Karyotypic diversity among three species of the genus Astyanax (Characiformes: Characidae)

Diversidade Cariotípica entre três espécies do gênero Astyanax (Characiformes, Characidae)

P. B. Nishiyama M. M. R. Vieira F. E. Porto L. A. Borin A. L. B. Portela-Castro I. C. M. Santos About the authors

Abstract

The group Incertae sedis within the Characidae family currently includes 88 genera, previously included in the subfamily Tetragonopterinae. Among them is the genus Astyanax comprising a group of species with similar morphology and widely distributed in the Neotropics. Thus, the present study aimed to analyze the karyotype diversity in Astyanax species from different watersheds by conventional Giemsa staining, C-banding and fluorescence in situ hybridization (FISH rDNA 18S) probe.specimens of Astyanax aff. paranae belonging to the “scabripinnis complex”, Astyanax asunsionensis and Astyanax aff. bimaculatus were analyzed”. Two sympatric karyomorphs were observed in Astyanax.aff paranae, one of them having2n=48andthe other one with 2n=50 chromosomes. Other population of this same species also presented 2n=50 chromosomes, but differing in the karyotype formula and with macro supernumerary chromosome found in 100% of the cells in about 80%of females analyzed. Two population of A. asuncionensis and one population of Astyanax. aff. bimaculatus, also showed a diploid number of 50 chromosomes, but also differing in their karyotype formulas. Therefore, A. asuncionensis was also characterized by intraspecific chromosome diversity. The C-banding analysis was able to demonstrate a distinctable to demonstrate a distinct pattern of heterochromatin differing A. asuncionensis from Astyanax aff. paranae and Astyanax aff. bimaculatus. The supernumerary chromosome of Astyanax aff. paranae proved completely heterochromatic. Only Astyanax.aff. bimaculatus multiple showed multiple sites of nucleolar organizing regions. The other species were characterized by having a simple system of NOR. These data contributes to the know ledge of the existing biodiversity in our fish fauna, here highlighted by the inter- and intraspecific chromosomal diversity in the genus Astyanax.

Keywords:
cytogenetics; biodiversity; B chromosomes; C-bands; NORs

Resumo

O grupo Incertae sedis, dentro da família Characidae inclui atualmente 88 gêneros, anteriormente incluídos na subfamília Tetragonopterinae. Dentre eles encontra-se o gênero Astyanax que compreende um grupo de espécies com morfologia similar e com ampla distribuição na região Neotropical. Assim, o presente estudo teve como objetivo analisar a diversidade cariotípica em espécies de Astyanax de diferentes bacias hidrográficas, através da coloração convencional com Giemsa, bandeamento C e hibridização fluorescente in situ (FISH com rDNA 18S). Exemplares de Astyanax aff. paranae, pertencentes ao “complexo scabripinnis”; Astyanax asunsionensise Astyanax aff. bimaculatus foram analisados. Dois cariomorfos foram observados em A. aff. paranae, um deles com 2n=48 cromossomos e outro com 2n=50 cromossomos. Outra população apresentou 2n=50 cromossomos, ambas diferindo na fórmula cariotípica e um cromossomo supranumerário encontrado em 100% das células, em aproximadamente 80% das fêmeas analisadas. Populações de A.asunsionensis e uma população de Astyanax aff. Bimaculatus também mostraram número diplóide de 50 cromossomos, mas diferindo em suas fórmulas cariotípicas. Portanto, A. asuncionensis foi também caracterizado por uma diversidade cariotípica intraespecífica. As análises de bandeamento C foi capaz de demonstrar um padrão distinto de heterocromatina, diferindo A. asuncionensis de A.aff. paranae e A. aff. bimaculatus. O cromossomo supranumerário de Astyanax aff. paranae mostrou-se completamente heterocromático. Apenas Astyanax aff. bimaculatus mostrou múltiplos sítios de regiões organizadoras de nucléolo(NORs). As outras espécies foram caraterizadas por apresentar um sistema simples de NOR. Estes dados contribuem para o conhecimento da existência de biodiversidade em nossa fauna de peixes, aqui em destaque pela diversidade cromossômica inter e intraespecífica no gênero Astyanax.

Palavras-chave:
citogenética; biodiversidade; cromossomos B; bandas C; NORs

1 Introduction

Teleost fishes, which make up about half of the species of vertebrates have an incredible level of biodiversity (Volff, 2005Volff, J.N., 2005. Genome evolution and biodiversity in teleost fish. Heredity, vol. 94, no. 3, pp. 280-294. http://dx.doi.org/10.1038/sj.hdy.6800635. PMid:15674378.
http://dx.doi.org/10.1038/sj.hdy.6800635...
). According to Nelson (2006)Nelson, J.S., 2006. Fishes of the world. 4th ed. New York: Wiley., they constitute a very favorable group for evolutionary studies, in view of their basal position in the phylogeny of vertebrates, with a large number of species dispersed in the Neotropical region.Characidae is one of the most complex families within Characiformes fishes,presenting a diverse range of forms, which allowed them to occupy many different habitats, with diversification of food processes and reproductive strategies (Graça and Pavanelli, 2007Graça, W.J. and Pavanelli, C.S., 2007. Peixes da planície de inundação do Alto Rio Paraná e áreas adjacentes. Maringá: Eduem. 241 p.).However, for Lucena (1993)Lucena, C.A.S., 1993. Estudo filogenético da família Characidae com uma discussão dos grupos naturais propostos (Teleostei, Ostariophysi, Characiformes). São Paulo: Instituto de Biociências, Universidade de São Paulo. Tese de Doutorado em Ciências Biológicas., these characteristics have hampered the classification of its copies and the of kinship relations with other Characiformes families.

Given the complexity of characins, 620 species are included within an Incertae Sedis group, including Astyanax representatives (Lima et al., 2003Lima, F.C.T., Malabarba, L.R., Buckup, P.A., Silva, J.F.P., Vari, R.P., Harold, A., Benine, R., Oyakawa, O.T., Pavanelli, C.S. and Menezes, N.A., 2003. Genera Incertae Sedis in Characidae. In: R.E. REIS; S.O. KULLANDER; J.R. FERRARIS, eds. Check list of the freshwater fishes of South and Central America. Porto Alegre: Edipucrs, pp. 106-169.). Studies by Mirande (2010)MIRANDE, J.M., 2010. Phylogeny of the family Characidae (Teleostei: Characiformes): from characters to taxonomy. Neotropical Ichthyology, vol. 8, no. 3, pp. 385-568. the principal objective of the proposed taxonomic nomenclature is to classify members of the Characidae in monophyletic units, this works includes the genus Astyanax asunsionensis in Clade Astyanax. Cytogenetic studies performed by Moreira-Filho and Bertollo (1991)Moreira-Filho, O. and Bertollo, L.A.C., 1991. (Pisces;Characidae): a “species complex”. Astyanax scabripinnisRevista Brasileira de Genetica, vol. 14, pp. 331-357., particularly in A. scabripinnis revealed a group of species that were named “scabripinnis complex”. Graça and Pavanelli, (2007)Graça, W.J. and Pavanelli, C.S., 2007. Peixes da planície de inundação do Alto Rio Paraná e áreas adjacentes. Maringá: Eduem. 241 p., considered Astyanax. aff. paranae as part of this complex.

Astyanax have presented an extensive diversity in the chromosome number and karyotype formula, both intra- and interspecifically, besides the occurrence of B chromosomes and natural polyploidy for some populations (Malacrida et al., 2003Malacrida, A.C.C.P., Dias, A.L. and Giuliano-Caetano, L., 2003. Natural triploidy in Astyanax aff. scabripinnis (Pisces,Characidae) of the Tibagi river bay-PR. Cytologia, vol. 68, no. 3, pp. 267-270. http://dx.doi.org/10.1508/cytologia.68.267.
http://dx.doi.org/10.1508/cytologia.68.2...
; Gross et al., 2004Gross, M.C., Schneider, C.H., Matiello, M.C.A., Leite, M.L., Bertollo, L.A.C. and Artoni, R.F., 2004. Population structure, fluctuating asymmetry and genetic variability in an endemic and highly isolated . Astyanax fish population (Characidae)Genetics and Molecular Biology, vol. 27, no. 4, pp. 529-535. http://dx.doi.org/10.1590/S1415-47572004000400011.
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; Kantek et al., 2007Kantek, D.L.Z., Noleto, R.B., Fenocchio, A.S. and Cestari, M.M., 2007. Cytotaxonomy, heterochromatic polymorphism and natural triploidy of a species of . Astyanax (Pisces, Characidae) endemic to the Iguaçu River basinBrazilian Archives of Biology and Technology, vol. 50, no. 1, pp. 67-74. http://dx.doi.org/10.1590/S1516-89132007000100008.
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; Peres et al., 2009Peres, W.A.M., Buckup, P.A., Kantek, D.L.Z., Bertollo, L.A.C. and Moreira-Filho, O., 2009. Chromosomal evidence of downstream dispersal of Astyanax fasciatus (Characiformes, Characidae) associated with river shed interconnection. Genetica, vol. 137, no. 3, pp. 305-311. http://dx.doi.org/10.1007/s10709-009-9389-4. PMid:19641999.
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; Santos et al., 2012Santos, N.M., Ferreira-Neto, M., Artoni, R.F., Vicari, M.R., Bakkali, M., Oliveira, C. and Foresti, F., 2012. A comparative structural cytogenetic study in three allopatric populations of (Teleostei: Characidae). Astyanax scabripinnisZoologia, vol. 29, no. 2, pp. 159-166.).

The present study aimed to analyse different populations of three Astyanax species using conventional and molecular cytogenetic procedures, order to contribute to the knowledge biodiversity in this fish group.

2 Material and Methods

Seventy-one specimens belonging to three species of the genus Astyanax were colleted. Two populations of Astyanax aff. paranae from Paraná River basin, Maringá/PR region: Andirá stream – 23°22’02”S, 52°11’42”W (4 males and 2 females) and Itiz stream – 23°32’11.2”S, 51°46’59”W (5 males and 8 females). One population of Astyanax aff. bimaculatus from Pardo River Basin,Vitória da Conquista/BA region: Bateias lagoon – 14°51’26”S, 40°52’13”W (8 males and 12 females). Two populations of A.asuncionensis from upper Paraguay River basin Coxim/MS region: Onça stream- 18°30’S, 54°39’W (9 males and 6 females) and Criminoso stream – 18°29'21”S, 54°45'13,9”W (10 males and 7 females). The specimens were deposited in the collection of Laboratory of the Zoology Universidade Federal da Bahia, Vitória da Conquista/BA.

Mitotic chromosomes were performed according to the technique “air drying” as modified for fish by Bertollo et al. (1978)Bertollo, L.A.C., Takahashi, C.S. and Moreira-Filho, O., 1978. Cytotaxonomic considerations on (Pisces, Erythrinidae). Hoplias lacerdaeBrazilian Journal of Genetics, vol. 1, pp. 103-120.. The prepared slides were stained with Giemsa for conventional studies, to determine the number and morphology of chromosomes. The constitutive heterochromatin (C-banding) was performed according to Sumner (1972)SumNer, A.T., 1972. A simple techique for demonstrating centromeric heterocromation. Exptl. Cell Res. Research, vol. 75, no. 1, pp. 304-306. http://dx.doi.org/10.1016/0014-4827(72)90558-7.
http://dx.doi.org/10.1016/0014-4827(72)9...
, with some minor adjustments (Lui et al., 2009Lui, R.L., Blanco, D.R., Margarido, V.P. and Moreira-Filho, O., 2009. First description of B chromosomes in the family Auchenipteridae, . Parauchenipterus galeatus (Siluriformes) of the São Francisco River basin (MG, Brazil)Micron (Oxford, England), vol. 40, no. 5-6, pp. 552-559. http://dx.doi.org/10.1016/j.micron.2009.03.004. PMid:19394233.
http://dx.doi.org/10.1016/j.micron.2009....
). The nucleolar organizing regions (NORs sites) were identified by fluorescence in situ hybridization (FISH), with rDNA 18S probe, according to Pinkel et al. (1986)Pinkel, D., Straume, T. and Gray, J.W., 1986. Cytogenetic analysis using quantitative, high-sensitivity, fluorescence hybridization. Proceedings of the National Academy of Sciences of the United States of America, vol. 83, no. 9, pp. 2934-2938. http://dx.doi.org/10.1073/pnas.83.9.2934. PMid:3458254.
http://dx.doi.org/10.1073/pnas.83.9.2934...
.The chromosomes were classified as metacentric (m), submetacentric (sm) subtelocentric (st) and acrocentric (a) according to Levan et al. (1964)Levan, A., Fredga, K. and Sandberg, A.A., 1964. Nomenclature for centromeric position on chromosomes. Hereditas, vol. 52, no. 2, pp. 201-220. http://dx.doi.org/10.1111/j.1601-5223.1964.tb01953.x.
http://dx.doi.org/10.1111/j.1601-5223.19...
.

3 Results

3.1 Astyanax aff. paranae

Two populations of this species were analyzed in this study, one Andirá stream (A population) and another from Itiz stream (B Population). However, two distinct karyotypes were identified in the A population, one with 2n=48 chromosomes,14m + 18sm + 6st e 10a (Figure 1a); and the other with 2n=50 chromosomes,8m + 22sm + 6st + 14a (Figure 1b). B Population showed 2n=50 chromosomes, with 12m + 16sm + 6st + 16a, and with also a macro supernumerary chromosome, similar in size to the first pair of metacentric chromosome found in 100% of the cells of about 80% of the females analized (Figure 1c).

Figure 1
Karyotype of the Astyanax aff. paranae, Andirá stream: (a) specimens with 2n=48 chromosomes and (b) specimens with 2n=50 chormosomes; (c) Astyanax aff. paranae, Itiz stream: 2n=50 chromosomes plus a macro supernumerary metacentric chromosome; (d) Astyanax aff. bimaculatus from Bateias Lagoon: 2n=50chromosomes; (e) Astyanax asuncionensis, Criminoso stream: 2n=50 chromosomes and (f) Astyanax asuncionensis, from Onça stream: 2n=50 chromosomes.

All specimens of Astyanax aff.paranae showed a discrete localization of heterochromatin in the centromeric region of the chromosomes, plus some pairs with conspicuous telomeric blocks. The supernumerary chromosome of the population from Itiz stream was completely heterochromatic (Figure 2a-c).

Figure 2
C-banded metaphases of (a) Astyanax aff. paranae (2n=48) from Andirá stream, (b) Astyanax aff. paranae (2n=50) from Andirá stream, (c) Astyanax aff. paranae from Itiz stream, (d) Astyanax aff. bimaculatus from Bateias Lagoon, (e) Astyanax assuncionensis from Criminoso stream, (f) Astyanax asuncionensis from Onça stream.

NORs were present in the short arm of only one submetacentric pair, with eventual size polymorphism between the homologous (Figure 3a-c).

Figure 3
FISH with rDNA 18S probe in Astyanax aff. paranae, Andirá stream (2n=48); Astyanax aff. paranae from Andirá stream (2n=50); Astyanax aff. paranae from Itiz stream; Astyanax aff. bimaculatus from Bateias Lagoon; Astyanax asuncionensis from Criminoso stream; Astyanax asuncionensis from Onça stream. Chromosome pairs bearing NOR by arrows.

3.2 Astyanaxaff.bimaculatus

Astyanax aff. bimaculatus from Bateias Lagoon showed 2n=50 chromosomes,with10m + 24sm + 8st + 8a (Figure 1d). C-bands were also discrete and with a preferential pericentromeric distribution, although with interstitial markings in some chromosomes of the complement (Figure 2d). A system of multiple-NOR, comprising two pairs of submetacentric chromosomes was identified for this species (Figure 3c).

3.3 Astyanaxasuncionensis

The two populations of A.asuncionensis, from Criminoso stream (A population) and Onça stream (B population) showed 2n=50 chromosomes, but with variations in karyotype formulas. Population Ahighlighted8m + 30sm + 6st + 6a (Figure 1e) and population B showed 6m + 24SM + 10st + 10a (Figure 1f). The general distribution pattern of the constitutive heterochromatin was similar in the two populations with pericentromeric and/or interstitial blocks in some chromosomes pairs, besides conspicuous terminal blocks coinciding with NORs (Figure 2e, f). In both populations only a pair of submetacentric pair evidenced telomeric NORs on the short arms (Figure 3e, f).

4 Discussion

Astyanax aff.paranae, considered as part of the “scabripinnis complex” (Graça and Pavanelli, 2007Graça, W.J. and Pavanelli, C.S., 2007. Peixes da planície de inundação do Alto Rio Paraná e áreas adjacentes. Maringá: Eduem. 241 p.), highlighted two sympatric karyomorphs in the Andirá stream (populations A and B) showing distinct diploid numbers and karyotypic formulas. In addition, specimens from Itiz stream, although showing a relative similarity with karyomorph B, display a macro supernumerary chromosome characteristic for this population. Modifications in the diploid numbers and in the karyotypic formulas indicate that distinct rearrangements took place in the chromosome evolution of these fishes, such as Robertsonian rearrangements and that ones modifying the centromere position. It is outstanding that the subtelocentric chromosomes were the most conservative ones, keeping the same number in most species now analyzed. Fernandes and Martins-Santos (2005)Fernandes, C.A. and Martins-Santos, I.C., 2005. Sympatric occurence of three cytotypes and four morphological types of B chromosomes in Astyanax scabripinnis (Pisces, Characiformes) in the river Ivaí basin, state Paraná, Brasil. Genetica, vol. 124, pp. 301-306. analyzing A. scabripinnis from Tatupeba stream, also highlight the role of Robertsonian rearrangements, such as centric fusions, in the karyotype differentiation of this species, where specimens with 2n=46, 48 and 50 chromosomes were found in sympatry indicating that in this locality three distinct species. appear to coexist. Similarly the two karyomorphs from Andirá stream indicate the coexistence of two probable cryptic species which, together with the population of Itiz stream and compared with studies Vicari et al. (2008)VICARI, M.R., NOLETO, R.B., ARTONI, R.F., MOREIRA-FILHO, O. and BERTOLLO, L.A.C., 2008. Comparative cytogenetics among species of the Astyanax scabripinnis complex. Evolutionary and biogeographical inferences. Genetics and Molecular Biology, vol. 31, no. 1, pp. 173-179., supporta likely species complex in Astyanax aff. paranae. According to these authors, the number of the species in this complex is subestimated. As a whole, the available data indicate that the karyotype evolution in this fish group is very dynamic and goes beyond the 'simple' accumulation of chromosomal rearrangements (Santos et al., 2012Santos, N.M., Ferreira-Neto, M., Artoni, R.F., Vicari, M.R., Bakkali, M., Oliveira, C. and Foresti, F., 2012. A comparative structural cytogenetic study in three allopatric populations of (Teleostei: Characidae). Astyanax scabripinnisZoologia, vol. 29, no. 2, pp. 159-166.).

A large supernumerary or B chromosome, similar to that found in the population from Itiz stream, has been observed in several populations of A. scabripinnis (Néo et al., 2000Néo, D.M., Bertollo, L.A.C. and Moreira-Filho, O., 2000. Morphological differentiation and possible origin of B chromosomes in natural Brazilian population of (PISCES, CHARACIDAE). Astyanax scabripinnisGenetica, vol. 108, no. 3, pp. 211-215. http://dx.doi.org/10.1023/A:1004157901097. PMid:11294607.
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; Maistro et al., 2001Maistro, E.L., Oliveira, C. and Foresti, F., 2001. Cytogenetic characterization of a supernumerary chromosome segment and of B-chromosomes in (Teleostei, Characidae). Astyanax scabripinnisGenetica, vol. 110, no. 2, pp. 177-183. http://dx.doi.org/10.1023/A:1017961411614. PMid:11678508.
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; Ferro et al., 2003Ferro, D.A.M., Moreira-Filho, O. and Bertollo, L.A.C., 2003. B Chromosome polymorphism in the fish, Astyanax scabripinnis.Genetica, vol. 119, no. 2, pp. 147-153. http://dx.doi.org/10.1023/A:1026086501252. PMid:14620954.
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; Fernandes and Martins-Santos, 2005Fernandes, C.A. and Martins-Santos, I.C., 2005. Sympatric occurence of three cytotypes and four morphological types of B chromosomes in Astyanax scabripinnis (Pisces, Characiformes) in the river Ivaí basin, state Paraná, Brasil. Genetica, vol. 124, pp. 301-306.; Santos et al., 2012Santos, N.M., Ferreira-Neto, M., Artoni, R.F., Vicari, M.R., Bakkali, M., Oliveira, C. and Foresti, F., 2012. A comparative structural cytogenetic study in three allopatric populations of (Teleostei: Characidae). Astyanax scabripinnisZoologia, vol. 29, no. 2, pp. 159-166.). The first approach on the probable origin of this chromosome was performed by Salvador and Moreira-Filho (1992)SALVADOR, L.B. and MOREIRA-FILHO, O. (1992). B chromosomes in Astyanax scabripinnis (Pisces, Characidae). Heredity, vol. 69, pp. 50-56., who considered that a non-disjunction, followed by heterochromatinization, could be associated with its emergence. However strong evidence that this supernumerary is an isochromosome was given by some additional mitotic and meiotic studies, which also indicated that its heterochromatic nature is related with the amplification and dispersion of highly repetitive sequences (Mestriner et al., 2000MESTRINER, C.A., GALETTI, P.M., Valentini, S.R., RUIZ, I.R.G., ABEL, L.D.S., MOREIRA-FILHO, O. and CAMACHO, J.P.M., 2000. Structural and functional evidence that a B chromosome in the characid fish Astyanax scabripinnis is an isochromosome. Heredity, vol. 85, no. 1, pp. 1-9.; Moreira-Filho et al., 2004Moreira-Filho, O., Galetti Junior, P.M. and Bertollo, L.A.C., 2004. B chromosomes in the fish (Characidae, Tetragonopterinae): An overview in natural populations. Astyanax scabripinnisCytogenetic and Genome Research, vol. 106, no. 2-4, pp. 230-234. http://dx.doi.org/10.1159/000079292. PMid:15292596.
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).

Astyanax asuncionensis and Astyanax aff. bimaculatus showed the same diploid number (2n=50) but with differences in the karyotype formulas, probably due to rearrangements such as pericentric inversions. This last group, unlike the “scabripinnis group”, has shown a constancy in the diploid number (Domingues et al., 2007Domingues, M.S., Vicari, M.R., Abilhoa, V., Wanser, J.P., Cestari, M.M., Bertollo, L.A.C., Almeida, M.C. and Artoni, R.F., 2007. Cytogenetic and comparative morphology of two allopatric populations of Garutti & Britski, 2000 (Teleostei: Characidae) from upper rio Paraná basin. Astyanax altiparanaeNeotropical Ichthyology, vol. 51, no. 1, pp. 37-44.; Pamponet et al., 2008Pamponet, V.C., Carneiro, P.L., Affonso, P.R., Miranda, V.S., Silva JUNIOR, J.C., Oliveira, C.G. and Gaiotto, F.A., 2008. A multi-approach analysis of the genetic diversity in populations of aff. Linnaeus, 1758 (Teleostei: Characidae) from Northeastern Brazil. AstyanaxbimaculatusNeotropical Ichthyology, vol. 6, no. 4, pp. 621-630. http://dx.doi.org/10.1590/S1679-62252008000400010.
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; Ferreira Neto et al., 2009FERREIRA NETO, M.F., Vicari, M.R., Camargo, E.F., Artoni, R.F. and Moreira-Filho, O., 2009. Comparative cytogenetics among populations of Astyanax altiparanae (Characiformes, Characidae, Incertae sedis). Genetics and Molecular Biology, vol. 32, no. 4, pp. 792-796. http://dx.doi.org/10.1590/S1415-47572009005000078. PMid:21637456.
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; Kavalco et al., 2011Kavalco, K.F., Pazza, R., Brandão, K.O., Garcia, L.F. and Almeida-Toledo, L.F., 2011. Comparative cytogenetics and molecular phylogeography in the group – aff. . Astyanax altiparanaeAstyanaxbimaculatus (Teleostei, Characidae)Cytogenetic and Genome Research, vol. 134, no. 2, pp. 108-119. http://dx.doi.org/10.1159/000325539. PMid:21447941.
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; Pacheco et al., 2011Pacheco, R.B., Rosa, R., Giuliano-Caetano, L., Júlio-Júnior, H.F. and Dias, A.L., 2011. Cytogenetic comparison between two allopatric populations of Astyanax altiparanae Garutti et Britski, 2000 (Teleostei, Characidae), with emphasis on the localization of 18S and 5S rDNA. Comparative Cytogenetics, vol. 5, no. 3, pp. 237-246. http://dx.doi.org/10.3897/compcytogen.v5i3.1235. PMid:24260632.
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; Peres et al., 2011PERES, W.A.M., BUCKUP, P.A., BLANCO, D.R., KANTEK, D.L.Z. and MOREIRA-FILHO, O., 2011. Invasion, dispersion and hybridization of fish associated to river transposition: karyotypic evidence in “bimaculatus group” (Characiformes: Characidae). AstyanaxReviews in Fish Biology and Fisheries, vol. 1, pp. 1-8.; Martinez et al., 2012Martinez, E.R.M., Alves, A.L., Silveira, S.M., Foresti, F. and Oliveira, C., 2012. Cytogenetic analysis in the species Garutti and Britzki, 2000 and . incertae sedisAstyanax altiparanaeHyphessobrycon eques Steindachner, 1882 (Characiformes, Characidae) from the upper Paraná river basinComparative Cytogenetics, vol. 6, no. 1, pp. 41-51. http://dx.doi.org/10.3897/compcytogen.v6i1.1873. PMid:24260651.
http://dx.doi.org/10.3897/compcytogen.v6...
), indicating an evolutionary karyotype pattern relatively more conserved than that of the “scabripinnis complex”. In turn, the distinct karyotypes presented by the two populations of A. asuncionensis also show the occurrence of two karyomorphs and a probable “asuncionensis complex.” Reinforcing this hypothesis, Desordi et al., (2011)Desordi, R., Reis, D.G.S., Kavalko, K.F. and Pazza, R., 2011. Variabilidade morfológica e estruturação populacional de lambaris do grupo . Astyanax aff. bimaculatus (Teleostei, Characiformes)Evolução e Conservação da Biodiversidade, vol. 2, pp. 73-78. found that populations of A. asuncionensis from Paraguay basin although inhabiting the same river system, show diversity in the population structure and in morphological features, indicating to be very different from each other.

Astyanax has also shown a wide variation in the of distribution of the constitutive heterochromatin in the chromosomes. While the “scabripinnis complex” has been characterized by a preferential centromeric and telomeric pattern of C-bands (Fernandes and Martins-Santos, 2005Fernandes, C.A. and Martins-Santos, I.C., 2005. Sympatric occurence of three cytotypes and four morphological types of B chromosomes in Astyanax scabripinnis (Pisces, Characiformes) in the river Ivaí basin, state Paraná, Brasil. Genetica, vol. 124, pp. 301-306.; Souza et al., 2007Souza, I.L., Venere, P.C. and Moreira-Filho, O., 2007. Constitutive Heterochromatin and Ag-NOR polymorphism in the small characid fish (Jenyns, 1842). Astyanax scabripinnisCytologia, vol. 72, no. 1, pp. 63-69. http://dx.doi.org/10.1508/cytologia.72.63.
http://dx.doi.org/10.1508/cytologia.72.6...
; Santos et al., 2012Santos, N.M., Ferreira-Neto, M., Artoni, R.F., Vicari, M.R., Bakkali, M., Oliveira, C. and Foresti, F., 2012. A comparative structural cytogenetic study in three allopatric populations of (Teleostei: Characidae). Astyanax scabripinnisZoologia, vol. 29, no. 2, pp. 159-166.), the “bimaculatus group” has shown mainly interstitial heterochromatic blocks on the chromosomes (Domingues et al., 2007Domingues, M.S., Vicari, M.R., Abilhoa, V., Wanser, J.P., Cestari, M.M., Bertollo, L.A.C., Almeida, M.C. and Artoni, R.F., 2007. Cytogenetic and comparative morphology of two allopatric populations of Garutti & Britski, 2000 (Teleostei: Characidae) from upper rio Paraná basin. Astyanax altiparanaeNeotropical Ichthyology, vol. 51, no. 1, pp. 37-44.; Hashimoto et al., 2008HASHIMOTO, D.T., GONÇALVES, V.R., BORTOLOZZI, J., FORESTI, F. and PORTO-FORESTI, F., 2008. First reporto f a B chromosome in a natural population Astyanax altiparanae (Characiformes, Characidae). Genetics and Molecular Biology, vol. 31, no. 1(Suppl.), pp. 275-278.; Ferreira Neto et al., 2009FERREIRA NETO, M.F., Vicari, M.R., Camargo, E.F., Artoni, R.F. and Moreira-Filho, O., 2009. Comparative cytogenetics among populations of Astyanax altiparanae (Characiformes, Characidae, Incertae sedis). Genetics and Molecular Biology, vol. 32, no. 4, pp. 792-796. http://dx.doi.org/10.1590/S1415-47572009005000078. PMid:21637456.
http://dx.doi.org/10.1590/S1415-47572009...
; Kavalco et al., 2011Kavalco, K.F., Pazza, R., Brandão, K.O., Garcia, L.F. and Almeida-Toledo, L.F., 2011. Comparative cytogenetics and molecular phylogeography in the group – aff. . Astyanax altiparanaeAstyanaxbimaculatus (Teleostei, Characidae)Cytogenetic and Genome Research, vol. 134, no. 2, pp. 108-119. http://dx.doi.org/10.1159/000325539. PMid:21447941.
http://dx.doi.org/10.1159/000325539...
). The species now analyzed show that the distribution of heterochromatin falls, in general, among the above cases. Notably, all species showed C-positive bands in the centromeric and telomeric regions, in addition to some interstitial markings, with very conspicuous C-bands in some chromosome pairs. However, A. asuncionensis was the species with more evident interstitial heterochromatic regions, thus in this way differing from the pattern showed by Astyanax aff. paranae and Astyanax aff. bimaculatus.

As occur with C-bands, the genus Astyanax also shows distinct patterns in relation to NORs, with single and multiple systems and with both intra- and inter-specific variations in number and locations on the chromosomes (Kavalco and Moreira-Filho, 2003Kavalco, K.L. and Moreira-Filho, O., 2003. Cytogenetical analyses in four species of the genus . Astyanax (Pisces, Characidae) from Paraíba do Sul River BasinCaryologia, vol. 56, no. 4, pp. 453-461. http://dx.doi.org/10.1080/00087114.2003.10589358.
http://dx.doi.org/10.1080/00087114.2003....
; Pazza et al., 2006Pazza, R., Kavalco, K.F. and Bertollo, L.A.C., 2006. Chromosome polymorphism in (Teleostei,Characidae). 1. Karyotypic analysis, Ag-NORs and mapping of the 18S and 5S ribosomal genes in sympatric karyotypes and their possible hybrid forms. Astyanax fasciatusCytogenetic and Genome Research, vol. 112, no. 3-4, pp. 313-319. http://dx.doi.org/10.1159/000089886. PMid:16484788.
http://dx.doi.org/10.1159/000089886...
; Capistano et al., 2008CAPISTANO, T.G., PORTELA-CASTRO, A.L.B. and JULIO-JUNIOR, H.F., 2008. Chromosome divergence and NOR polymorphism in Bryconamericus aff. iheringii (Teleostei, Characidae) in the hydrographic systems of the Paranapanema and Ivaí Rivers, Paraná, Brazil. Genetics and Molecular Biology, vol. 31, no. 1 (Suppl), pp. 203-207.; Kavalco et al., 2011Kavalco, K.F., Pazza, R., Brandão, K.O., Garcia, L.F. and Almeida-Toledo, L.F., 2011. Comparative cytogenetics and molecular phylogeography in the group – aff. . Astyanax altiparanaeAstyanaxbimaculatus (Teleostei, Characidae)Cytogenetic and Genome Research, vol. 134, no. 2, pp. 108-119. http://dx.doi.org/10.1159/000325539. PMid:21447941.
http://dx.doi.org/10.1159/000325539...
). In this study a multiple marking system was only found in Astyanax aff. bimaculatus. The other species showed only one pair of submetacentric chromosomes with NOR sites on the short arms. In this sense, A. aff. bimaculatus showed a divergent karyotype concerning to these chromosomal markers in comparison to the other species investigated.

The data obtained contribute to the knowledge of the existing biodiversity in the genus Astyanax, here evidenced by chromosomal characteristics of the species studied. In addition to evidence some aspects on the chromosome evolution in this fish group, indications about possible complexes of species in Astyanax aff. paranae and A. asuncionensis were also obtained. The biodiversity in Astyanax may be related to the biological characteristics of these fishes. Indeed, the possibility in forming small populations can favor the fixation of chromosome changes, both in the macro- as in the microstructure of the chromosomes.

Acknowledgements

The authors thank CNPq for financial support and Dr. Weferson Junio da Graça (UEM) for species identification.

  • (With 3 Figures)

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Publication Dates

  • Publication in this collection
    01 Mar 2016
  • Date of issue
    Apr-Jun 2016

History

  • Received
    18 Aug 2014
  • Accepted
    24 Feb 2015
Instituto Internacional de Ecologia R. Bento Carlos, 750, 13560-660 São Carlos SP - Brasil, Tel. e Fax: (55 16) 3362-5400 - São Carlos - SP - Brazil
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