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Genetics and Molecular Biology
Print version ISSN 1415-4757
Genet. Mol. Biol. vol. 21 n. 1 São Paulo Mar. 1998
http://dx.doi.org/10.1590/S1415-47571998000100009
Nuclear DNA content of thirty species of Neotropical fishes
Margarida Lima Carvalho1, Claudio Oliveira 2 and Fausto Foresti 2
1 Departamento de Ciências da Natureza, Universidade Federal do Acre, Rio Branco, Acre, Brasil.
2 Departamento de Morfologia, Instituto de Biociências, UNESP, Campus de Botucatu, 18618-000 Botucatu, São Paulo, Brasil. Send correspondence to C.O.
ABSTRACT
The present paper reports nuclear DNA content in 30 Neotropical freshwater fish species and summarizes the data on other Neotropical species presented in the literature. Among Neotropical fishes, the nuclear DNA content ranges from 1.04 ± 0.09 pg/nucleus in Corydoras cf. simulatus (2n = 62) to 248.0 pg/nucleus in Lepidosiren paradoxa (2n = 38). A general analysis of the data obtained in the present study for each species showed that DNA measurements were practically constant at the individual level, while significant differences were observed among individuals of the same population. This observation was valid for all species analyzed and was more evident in those species that presented other karyotypic particularities such as sex chromosomes or supernumerary chromosomes. The importance of changes in nuclear DNA content in the evolutionary process of Neotropical fishes is discussed.
INTRODUCTION
Fishes are a large group of organisms comprising about 24,618 valid species, which constitute slightly more than one-half of the total number of living vertebrates (Nelson, 1994). Although the total number of living fish species from the Neotropical region is not known, this is probably the richest region of the world, with more than 5,000 species.
Cytogenetic studies of Neotropical fish have greatly expanded over the last few years, and haploid or diploid numbers are currently known for 706 species, including representatives from 207 genera in 38 families of freshwater species (Oliveira et al., 1996) and for about 39 species including representatives from 35 genera in 21 families of saltwater species (Oliveira and Foresti, 1994). In contrast, studies about nuclear DNA content were performed in only about 76 freshwater species and in two saltwater species (Table I).
Table I - DNA content data of Neotropical freshwater fishes.
Species | 2n | Diploid DNA content (picograms) | Reference |
Osteoglossiformes | |||
Arapaimidae | |||
Arapaima gigas | 56* | 1.96 | Hinegardner and Rosen (1972) |
Osteoglossidae | |||
Osteoglossum bicirrhosum | 54 | 2.0 | Hinegardner and Rosen (1972) |
Characiformes | |||
Anostomidae | |||
Nostomus anostomus | 54 | 2.8 | Hinegardner and Rosen (1972) |
Leporinus friderici | 54 | 2.57 ± 0.14 | Present paper |
Leporinus obtusidens | 54 | 2.84 ± 0.25 | Present paper |
Leporinus octofasciatus | 54 | 3.48 ± 0.15 | Present paper |
Leporinus striatus | 54 | 3.4 | Hinegardner and Rosen (1972) |
Leporinus striatus | 54 | 3.12 ± 0.14 | Present paper |
Schizodon intermedius | 54 | 2.85 ± 0.12 | Present paper |
Schizodon nasutus | 54 | 3.11 ± 0.16 | Present paper |
Characidae | |||
Acestrorhynchinae | |||
Oligosarcus paranaensis | 50 | 3.31 ± 0.14 | Present paper |
Chalcidiinae | |||
Chalceus macroleptidotus | 54 | 2.2 | Hinegardner and Rosen (1972) |
Characidiinae | |||
Characidium cf. fasciatus | 50 | 2.37 ± 0.12 | Present paper |
Characinae | |||
Exodon paradoxus | 52* | 3.4 | Hinegardner and Rosen (1972) |
Cheirodontinae | |||
Cheirodon stenodon | 52 | 3.72 ± 0.14 | Present paper |
Cheirodon cf. stenodon | 52 | 3.53 ± 0.11 | Present paper |
Cynopotaminae | |||
Galeocharax knerii | 52 | 3.20 ± 0.11 | Present paper |
Salmininae | |||
Salminus hilarii | 50 | 2.62 ± 0.18 | Present paper |
Serrasalminae | |||
Metynnis hypsauchen | 3.4 | Hinegardner and Rosen (1972) | |
Metynnis roosevelti | 3.4 | Hinegardner and Rosen(1972) | |
Serrasalmus spilopleura | 60 | 2.88 ± 0.10 | Present paper |
Serrasalmus sp. | 62 | 3.2 | Hinegardner and Rosen (1972) |
Tetragonopterinae | |||
Aphyocharax rubropinnis | 50* | 3.4 | Hinegardner and Rosen (1972) |
Astyanax bimaculatus | 50 | 2.09 ± 0.15 | Present paper |
Astyanax fasciatus | 46 | 3.50 ± 0.18 | Present paper |
Astyanax scabripinnis | 50 | 3.74 ± 0.13 | Present paper |
Bryconamericus stramineus | 52 | 3.27 ± 0.13 | Present paper |
Bryconamericus cf. stramineus | 52 | 3.20 ± 0.14 | Present paper |
Bryconamericus cf. stramineus | 52 | 3.26 ± 0.20 | Present paper |
Gymnocorymbus ternetzi | 48 | 4.2 | Hinegardner and Rosen (1972) |
Hemigramus caudovittatus | 50* | 3.4 | Hinegardner and Rosen (1972) |
Hemigramus ocellifer | 48 | 3.4 | Hinegardner and Rosen (1972) |
Moenkhausia oligolepis | 50* | 3.2 | Hinegardner and Rosen (1972) |
Moenkhausia sanctaefilomenae | 50 | 2.75 ± 0.25 | Present paper |
Piabina argentea | 52 | 2.35 ± 0.05 | Present paper |
Chilodontidae | |||
Chilodus punctatus | 54* | 3.2 | Hinegardner and Rosen (1972) |
Curimatidae | |||
Cyphocharax modesta | 54 | 3.20 ± 0.14 | Present paper |
Steindachnerina insculpta | 54 | 2.86 ± 0.22 | Present paper |
Erythrinidae | |||
Hoplias malabaricus | 40 | 2.8 | Hinegardner and Rosen (1972) |
Hoplias malabaricus | 42 | 2.32 ± 0.09 | Present paper |
Gasteropelecidae | |||
Carnegiella strigata | 50-52 | 2.8 | Hinegardner and Rosen (1972) |
Gasteropelecus levis | 2.8 | Hinegardner and Rosen (1972) | |
Lebiasinidae | |||
Pyrrhulina australis | 1.97 ± 0.15 | Present paper | |
Pyrrhulina ranchoviana | 42 | 2.4 | Hinegardner and Rosen (1972) |
Parodontidae | |||
Apareiodon affinis | 54 | 2.53 ± 0.17 | Present paper |
Prochilodontidae | |||
Prochilodus lineatus | 54 | 3.36 ± 0.32 | Present paper |
Siluriformes | |||
Callichthyidae | |||
Aspidoras fuscoguttatus | 44 | 1.51 ± 0.15 | Oliveira et al. (1993b) |
Brochis splendens | 100 | 2.33 ± 0.19 | Oliveira et al. (1993b) |
Callichthys callichthys | 3.4 | Hinegardner and Rosen (1972) | |
Callichthys callichthys | 58 | 1.94 ± 0.15 | Oliveira et al. (1993b) |
Callichthys callichthys | 58 | 1.89 ± 0.24 | Oliveira et al. (1993b) |
Corydoras aeneus | 120 | 8.8 | Hinegardner and Rosen (1972) |
Corydoras aeneus | 60-63 | 2.77 ± 0.22 | Oliveira et al. (1993b) |
Corydoras aeneus | 34 | 6.29 | Turner et al. (1992) |
Corydoras aeneus | 56 | 3.6 | Turner et al. (1992) |
Corydoras arcuatus | 46 | 4.53 ± 0.41 | Oliveira et al. (1992) |
Corydoras barbatus | 64 | 1.73 ± 0.20 | Oliveira et al. (1993a) |
Corydoras barbatus | 64 | 1.87 ± 0.15 | Oliveira et al. (1993a) |
Corydoras elegans | 50 | 6.0 | Hinegardner and Rosen (1972) |
Corydoras flaveolus | 58 | 3.04 ± 0.94 | Oliveira et al. (1992) |
Corydoras julii | 92* | 8.4 | Hinegardner and Rosen (1972) |
Corydoras macropterus | 66 | 1.63 ± 0.10 | Oliveira et al. (1993a) |
Corydoras macropterus | 66 | 1.35 ± 0.22 | Oliveira et al. (1993a) |
Corydoras melanistus | 48 | 6.0 | Hinegardner and Rosen (1972) |
Corydoras metae | 92 | 8.75 ± 1.50 | Oliveira et al. (1992) |
Corydoras myersi | 56* | 4.6 | Hinegardner and Rosen (1972) |
Corydoras nattereri | 40 | 3.57 ± 0.29 | Oliveira et al. (1993a) |
Corydoras prionotos | 68 | 1.19 ± 0.13 | Oliveira et al. (1993a) |
Corydoras prionotos | 86 | 1.64 ± 0.00 | Oliveira et al. (1993a) |
Corydoras punctatus | 44-46 | 5.8 | Hinegardner and Rosen (1972) |
Corydoras reticulatus | 74 | 1.95 ± 0.26 | Oliveira et al. (1992) |
Corydoras schwartzi | 46 | 4.78 ± 0.83 | Oliveira et al. (1992) |
Corydoras simulatus | 62 | 1.29 ± 0.17 | Oliveira et al. (1992) |
Corydoras cf. simulatus | 62 | 1.04 ± 0.09 | Oliveira et al. (1992) |
Corydoras trilineatus | 46 | 4.90 ± 0.65 | Oliveira et al. (1992) |
Corydoras undulatus | 50 | 6.0 | Hinegardner and Rosen (1972) |
Corydoras sp. | 60 | 1.28 ± 0.17 | Oliveira et al. (1992) |
Corydoras sp. | 84 | 2.37 ± 0.34 | Oliveira et al. (1992) |
Dianema urostriata | 62 | 1.18 ± 0.07 | Oliveira et al. (1993b) |
Hoplosternum sp. | 60 | 1.36 ± 0.11 | Oliveira et al. (1993b) |
Doradidae | |||
Acanthodoras spinosissimus | 3.2 | Hinegardner and Rosen (1972) | |
Loricariidae | |||
Hypoptopomatinae | |||
Microlepidogaster sp. | 1.78 ± 0.10 | Present paper | |
Otocinclus affinis | 54* | 4.2 | Hinegardner and Rosen (1972) |
Hypostominae | |||
Hypostomus cf. ancistroides | 3.17 ± 0.17 | Present paper | |
Hypostomus plecostomus | 54 | 4.2 | Hinegardner and Rosen (1972) |
Loricariinae | |||
Loricaria parva | 48 | 3.2 | Hinegardner and Rosen (1972) |
Xenocara dolichoptera | 3.6 | Hinegardner and Rosen (1972) | |
Pimelodidae | |||
Pimelodinae | |||
Imparfinis mirini | 2.06 ± 0.14 | Present paper | |
Pimelodella gracilis | 46* | 1.76 | Hinegardner and Rosen (1972) |
Pimelodus clarias | 56* | 2.4 | Hinegardner and Rosen (1972) |
Pimelodus maculatus | 2.68 ± 0.22 | Present paper | |
Gymnotiformes | |||
Apteronotidae | |||
Apteronotus albifrons | 22 | 1.42 | Hinegardner and Rosen (1972) |
Gymnotidae | |||
Gymnotus carapo | 38 | 1.98 | Hinegardner and Rosen (1972) |
Sternopygidae | |||
Eigenmannia sp. | 34 | 2.0 | Hinegardner and Rosen (1972) |
Sternpygus macrurus | 48 | 1.98 | Hinegardner and Rosen (1972) |
Cyprinodontiformes | |||
Cyprinodontidae | |||
Poecilia latipinna | 48 | 1.92 | Hinegardner and Rosen (1972) |
Poecilia m. mexicana | 46 | 1.5-1.6 | Sola et al. (1992) |
Poecilia m. mexicana | 3n = 69 | 2.1-2.2 | Sola et al. (1992) |
Xiphophorus alvarezi** | 1.52 | Tiersch et al. (1989a) | |
Xiphophorus andersi** | 1.485 | Tiersch et al. (1989a) | |
Xiphophorus cortezi** | 1.535 | Tiersch et al. (1989a) | |
Xiphophorus couchianus** | 1.50 | Tiersch et al. (1989a) | |
Xiphophorus helleri | 48 | 1.9 | Hinegardner and Rosen (1972) |
Xiphophorus helleri** | 48* | 1.545 | Tiersch et al. (1989a) |
Xiphophorus maculatus | 48 | 1.9 | Hinegardner and Rosen (1972) |
Xiphophorus maculatus** | 48* | 1.51 | Tiersch et al. (1989a) |
Xiphophorus meyersi** | 1.495 | Tiersch et al. (1989a) | |
Xiphophorus montezumae | 48* | 1.52 ± 0.01 | Tiersch et al. (1989a) |
Xiphophorus pygmaeus** | 1.487 | Tiersch et al. (1989a) | |
Rivulidae | |||
Rivulus urophthalmus | 44 | 3.0 | Hinegardner and Rosen (1972) |
Perciformes | |||
Cichlidae | |||
Aequidens portalegrensis | 48* | 2.4 | Hinegardner and Rosen (1972) |
Apistograma sp. | 2.0 | Hinegardner and Rosen (1972) | |
Cichlasoma biocellatum | 2.6 | Hinegardner and Rosen (1972) | |
Cichlasoma meeki | 48 | 2.8 | Hinegardner and Rosen (1972) |
Crenicichla saxatilis | 48* | 2.2 | Hinegardner and Rosen (1972) |
Geophagus jurupari | 48* | 2.4 | Hinegardner and Rosen (1972) |
Pterophyllum eimekei | 48 | 2.4 | Hinegardner and Rosen (1972) |
Scianidae | |||
Menticirrhus americanus | 48 | 1.57 ± 0.03 | Gomes et al. (1983b) |
Micropogonias furnieri | 48 | 1.24 ± 0.01 | Gomes et al. (1983a) |
Lepidosireniformes | |||
Lepidosirenidae | |||
Lepidosiren paradoxa | 38 | 248.0 | Ohno and Atkin (1966) |
*Diploid numbers cited by Oliveira et al. (1988).
**Mean values obtained by the authors for different lines.
Several evolutionary studies of Neotropical fishes have suggested the occurrence of drastic chromosomal rearrangements (e.g. Feldberg et al., 1993) and sometimes polyploidy (e.g. Oliveira et al., 1993b); thus, the determination of nuclear DNA content would be very important to better understand the overall evolutionary process in Neotropical fishes. Moreover, the wide variability of nuclear DNA content found among fishes led Ohno (1974) to state that comparative karyotype studies in this group would be very limited without information about genome size variation. The main objective of this paper was to employ a cytological technique to estimate the nuclear DNA content in fish erythrocytes from 30 Neotropical species and compare it with fishes previously studied, in order to provide new information for the study of evolutionary steps in this group of vertebrates.
MATERIAL AND METHODS
Thirty species of fishes were used in the present study. Their taxonomic status, collection site, and the number and sex of specimens analyzed are presented in Table II. After processing, all specimens were fixed and maintained in the fish collection of the Laboratory of Genetics and Fish Biology, Instituto de Biociências, Universidade Estadual Paulista, Botucatu, São Paulo, Brazil.
Table II - Species analyzed.
Species | Collection site | Number of fish analyzed males/females/not sexed |
Leporinus friderici | Represa de Jurumirim, Itatinga, SP | 1/4/0 |
Leporinus obtusidens | Represa de Jurumirim, Itatinga, SP | 3/6/1 |
Leporinus obtusidens | Pisciculture - CEMIG, MG | 0/0/10 |
Leporinus octofasciatus | Represa de Jurumirim, Itatinga, SP | 2/0/0 |
Leporinus striatus | Represa de Jurumirim, Itatinga, SP | 1/3/0 |
Schizodon intermedius | Represa de Jurumirim, Itatinga, SP | 2/2/0 |
Schizodon nasutus | Represa de Jurumirim, Itatinga, SP | 1/6/0 |
Oligosarcus paranaensis | Córrego da Jacutinga, Bofete, SP | 6/4/0 |
Characidium cf. fasciatus | Represa de Jurumirim, Itatinga, SP | 7/2/0 |
Cheirodon stenodon | Represa de Jurumirim, Itatinga, SP | 3/9/0 |
Cheirodon cf. stenodon | Represa de Jurumirim, Itatinga, SP | 2/8/0 |
Galeocharax knerii | Represa de Jurumirim, Itatinga, SP | 3/7/0 |
Salminus hilarii | Represa de Jurumirim, Itatinga, SP | 7/2/1 |
Serrasalmus spilopleura | Represa de Jurumirim, Itatinga, SP | 7/6/0 |
Astyanax bimaculatus | Represa de Jurumirim, Itatinga, SP | 4/6/0 |
Astyanax fasciatus | Represa de Jurumirim, Itatinga, SP | 2/8/0 |
Astyanax scabripinnis | Rio Capivara, Botucatu, SP | 7/3/0 |
Bryconamericus stramineus | Represa de Jurumirim, Itatinga, SP | 5/5/0 |
Bryconamericus cf. stramineus | Ribeirão da Quinta, Itatinga, SP | 3/2/5 |
Bryconamericus cf. stramineus | Córrego Hortelã, Botucatu, SP | 3/7/0 |
Moenkhausia sanctaefimolenae | Rio Capivara, Botucatu, SP | 6/3/1 |
Piabina argentea | Represa de Jurumirim, Itatinga, SP | 6/4/0 |
Cyphocharax modesta | Represa de Jurumirim, Itatinga, SP | 3/5/0 |
Steindachnerina insculpta | Represa de Jurumirim, Itatinga, SP | 5/5/0 |
Hoplias malabaricus | Represa de Jurumirim, Itatinga, SP | 1/0/2 |
Pyrrhulina australis | Córrego da Barra Funda, São José do Rio Preto, SP | 5/5/0 |
Apareiodon affinis | Represa de Jurumirim, Itatinga, SP | 2/2/1 |
Prochilodus lineatus | Represa de Jurumirim, Itatinga, SP | 5/3/0 |
Hypostomus cf. ancistroides | Córrego da Jacutinga, Bofete, SP | 7/1/0 |
Microlepidogaster sp. | Córrego da Jacutinga, Bofete, SP | 5/5/0 |
Imparfinis mirini | Córrego da Jacutinga, Bofete, SP | 3/5/0 |
Pimelodus maculatus | Represa de Jurumirim, Itatinga, SP | 2/4/4 |
Mitotic chromosome preparations were obtained from kidney and gill cells using the air-drying technique described by Foresti et al. (1993). Relative DNA content of each fish was determined according to the technique described by Gold and Price (1985) with some minor modifications. Blood was collected by caudal puncture and smeared near the frosted end of three slides. Blood smears from chicken, common carp, and rainbow trout served as standard references for DNA quantification. Absorbance values of fish nuclei from each slide were standardized as a percentage of the mean absorbance value of the three controls: chicken erythrocytes, common carp erythrocytes, and rainbow trout erythrocytes. For conversion to picograms (pg) of DNA, the standardized data were multiplied by known values for these species (2.5 pg, 3.4 pg, and 5.5 pg, respectively, according to Tiersch et al., 1989b). Chicken blood was obtained from a Hamphisare strain male; rainbow trout and common carp blood was obtained from domestic stocks. The slides were fixed for 20 min in 9:1 methanol-formaldehyde (37%), rinsed twice (10 min each) in distilled water, dehydrated in 70% ethanol (2 min) and 95% ethanol (2 min), and stored overnight under desiccative conditions at 4°C. The following day, individual batches of 20 randomized slides were hydrolyzed for 15 min in 1.0 N HCl at 60°C, rinsed briefly in distilled water, and stained for 2 h in Schiffs reagent (Feulgen stain). Hydrolysis time was determined empirically as the point of maximum absorbance in a hydrolysis curve. Following staining, the slides were rinsed twice (10 min each) in SO2 water and once (10 min) in distilled water, air dried in the dark and analyzed.
Microdensitometry analysis was performed under a Zeiss microscope using a 100X oil-immersion objective. Analyses were done using OPTIMAS software version 4.1. For each fish, 15 nuclei were measured from two slides each (30 nuclei per individual). The third slide prepared from each specimen served as a backup in case of breakage. Only nuclei which were roughly spherical, homogeneously Feulgen-stained and from clear slide areas were chosen for measurement. The decision to measure 30 nuclei per individual was based on preliminary experiments (measurements of 10-300 cells per slide and over 20 slides) that showed an average coefficient of variation (per slide and per individual) of 1-3%. This means that measuring 30 nuclei per fish should distinguish a 1-3% difference in mean genome size at a- and b-probability levels of 0.05 (Gold et al., 1975).
RESULTS AND DISCUSSION
Including the present data, nuclear DNA content is known for 106 freshwater fish species from the Neotropical region and ranges from 1.04 ± 0.09 pg/nucleus in Corydoras cf. simulatus (2n = 62) to 248.0 pg/nucleus in Lepidosiren paradoxa (2n = 38) (Table I). However, a general analysis of Table I shows that only the families Callichthyidae (26 species) and Cyprinodontidae (11 species) were relatively well studied, while for all other groups only a few isolated data are known.
A general analysis of the data obtained in the present study for each species showed that at the individual level the coefficient of variation for DNA content was about 1%, while the coefficient of variation at the species level was about 4-6%. These data showed that while for each specimen the nuclear DNA content is practically constant, at the species or local population level there is a wider range of variation. This observation was valid for all species analyzed and was more evident in those species which presented other karyotypic particularities such as sex chromosomes or supernumerary chromosomes. Furthermore, it agrees with other studies, which also observed large differences in genome size among local populations and significant differences among specimens of the same population (Gold and Price, 1985; Gold and Amemiya, 1987; Johnson et al., 1987; Ragland and Gold, 1989; Tiersch et al., 1989a; Oliveira et al., 1992).
DNA content analysis of Characidium cf. fasciatus, which has a ZZ/ZW sex chromosome system (Maistro et al., 1996), showed that six males had less DNA than two females. On the other hand, one male presented more DNA than the females. In this species the W chromosome is larger than the Z chromosome. Considering that a variable number of medium-sized supernumerary chromosomes was found in the cells of the individuals analyzed, we suggest that they could be responsible for the additional DNA content in the cells of this male.
The presence of supernumerary chromosomes produced a large coefficient of variation in the values obtained for Moenkhausia sanctaefilomenae (9.15%), Steindachnerina insculpta (7.71%), and Prochilodus lineatus (9.42%). Since these species presented a variable number of supernumerary microchromosomes among different specimens of each population, the occurrence of such genomic elements could cause individual differences in DNA content in the populations. In the future we intend to analyze specifically the relationship between the number of supernumerary chromosomes and DNA content variation. The objective would be to estimate the size and real participation of these additional chromosomes in the genomic configuration of each individual.
As a general remark, it was observed that the variation of DNA content inside each family or sub-family analyzed was equal or similar to that observed for its respective order. Thus, among Anostomidae the nuclear DNA content ranged from 2.57 ± 0.14 pg for Leporinus friderici to 3.48 ± 0.15 pg for Leporinus octofasciatus (Table I). Considering that both species have 2n = 54 chromosomes and similar karyotypes with only metacentric and submetacentric chromosomes (Galetti Jr. et al., 1981), the difference in nuclear DNA content may be distributed among the chromosomes. Among the Tetragonopterinae, the nuclear DNA content ranged from 2.09 ± 0.15 for Astyanax bimaculatus to 3.74 ± 0.13 for A. scabripinnis (Table I). In this case, both species have 2n = 50 chromosomes; however, C- banding showed that A. scabripinnis presents large heterochromatic segments which are not observed in A. bimaculatus (Daniel-Silva, 1996). The occurrence of differences in nuclear DNA content among species of the same group was observed previously in different situations (Thode et al., 1985; Majumdar and McAndrew, 1986; Oliveira et al., 1992, 1993a; among others).
In a study of nuclear DNA content of 275 teleost species, Hinegardner and Rosen (1972) found that the modal value observed was 2.0 pg. Analysis of data available for the order Characiformes showed that species of this group present a mean value of 3.0 pg, which represents 1.0 pg above the mean value observed for fishes by Hinegardner and Rosen (1972). Analysis of the data available for the order Siluriformes showed that species of this group present a mean value of 3.4 pg, which represents 1.4 pg above the mean value observed for fishes by Hinegardner and Rosen (1972).
The more specialized or evolutionarily advanced fishes usually have less DNA than the more generalized forms; however, there are several exceptions, which may represent fish groups that are now in the process of evolutionary radiation (Hinegardner and Rosen, 1972). Although several exceptions to this rule are known, the data obtained for the orders Siluriformes and Characiformes are in accordance with it since their superorder Ostariophysi is a primitive group of fishes (Nelson, 1994).
Although the data obtained in the present investigation have significantly increased the number of species whose nuclear DNA content is known, these data are still insufficient when compared to the known number of fish species in the Neotropical region. Considering the wide variation of nuclear DNA content in the species already studied, future studies are necessary to better evaluate the relationship between changes in DNA content and the evolutionary process in Neotropical fishes.
ACKNOWLEDGMENTS
The authors are grateful to Dr. F. Langeani Filho for taxonomic identification of the specimens, R. Devidé, R.T.C. Dellevedove, M.R. Vieira, and P.C. Vissotto for technical assistance, and Dr. V. Dal Pai for the use of the micro-densitometer. The chicken blood used was provided by Mr. Heraldo Emílio from the Biotério Central of UNESP, Botucatu, SP, Brazil; common carp blood was provided by Mr. João Batista from CAUNESP, Jaboticabal, SP, and rainbow trout blood was provided by MsC. Marcos Guilherme Rigolino from Estação Experimental de Salmonicultura, Campos do Jordão, SP. Research supported by FAPESP, CAPES, CNPq, and FUNDUNESP. Publication supported by FAPESP.
RESUMO
O presente trabalho descreve os dados obtidos da análise de conteúdo de DNA nuclear de 30 espécies de peixes Neotropicais de água doce e apresenta uma revisão dos dados disponíveis sobre o conteúdo de DNA nuclear para as espécies Neotropicais. Entre os peixes Neotropicais, o conteúdo nuclear de DNA varia de 1,04 ± 0,09 pg/núcleo em Corydoras cf. simulatus (2n = 62) a 248,0 pg/núcleo em Lepidosiren paradoxa (2n = 38). Uma análise geral dos dados obtidos no presente estudo para cada espécie mostrou que a nível de indivíduo as medidas de DNA foram praticamente constantes, enquanto diferenças significativas foram observadas entre indivíduos da mesma população. Essa observação foi válida para todas as espécies analisadas e foi mais evidente naquelas espécies que apresentaram outras particularidades cariotípicas como a presença de cromossomos sexuais ou supranumerários. A importância das alterações no conteúdo de DNA nuclear no processo evolutivo dos peixes Neotropicais é discutida.
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(Received March 6, 1997)