved chromosomal evolution (Pauls and Bertollo, 1990). However, a few populations and/or, species, such as P. brevis, P. lineatus, P. mariae and P. nigricans, showed karyotypic variation due to the presence of supernumerary chromosomes (Pauls and Bertollo 1983, 1990; Oliveira et al., 1997, 2003; Dias et al., 1998; Venere et al., 1999; Maistro et al., 2000; Cavallaro et al., 2000; Jesus and Moreira-Filho, 2003; Artoni et al., 2006; Voltolin et al., 2009).

Conventional cytogenetic markers, such Ag-NORs, evidenced a single chromosome pair bearing NORs in some species of Prochilodus (Pauls and Bertollo, 1990; Venere et al., 1999; Oliveira et al., 2003; Jesus and Mo-reira-Filho, 2003; Vicari et al., 2006; Voltolin et al., 2009).

Data on the localization of the 5S and 18S ribosomal genes by FISH in the genomes of species of Prochilodontidae are still scarce (Jesus and Moreira-Filho, 2003; Hatanaka and Galetti Jr, 2004; Vicari et al., 2006; Grass et al., 2007; Terêncio et al., 2012). FISH with the 5S and 18S ribosomal genes showed that they are syntenic in P. lineatus and P. argenteus, and evidenced a polymorphism in the number of 18S rRNA genes (Jesus and Mo-reira-Filho, 2003; Hatanaka and Galetti Jr, 2004; Voltolin et al., 2009).

C-banding analyses carried out in Prochilodontidade representatives showed that the constitutive heterochromatin is frequently restricted to centromeric blocks in all chromosomes of the standard (A) complement (Pauls and Bertollo, 1990; Venere et al., 1999; Cavallaro et al., 2000; Oliveira et al., 2003; Jesus and Moreira-Filho 2003; Artoni et al., 2006; Voltolin et al., 2009). Additionally, the supernumerary chromosomes were usually entirely heterochromatic in these species (Pauls and Bertollo 1990; Maistro et al., 2000; Cavallaro et al., 2000; Jesus and Moreira-Filho, 2003; Artoni et al., 2006; Voltolin et al., 2009).

Therefore, the objective of the current study was to conduct a comparative analysis with conventional and molecular cytogenetic markers in five species of the genus Prochilodus collected in different Brazilian hydrographic basins to look for chromosome differences that may have accumulated in these populations over the years allowing their cytogenetic differentiation.

Materials and Methods

We analyzed 20 samples of P. lineatus from the Mogi-Guaçu river, Pirassununga, (São Paulo); 17 individuals of P. nigricans from the Tocantins Araguaia basin (Tocantins); 15 individuals of P. costatus acquired from the Aquicultura Tropical pisciculture, Propiá (Sergipe); six samples of P. argenteus from the São Francisco basin; and five individuals of P. brevis, acquired from the Departamento de Nacional de Obras Contra a Seca (DNOCS) dam, in Natal (Rio Grande do Norte).

Mitotic chromosomes were obtained from anterior kidney fragments (Foresti et al., 1981) and through lymphocyte culture (Fenocchio and Bertollo.,1988) with some adjustments. The karyotypes were arranged according to Levan et al. (1964).

Active NORs were identified after silver nitrate staining (Howell and Black, 1980) and the constitutive heterochromatin was detected after C-banding (Sumner, 1972).

FISH was carried out according to Pinkel et al. (1986) using 5S rDNA probes obtained by PCR from Prochilodus genomic DNA using the primers A (5_-TACGCCCGATCTCG TCCGATC-3_) and B (5_-CAGGCTGGTATGGCCGTAAGC-3_) (Pendás et al., 1994). The 18S rDNA probe was obtained by PCR using the NS1 (5_-GTAGTCATATGCTTGTCTC-3_) and NS8 (5_-TCCGCAGGTTCACCTACGGA-3_) primers (White et al., 1990).

The 5S probe was labeled with biotin-dUTP and the 18S probe was labeled with digoxigenin-dUTP (Roche) by PCR, according to the manufacturer's instructions.

The 5S and 18S rDNA probes were denatured in 70% formamide:2xSSC for 5 min. The hybridization occurred at 37 ºC overnight in a moist chamber (0.3 !g of denatured probe, 50% formamide, 10 mg/mL of dextran sulfate; 2xSSC, 5 mg/mL of salmon sperm DNA).

The 5S and 18S probes were immunodetected with avidin-FITC and anti-digoxigenin-rhodamine, respectively, and the preparations were counterstained with DAPI (4-6-diamidino-2-phenylindole) and examined under an epifluorescence photomicroscope (BX 61, Olympus) equipped with an Olympus DP70 cooled digital camera. Photomicrographs were taken using the Pro MC 6.0 software.

Results

All specimens of Prochilodus (P. argenteus, P. brevis, P. costatus, P. lineatus and P. nigricans) collected in the different Brazilian hydrographic basins presented a karyotype with 2n = 54, FN = 108 and metacentric and submetacentric chromosomes (Figure 1a-e). All specimens of P. lineatus had supernumerary chromosomes (Figure 2a), whereas one P. nigricans specimen had a single B chromosome that showed intraindividual variation, with 23 cells out of 30 exhibiting the extra chromosome (Figure 2b).

After Ag-NOR staining, only one homolog of a submetacentric pair presented a NOR in P. brevis, P. costatus, P. lineatus and P. nigricans (Figure 1b-e, highlighted). In P. argenteus, the NOR was observed only on one homologue of the second largest submetacentric pair. This Ag-NORs pattern was found in approximately 40 metaphases of all P. argenteus specimens.

FISH with the 5S and 18S rDNA probes was performed to confirm if there was a karyotypic difference in the 18S gene location in P. argenteus. Synteny between these two genes was observed in all samples tested, including P. argenteus, in which the 18S rDNA labeled both homologues of the second submetacentric pair, which was not observed after Ag-NOR (Figure 3a, b, c, d and e). Furthermore, the location of these genes was identical in all the species, i.e., the 5S gene was located near the terminal region of the long arm of the submetacentric chromosome pair and the 18S gene, in a pericentromeric position, syntenic with the 5S gene. Clusters of these ribosomal sequences were not detected in any of the species studied, nor in the B chromosomes present in the genome of P. lineatus and P. nigricans.

C-banding was performed to identify the distribution of constitutive heterochromatin in all the species. The results allowed us to differentiate among the specimens of P. lineatus and those of the other four Prochilodus species. Conspicuous heterochromatic blocks present only in the centromeric regions of the standard A chromosome set were observed in P. lineatus (Figure 4d). In P. argenteus, P. brevis, P. costatus and P. nigricans, besides the presence of heterochromatic regions in the centromere, a large heterochromatic block on the long arm of a submetacentric chromosome pair was also observed (Fig. 4b-e). The supernumerary chromosomes of P. lineatus and P. nigricans were totally heterochromatic (Figure 4d, e).

Discussion

Pioneer studies in Prochilodus cytogenetics conducted by Pauls and Bertollo (1983, 1990) evidenced a con-spicuous homogeneity in karyotypes. Several studies have shown that specimens of Prochilodus presented 2n = 54, FN = 108 and biarmed chromosomes (Pauls and Bertollo, 1983, 1990; Oliveira et al., 1997; Cavallaro et al., 2000, Jesus and Moreira-Filho, 2003; Voltolin et al., 2009). Our results are consistent with these data (Figure 1a-e).

The presence of supernumerary microchromosomes in some species of Prochilodus enabled us to study aspects concerning their origin, evolution, structure and maintenance. First described in P. lineatus by Pauls and Bertollo (1983), up to two B microchromosomes were also identified in P. brevis (=P. cearensis) by these same authors (Pauls and Bertollo (1990). Venere et al. (1999) described the occurrence of one or two B chromosomes in P. nigricans and Oliveira et al. (2003) identified up to three supernumerary chromosomes in some individuals of P. mariae from the Orinoco river basin in Venezuela.

The specimens of P. brevis, P. costatus, P. lineatus and P. nigricans studied herein had only one Ag-NOR situated on the long arm of the second largest submetacentric pair (inbox in Figure 1b-e), as already described for these species (Pauls and Bertollo, 1983.1990; Venere et al., 1999; Maistro et al., 2000; Jesus and Moreira-Filho, 2003; Hatanaka and Galetti Jr, 2004; Vicari et al., 2006; Artoni et al., 2006; Voltolin et al., 2009).

In P. argenteus, a single AgNOR was observed on the long arm of one homologue of a submetacentric chromosome (inbox in Figure 1a). This result is inconsistent with the literature data for this species, in which the single AgNOR was observed on the second largest submetacentric pair (Hatanaka and Galetti Jr, 2004).

Silver nitrate does not directly bind to rDNA, but to the proteins associated with the nucleolar structure, restricting the identification to the NORs that had been active in the preceding interphase (Miller et al., 1976). This is the most reasonable hypothesis to explain the single AgNOR in P. argenteus.

The position of the ribosomal genes was further investigated with FISH with the 18S and 5S rDNA probes.

These probes were syntenic in agreement with previous reports (Jesus and Moreira-Filho, 2003;, Hatanaka and Galetti Jr, 2004; Vicari et al., 2006). No additional18S clusters were found in this species, as previously reported (Maistro et al., 2000; Vicari et al., 2006) and neither additional 5S clusters, as already described by Jesus and Moreira-Filho (2003) and by Vicari et al. (2006) in specimens of P. lineatus from the Mogi Guaçu river and Dourada lagoon, respectively.

The syntenic organization of the 5S and 18S ribosomal genes is a rare event among vertebrates. In addition to P. lineatus (Jesus and Moreira-Filho, 2003; Vicari et al., 2006; Voltolin et al., 2009), this synteny was also observed in Salmo salar (Pendás et al., 1994), Oncorhynchus mykiss (Móran et al., 1996), Astyanax (Almeida-Toledo et al., 2002), in amphibians (Lucchini et al., 1993) and, more recently, in Pimelodus britskii (Moraes-Neto et al., 2011). On the other hand, these loci have been mapped on different chromosomes in many fish species (Martinez et al., 1996; Morán et al., 1996; Born and Bertollo, 2000; Ferro et al., 2001; Vicente et al., 2001; Wasko et al., 2001; Noleto et al., 2007), representing the most frequent condition in vertebrates (Lucchini et al., 1993; Drouin and Muniz De Sá, 1995, Suzuki et al., 1996).

Neither the 5S nor the 18S ribosomal genes have been found in the B microchromosomes of P. lineatus (Jesus and Moreira-Filho, 2003) and of P. nigricans.

C-banding has proven very useful in cytogenetic studies of fish, permitting the identification of constitutive heterochromatin regions. Differences in the amount or distribution of heterochromatin identified by C-banding are considered important for some fish groups and the distribution of C-bands may characterize genera, species and populations (Montovani et al., 2000).

Several C-banding studies have been performed in Prochilodontidae, especially in Prochilodus lineatus. Maistro et al. (2000) reported centromeric and subtelomeric constitutive heterochromatin in the A complement of curimbatás collected in the Mogi-Guaçu river, Pirassununga, São Paulo. However, telomeric C-bands were absent in the chromosome preparations analyzed herein. but the heterochromatic nature of the supernumerary chromosomes was corroborated (Jesus and Moreira-Filho, 2003; Artoni et al., 2006; Voltolin et al., 2009).

Specimens of Prochilodus are characterized by the presence of conspicuous centromeric heterochromatic blocks in the A complement and in all supernumerary chromosomes (Jesus and Moreira-Filho, 2003; Artoni et al., 2006; Voltolin et al., 2009).

In this study, we observed different patterns of heterochromatin distribution in the genomes of some species of Prochilodus.In P. lineatus, constitutive heterochromatin was observed only in the pericentromeric regions of all chromosomes of the standard (A) complement (Figure 4d) and all B chromosomes were heterochromatic. In P. argenteus, P. brevis, P. costatus and P. nigricans, in addition to the centromeric region of all A chromosomes, we also observed a large heterochromatic block on a submetacentric chromosome pair (Figure 4a, b, c, e). In addition to the centromeric C-bands in specimens of P. lineatus from the Mogi Guaçu river, Jesus and Moreira-Filho (2003) also evidenced heterochromatic blocks close to the telomeric region of a submetacentric pair. Despite these small differences in the constitutive heterochromatin distribution in Prochilodus, we can still consider them a cytogenetically conserved group.

Oliveira et al. (2003) confirmed the conservative nature of the chromosome number and morphology in Prochilodontidae and reinforced the idea that small structural chromosome rearrangements may be the main cause of karyotypic diversification in this group. In that study, the authors observed that in Prochilodus mariae from the Orinoco river basin, Venezuela, in addition to the occurrence of constitutive heterochromatin in all centromeres of the autosomes, a heterochromatic block was present in a submetacentric pair, as observed herein in P. argenteus, P. brevis, P. costatus and P. nigricans. Oliveira et al. (2003) also identified differing C-banding patterns between Semaprochilodus kneri and Semaprochilodus laticeps.In S. kneri, constitutive heterochromatin was present in the centromeric regions of all A chromosomes and a conspicuous heterochromatic block occurred on the long arm of pair 24. In S. laticeps, heterochromatin was only found in the pericentromeric regions, as we also observed in P. lineatus.

The presence of heterochromatin only in centromeric regions of the standard A chromosome set, as described herein in P. lineatus, differs from the data published by Maistro et al. (2000) and Jesus and Moreira-Filho (2003) for P. lineatus from the Mogi Guaçu River, the same location of our collections. These authors described the presence of heterochromatin in the centromeric region of all autosomes and in the telomeric regions of some pairs of the A complement.

Nevertheless, the four species analyzed (P. argenteus, P. brevis, P. nigricans and P. costatus) exhibited the same heterochromatin distribution pattern, in full agreement with literature data (Pauls and Bertollo, 1993; Venere et al., 1999; Hatanaka and Galetti Jr, 2004).

Pauls and Bertollo (1983, 1990) stated that the family Prochilodontidae, especially the Prochilodus genus, presented a conserved karyotype, resulting from a conserva-tive chromosome evolution. The data obtained herein are in agreement with this proposed conservatism. The small cytogenetic variations found herein, such as the constitutive heterochromatin distribution and the position of the NOR among the studied Prochilodus, are not sufficient to contradict the strong conservatism proposed for the species of this genus by various authors of numerous cytogenetic studies.

Acknowledgments

The authors are grateful to the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) and Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) for financial support.

Received: November 22, 2012; Accepted: June 9, 2013.

Associate Editor: Yatiyo Yonenaga-Yassuda

License information: This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

• Almeida-Toledo LF, Ozouf-Costaz C, Foresti F, Bonillo C, Porto-Foresti F and Daniel-Silva MFZ (2002) Conservation of the 5S-bearing chromosome pair and co-localization with major rDNA clusters in five species of Astyanax (Pisces, Characidae). Cytogenet Genet Res 97:229-233.
• Artoni RF, Vicari MR, Endler AL, Cavallaro ZI, Jesus CM, Almeida MC, Moreira-Filho O and Bertollo LAC (2006) Banding pattern of A and B chromosome of Prochilodus lineatus (Characiformes, Prochilodontidae), with comments on B chromosome evolution. Genetica 127:277-284.
• Born GG and Bertollo LAC (2000) An XX/XY Sex chromosome system in a fish species, Hoplias malabaricus with a polymorphic NOR bearing X chromosome. Chromosome Res 8:111-118.
• Cavallaro ZI, Bertollo LAC, Perfect F and Camacho JPM (2000) Frequency increase and mitotic stabilization of a B chromosome in fish Prochilodus lineatus Chromosome Res 8:627-634.
• Dias AL, Foresti F and Oliveira C (1998) Synapsis in supernumerary chromosomes of Prochilodus lineatus (Teleostei, Prochilodontidae). Caryologia 51:105-113.
• Drouin G and Muniz De Sá M (1995) The concerted evolution of 5S ribosomal genes linked to the repeat units of other multigene families. Mol Biol Evol 12:481-493.
• Fenochio AS and Bertollo LAC (1988) A simple method for fresh-water fish lymphocyte culture. Braz J Genet 11:847-852.
• Ferro DAM, Moreira-Filho O and Bertollo LAC (2001) Nucleolar organizing regions, 18S and 5S in Astyanax scabripinnis (Pisces, Characidae): Population distribution and functional diversity. Genetica 110:55-62.
• Flecker AS (1996) Ecosystem engineering by a dominant detritivore in a diverse tropical stream. Ecology 77:1845-1854.
• Foresti F, Almeida-Toledo LF and Toledo-Filho SA (1981) Polymorphic nature of nucleolus organizer regions in fishes. Cytogenet Cell Genet 31:137-144.
• Goulding M (1981) Man and Fisheries on an Amazon frontier. Kluwer Academic Publishers, Boston, 137 pp.
• Grass DE, Brassesco MS, Markariani R, Roncati HA, Saka-moto-Hojo ET, Fenocchio AS and Pastori MC (2007) Cytogenetic polymorphism in Prochilodus lineatus (Pisces, Characiformes) from the middle Paraná River, Santa Fe City Argentina. Comp Cytogenet 1:113-119.
• Hatanaka T and Galetti Jr PM (2004) Mapping of the 18S and 5S ribosomal RNA genes in the fish Prochilodus argenteus Agassiz, 1829 (Characiformes, Prochilodontidae). Genetica 122:239-244.
• Howell WM and Black DA (1980) Controlled silver-staining of nucleolus organizer regions with a protective colloidal developer: A 1-step method. Experientia 36:1014-1015.
• Jesus CM and Moreira-Filho O (2003) Chromosomal localization of 5S and 18S rRNA genes in Prochilodus lineatus (Characiformes, Prochilodontidae). Caryologia 56:281-287.
• Levan A, Fredga K and Sandbreg AA (1964) Nomenclature for centromeric position on chromosomes. Hereditas 52:201-220.
• Lowe-McConnell R (1975) Fish Communities in Tropical Freswaters. Longman, New York, 337 pp.
• Lucchini S, Nardi I, Barsacchi G, Batistoni R and Andronico, F (1993) Molecular cytogenetics of the ribosomal (18S + 28S and 5S) DNA loci in primitive and advanced urodele amphibians. Genome 36:762-773.
• Maistro LM, Oliveira C and Foresti F (2000) Cytogenetic analysis of A and B chromosomes of Prochilodus lineatus (Teleostei, Prochilodontidae) using different restriction enzyme banding and staining methods. Genetica 108:119-125.
• Martínez JL, Morán P, Garcia-Vázquez E and Pendás AM (1996) Chromosomal localization of the major and 5S rRNA genes in the European eel (Anguilla anguilla). Cytogenet Cell Genet 73:149-152.
• Martins C and Galetti Jr PM (2001) Two 5S rDNA arrays in Neotropical fish species: Is it a general rule for fishes? Genetica 111:439-446.
• Miller DA, Dev VG, Tantravashi R and Miller OJ (1976) Supression of human nucleolus organizer activity in mouse-human somatic hybrid cells. Exp Cell Res 101:235-243.
• Montovani M, Abel LDS, Mestriner CA and Moreira-Filho O (2000) Accentuated polymorphism of heterochromatin and nucleolar organizer regions in Astyanax scabripinnis (Pisces, Characidae): Tools for understanding karyotype evolution. Genetica 109:161-168.
• Moraes-Neto A, Silva M, Motoso DA, Vicari MR, Almeida MC, Collares-Pereira MJ and Artoni, RF (2011) Karyotype variability in neotropical catfishes of the family Pimelodidae (Teleostei, Siluriforme). Neotrop Ichytiol 9:97-105.
• Morán P, Martinez JL, Garcia-Vásquez E and Pendás AM (1996) Sex chromosome linkage of 5S rDNA in rainbow trout (Oncorhynchus mykiss). Cytogenet Cell Genet 75:145-150.
• Noleto RB, Guimarães FSF, Paludo KS, Vicari MR, Artoni RF and Cestari MM (2007) Genome size evaluation in Tetraodontiform fishes from the Neotropical region. Mar Biotechnol 11:680-685.
• Oliveira C, Saboya SMR, Foresti F, Senhorini JA and Bernardino G (1997) Increased B chromosome frequency and absence of drive in the fish Prochilodus lineatus Heredity 79:473-476.
• Oliveira C, Nirchio M, Granado A and Levy S (2003) Karyotypic characterization of Prochilodus mariae, Semaprochilodus kneri and Semaprochilodus laticeps (Teleostei, Prochilodontidae) from Caicara del Orinoco, Venezuela. Neotrop Ichthyol 1:47-52.
• Pauls E and Bertollo LAC (1983) Evidence for a system of supranumerary chromosomes in Prochilodus scrofa Steindacher 1881 (Pisces, Prochilodontidae). Caryologia 36:307-314.
• Pauls E and Bertollo LAC (1990) Distribution of a supernumerary chromosome system and aspects of karyotypic evolution in the genus Prochilodus (Pisces, Prochilodontidae). Genetica 81:117-123.
• Pendás AM, Morán P, Freije, JP and Garcia-Vásquez E (1994) Chromosomal mapping and nucleotide sequence of two tandem repeats of Atlantic salmon 5S rDNA. Cytogenet Cell Genet 67:31-36.
• Pinkel D, Straume T and Gray JW (1986) Cytogenetic analysis using quantitative, high-sensitivity, fluorescence hybridization. Proc Natl Acad Sci USA 83:2934-2938.
• Sumner AT (1972) Chromosome Banding. Unwin Hyman Inc, Cambridge, 434 pp.
• Suzuki H, Sakurai S and Matsuda Y (1996) Rat DNAr spacer sequence and chromosomal assignment of the genes to the extreme terminal region of chromosome 19. Cytogenet Cell Genet 72:1-4.
• Terencio ML, Schneider CH, Gross MC, Vicari MR and Feldberg E (2012) Stable karyotypes a general rule for the fish of the family Prochilodontidade. Hydrobiologia 686:147-156.
• Vari RP (1983) Phylogenetic relationships of the families Curimatidae, Prochilodontidae, Anostomidae and Chilodontidae (Pisces, Characiformes). Smithson Contrib Zool 378:1-60.
• Venere PC, Miyazawa CS and Galetti Jr PM (1999) New cases of supernumerary chromosomes in characiform fishes. Genet Mol Biol 22:345-349.
• Vicari MR, Almeida MC, Bertollo LAC, Moreira-Filho O and Artoni RF (2006). Cytogenetic analysis and chromosomal characteristics of the polymorphic 18S rDNA in the fish Prochilodus lineatus (Characiformes Prochilodontidae). Genet Mol Biol 29:621-625.
• Vicente VE, Jesus CM and Moreira-Filho O (2001) Chromosomal localization of 5S and 18S rDNA genes in three Parodon species (Pisces, Parodontidae). Caryologia 4:365-369.
• Voltolin TA, Senhorini JA, Oliveira O, Foresti F, Bortolozzi J and Porto-Foresti F (2009) Cytogenetic markers in wild population of curimbatá (Prochilodus lineatus) from Mogi-Guaçu River. Cytologia 74:281-287.
• Wasko AP, Martins C, Wright JM and Galetti Jr PM (2001) Molecular organization of 5S rRNA in fishes of the genus Brycon Genome 44:839-902.
• White TJ, Brunst LS, and Taylor J (1990) Amplification and direct sequencing of fungal ribosomal RNA for phylogenetics. In: Innis MA, Gelfand DH, Sninsky JJ and White TJ (eds) PCR Protocols: A Guide to Methods and Amplications. Academic Press, San Diego, pp 315-322.

Publication Dates

• Publication in this collection
  23 Aug 2013
• Date of issue
  2013

History

• Received
  22 Nov 2012
• Accepted
  09 June 2013