Cytogenetics of Gymnogeophagus setequedas (Cichlidae: Geophaginae), with comments on its geographical distribution

Leonardo M. Paiz Lucas Baumgärtner Weferson J. da Graça Vladimir P. Margarido Carla S. Pavanelli About the authors

ABSTRACT

We provide cytogenetic data for the threatened species Gymnogeophagus setequedas, and the first record of that species collected in the Iguaçu River, within the Iguaçu National Park’s area of environmental preservation, which is an unexpected occurrence for that species. We verified a diploid number of 2n = 48 chromosomes (4sm + 24st + 20a) and the presence of heterochromatin in centromeric and pericentromeric regions, which are conserved characters in the Geophagini. The multiple nucleolar organizer regions observed in G. setequedas are considered to be apomorphic characters in the Geophagini, whereas the simple 5S rDNA cistrons located interstitially on the long arm of subtelocentric chromosomes represent a plesiomorphic character. Because G. setequedas is a threatened species that occurs in lotic waters, we recommend the maintenance of undammed environments within its known area of distribution.

Keywords:
Chromosomes; Conservation; Iguaçu River; Karyotype; Paraná River

RESUMO

Fornecemos dados citogenéticos para a espécie ameaçada Gymnogeophagus setequedas, e o primeiro registro da espécie coletado no rio Iguaçu, na área de preservação ambiental do Parque Nacional do Iguaçu, a qual é uma área de ocorrência inesperada para esta espécie. Verificamos em G. setequedas 2n = 48 cromossomos (4sm + 24st + 20a) e heterocromatina presente nas regiões centroméricas e pericentroméricas, as quais indicam caracteres conservados em Geophagini. Múltiplas regiões organizadoras de nucléolos foram observadas em G. setequedas e são consideradas características apomórficas em Geophagini, enquanto cístrons de DNAr 5S simples e localizados intersticialmente no braço longo de cromossomos subtelocêntricos representam uma característica plesiomórfica. Visto que G. setequedas é uma espécie ameaçada de extinção que ocorre em águas lóticas, recomendamos a manutenção de ambientes livre de barragens em sua área de distribuição.

Palavras-chave:
Cariótipo; Conservação; Cromossomos; Rio Iguaçu; Rio Paraná

Introduction

Neotropical cichlids are arranged in seven tribes (Sparks, Smith, 2004Sparks JS, Smith WL. Phylogeny and biogeography of cichlid fishes (Teleostei: Perciformes: Cichlidae). Cladistics. 2004; 20(6):501-17.; Smith et al., 2008Smith WL, Chakrabarty P, Sparks JS. Phylogeny, taxonomy, and evolution of neotropical cichlids (Teleostei: Cichlidae: Cichlinae). Cladistics. 2008; 24(5):625-41.), including Geophagini. Within that tribe, Gymnogeophagus Miranda Ribeiro, 1918 can be diagnosed by two apomorphic traits, the absence of a supraneural bone and the presence of a forward-facing spine of the first dorsal pterygiophore (Reis, Malabarba, 1987Reis RE, Malabarba LR. Revision of the Neotropical genus Gymnogeophagus Ribeiro, 1918 with descriptions of two new species (Pisces, Perciformes). Rev Bras Zool. 1987; 4(4):259-305.). Gymnogeophagus currently comprises 17 species, distributed in the Paraná, Paraguay and Uruguay River basins, as well as the coastal basins of southern Brazil and Uruguay (Kullander, 2003Kullander SO. Family Cichlidae (Cichlids). In: Reis RE, Kullander SO, Ferraris CJ, Jr., organizers. Check list of the freshwater fishes of South and Central America. Porto Alegre: Edipucrs; 2003. p.605-654.; González-Bergonzoni et al., 2009González-Bergonzoni I, Loureiro M, Oviedo S. A new species of Gymnogeophagus from the río Negro and río Tacuarí basins, Uruguay (Teleostei: Perciformes). Neotrop Ichthyol. 2009; 7(1):19-24.; Malabarba et al., 2015Malabarba LR, Malabarba MC, Reis RE. Descriptions of five new species of the Neotropical cichlid genus Gymnogeophagus Miranda Ribeiro, 1918 (Teleostei: Cichliformes) from the rio Uruguay drainage. Neotrop Ichthyol . 2015; 13(4):637-62.; Loureiro et al., 2016Loureiro M, Zarucki M, Malabarba LR, González-Bergonzoni I. A new species of Gymnogeophagus Miranda Ribeiro from Uruguay (Teleostei: Cichliformes). Neotrop Ichthyol . 2016; 14(1):155-64.). Gymnogeophagus setequedas is the only species of that genus considered threatened in all the Brazilian red lists.

Reis et al. (1992Reis RE, Malabarba LR, Pavanelli CS. Gymnogeophagus setequedas, a new cichlid species (Teleostei: Labroidei) from middle rio Paraná system, Brazil and Paraguay. Ichthyol Explor Freshw. 1992; 3(3):265-72.) described Gymnogeophagus setequedas based on 91 specimens collected in Paraguayan rivers and six from a tributary on the Brazilian margin of the Itaipu Reservoir. Since this description, there have been a number of unsuccessful attempts to collect new specimens from within the known geographical range of the species (Agostinho et al., 2004Agostinho AA, Thomaz SM, Gomes LC. Threats for biodiversity in the floodplain of the Upper Paraná River: effects of hydrological regulation by dams. Ecohydrol Hydrobiol. 2004; 4(3):255-68.; Pavanelli, Reis, 2008Pavanelli CS, Reis RE. Gymnogeophagus setequedas. In: Machado ABM, Drummond GM, Paglia AP, editores. Livro vermelho da fauna brasileira ameaçada de extinção. Brasília: Fundação Biodiversitas; 2008. p.184-186.). However, during a recent evaluation of the material deposited in the ichthyological collection of the Museu de Ciências e Tecnologia of the Pontifícia Universidade Católica do Rio Grande do Sul (MCP) (Porto Alegre, Brazil), eight specimens of G. setequedas were identified. These specimens were collected in the Iguaçu River, approximately 200 km from the type locality (Iguazú River at Juan E. O’Leary, Paraguay). More recently, surveys conducted both up and downstream from the Iguaçu Falls in the Iguaçu National Park resulted in the collection of 15 specimens of G. setequedas.

The fish fauna of the Iguaçu River is highly endemic, due to the presence of the Iguaçu Falls, which form a natural barrier to the dispersal of fish, and includes areas of endemism within the river’s lower basin (Vera-Alcaraz et al., 2009bVera-Alcaraz HS, Pavanelli CS, Bertaco VA. Astyanax jordanensis (Ostariophysi: Characidae), a new species from the rio Iguaçu basin, Paraná, Brazil. Neotrop Ichthyol . 2009b; 7(2):185-90.). In this case, the occurrence of G. setequedas upstream from the falls was unexpected. For instance, Baumgartner et al. (2012Baumgartner G, Pavanelli CS, Baumgartner D, Bifi AG, Debona T, Frana VA. Peixes do Baixo Rio Iguaçu. Maringá: Eduem; 2012.), who published a catalog of the fish of the lower Iguaçu River basin, did not register the occurrence of G. setequedas in that region.

Abilhoa, Duboc (2004Abilhoa V, Duboc LF. Peixes. In: Mikich SB, Bérnils RS, editores. Livro vermelho da fauna ameaçada no estado do Paraná. Curitiba: Instituto Ambiental do Paraná; 2004. p.581-677.) included Gymnogeophagus setequedas among the threatened species of the Brazilian state of Paraná, using its restricted distribution and reduction in its available habitat as justification. Pavanelli, Reis (2008Pavanelli CS, Reis RE. Gymnogeophagus setequedas. In: Machado ABM, Drummond GM, Paglia AP, editores. Livro vermelho da fauna brasileira ameaçada de extinção. Brasília: Fundação Biodiversitas; 2008. p.184-186.) subsequently included G. setequedas in the Brazilian red list of endangered species, and it has been listed as Vulnerable (VU) by the International Union for Conservation of Nature (IUCN). In a subsequent review of the Brazilian list (decree #445 in the Official Federal Gazette of December 17, 2014), the Brazilian Environmental Ministry raised the status of the species to Endangered (EN). Vera-Alcaraz et al. (2009aVera-Alcaraz HS, Morlis WG, Reis RE. Gymnogeophagus setequedas. UICN-GUYRA-PROTEGER. Uso Sostenible de Peces en la Cuenca del Plata [Internet]. [updated 2009a; cited 2017 Mar 14). Available from: Available from: http://www.proteger.org/peces-cuenca-plata/especies/gymnogeophagus-setequedas/
http://www.proteger.org/peces-cuenca-pla...
) also listed G. setequedas as Endangered (EN) in Paraguay.

The unexpected discovery and collection of new specimens of this species also provided an opportunity to expand cytogenetic knowledge of Geophagini. Previous cytogenetic data are available for species of the genera Geophagus Heckel, 1840 (Vicari et al., 2006Vicari MR, Artoni RF, Moreira-Filho O, Bertollo LAC. Basic and molecular cytogenetics in freshwater Cichlidae (Osteichthyes, Perciformes) Karyotypic conservationism and divergence. Caryologia. 2006; 59(3):260-66.; Pires et al., 2010Pires LB, Giuliano-Caetano L, Dias AL. Cytogenetic characterization of Geophagus brasiliensis and two species of Gymnogeophagus (Cichlidae: Geophaginae) from Guaíba Lake, RS, Brazil. Folia Biol. 2010; 58(1-2):29-34.; Nakajima et al., 2012Nakajima RT, Cabral-de-Mello DC, Valente GT, Venere PC, Martins C. Evolutionary dynamics of rRNA gene clusters in cichlid fish. BMC Evol Biol. 2012; 12:198-222.; Schneider et al., 2013Schneider CH, Gross MC, Terencio ML, Artoni RF, Vicari MR, Martins C, Feldberg E. Chromosomal evolution of Neotropical cichlids: the role of repetitive DNA sequences in the organization and structure of karyotype. Rev Fish Biol Fisher. 2013; 23(2):201-14.; Perazzo et al., 2013Perazzo GX, Noleto RB, Vicari MR, Gava A, Cestari MM. Trends of karyotypical evolution in the pearl cichlid, Geophagus brasiliensis, from southern Brazil. Zoology. 2013; 116(5):286-92.), Gymnogeophagus Miranda Ribeiro, 1918 (Pires et al., 2010Pires LB, Giuliano-Caetano L, Dias AL. Cytogenetic characterization of Geophagus brasiliensis and two species of Gymnogeophagus (Cichlidae: Geophaginae) from Guaíba Lake, RS, Brazil. Folia Biol. 2010; 58(1-2):29-34.), Apistogramma Regan, 1913, Biotodoma Eigenmann & Kennedy, 1903 and Satanoperca Günther, 1862 (Poletto et al., 2010aPoletto AB, Ferreira IA, Cabral-de-Mello DC, Nakajima RT, Mazzuchelli J, Ribeiro HB, Venere PC, Nirchio M, Kocher TD, Martins C. Chromosome differentiation patterns during cichlid fish evolution. BMC Genet. 2010a; 11:50-61.). In the case of Gymnogeophagus, cytogenetic studies have focused on just three species, G. balzanii (Feldberg, Bertollo, 1984Feldberg E, Bertollo LAC. Discordance in chromosome number among somatic and gonadal tissue cells of Gymnogeophagus balzanii (Pisces, Cichlidae). Brazil J Genet . 1984; 7(4):639-45., 1985aFeldberg E, Bertollo LAC. Karyotypes of 10 species of Neotropical Cichlids (Pisces, Perciformes). Caryologia. 1985a; 38(3-4):257-68.; Roncati et al., 2007Roncati HA, Pastori MC, Fenocchio AS. Cytogenetic studies and evolutive considerations on fishes of the family Cichlidae (Perciformes) from Parana River (Argentina). Cytologia. 2007; 72(4):379-84.), G. gymnogenys and G. labiatus (Pires et al., 2010Pires LB, Giuliano-Caetano L, Dias AL. Cytogenetic characterization of Geophagus brasiliensis and two species of Gymnogeophagus (Cichlidae: Geophaginae) from Guaíba Lake, RS, Brazil. Folia Biol. 2010; 58(1-2):29-34.). These species have a diploid number of 48 chromosomes, a centromeric/pericentromeric distribution of heterochromatin, and simple nucleolar organizer regions (NORs), located predominantly on the first chromosome pair. However, the cytogenetics of G. setequedas has been unknown.

In this study, we present the first basic and molecular cytogenetic data for G. setequedas, as well as the 5S and 18S rDNA-FISH for the genus as a whole. We also discuss the recent expansion of the known geographical distribution of G. setequedas and the implications of that discovery on its current conservation status.

Material and Methods

Fifteen specimens of Gymnogeophagus setequedas were analyzed for cytogenetic characters, comprising six females, six males and three specimens of unidentified sex. The sex determination was made by microscopic analysis of the gonads. Specimens were captured in the Iguaçu River upstream (25°37’13.20″S/54°23’29.20″W: NUP 14913 (6) and NUP 15962 (5)) and downstream from the Iguaçu Falls (25°38’18.72″S/54°28’4.74″W: NUP 14919 (3) and NUP 14933 (1)) (Fig. 1). Two additional lots MCP 22632 (8) and NUP 3122 (6) were verified as G. setequedas and plotted on the map to help document the geographic expansion of the species. Institutional abbreviations are: MCP, Museu de Ciências e Tecnologia of the Pontifícia Universidade Católica do Rio Grande do Sul, Porto Alegre, and NUP, Coleção Ictiológica do Núcleo de Pesquisas em Limnologia, Ictiologia e Aquicultura of the Universidade Estadual de Maringá, Maringá.

Fig. 1
Partial map of southern South America showing distribution of Gymnogeophagus setequedas. Yellow symbols represent lots of specimens from type-material and additional material housed in Swedish Museum of Natural History. The yellow star marks the type-locality (río Iguazú Reservoir, at Juan E. O’Leary, Paraná River basin, Paraguay). Red squares represent the new specimens discovered from the Iguaçu River basin, Brazil. White lines indicate physical barriers to dispersal.

The study was carried out in strict accordance with the recommendations of the Guide for the Care and Use of Laboratory Animals, approved by the Committee on the Ethics of Animal Experiments of the Universidade Estadual do Oeste do Paraná (License Number: Protocol 13/09 - CEEAAP/Unioeste). Individuals were sacrificed with an overdose of clove oil, following Griffiths (2000Griffiths SP. The use of clove oil as an anesthetic and method for sampling intertidal rockpool fishes. J Fish Biol. 2000; 57(6):1453-64.). Mitotic chromosomes were obtained from kidney cells by direct method of air-drying according to Bertollo et al. (1978Bertollo LAC, Takahashi CS, Moreira-Filho O. Cytotaxonomic considerations on Hoplias lacerdae (Pisces, Erythrinidae). Brazil J Genet. 1978; 1:103-20.). Methodologies for detection of NORs by silver impregnation (AgNORs) and heterochromatic regions by technique of barium hydroxide (C-band) followed the protocols of Howell, Black (1980Howell WM, Black DA. Controlled silver staining of nucleolus organizer regions with a protective colloidal developer: a 1-step method. Experientia. 1980; 36(8):1014-15.) and Sumner (1972Sumner AT. A simple technique for demonstrating centromeric heterochromatin. Exp Cell Res. 1972; 75(1):304-06.), respectively, with modifications in the step coloration suggested by Lui et al. (2012Lui RL, Blanco DR, Moreira-Filho O, Margarido VP. Propidium iodide for making heterochromatin more evident in the C-banding technique. Biotech & Histochem. 2012; 87(7):433-38.). Physical mapping of 5S rDNA and 18S rDNA sequences was carried out by fluorescence in situ hybridization (FISH) in accordance with Pinkel et al. (1986Pinkel D, Straume T, Gray JW. Cytogenetic analysis using quantitative, high-sensitivity, fluorescence hybridization. Proc Natl Acad Sci. 1986; 83(9):2934-38.) and modifications suggested by Margarido, Moreira-Filho (2008Margarido VP, Moreira-Filho O. Karyotypic differentiation through chromosome fusion and number reduction in Imparfinis hollandi (Ostariophysi, Heptapteridae). Genet Mol Biol. 2008; 31(1):235-38.), with probes obtained from Megaporinus elongatus (Valenciennes, 1850) (Martins, Galetti, 1999Martins C, Galetti PM, Jr. Chromosomal localization of 5S rDNA genes in Leporinus fish (Anostomidae, Characiformes). Chromosome Res. 1999; 7(5):363-67.) and Prochilodus argenteus Spix & Agassiz, 1829 (Hatanaka, Galetti, 2004Hatanaka T, Galetti PM, Jr. Mapping of the 18S and 5S ribosomal RNA genes in the fish Prochilodus argenteus Agassiz, 1829 (Characiformes, Prochilodontidae). Genetica. 2004; 122(3):239-44.), respectively. The 5S rDNA probe was labeled with digoxigenin-11-dUTP (Dig Nick Translation Kit - Roche®, Basel, BS, Switzerland) and the 18S rDNA probe was labeled with biotin-16-dUTP (Biotin Nick Translation Kit - Roche®). Each probe was dissolved at a concentration of 3 ng/µl in a hybridization mixture (50% formamide, 2xSSC, 10% dextran sulfate). Hybridization was carried out in a wet chamber at 37ºC for approximately 16 hours. To detect the signal, the protocol used amplified antidigoxigenina-rhodamine (Roche®) for the 5S rDNA probe and avidin-FITC with anti-avidin biotinylated (Sigma-Aldrich, Buchs, SG, Switzerland) for the 18S rDNA probe. Chromosomes were subsequently counterstained with 4’,6-diamidino-2-phenylindol (DAPI) at a concentration of 50 µg/ml. The software DP Controller 3.2.1.276 was used with an Olympus DP 71 digital camera attached to an epifluorescence microscope BX 61 (Olympus America Inc., Center Valley, PA, United States of America) to photograph the slides. To organize the karyotype, we calculated the relation of the arms as proposed by Levan et al. (1964Levan A, Fredga K, Sandberg AA. Nomenclature for centromeric position on chromosomes. Hereditas. 1964; 52(2):201-20.).

We also compiled chromosomal data for Cichlidae from this and prior studies, and present those data in a phylogenetic context at the level of genera and in tabular format at the level of species (Tab. 1). Chromosomal data presented for the genera were chosen preferentially for the species included in Smith et al. (2008Smith WL, Chakrabarty P, Sparks JS. Phylogeny, taxonomy, and evolution of neotropical cichlids (Teleostei: Cichlidae: Cichlinae). Cladistics. 2008; 24(5):625-41.), when chromosomal data for these species were available. Otherwise, we chose a species with the most common chromosomal pattern to represent the genus.

Tab. 1
Compilation of cytogenetic data including karyotype formulae, 18S and 5S rDNA for Malagasy, Indian, African and Neotropical cichlid species. 2n = diploid number; m = metacentric; sm = submetacentric; st = subtelocentric; a = acrocentric; p = short arm; q = long arm; t = terminal position; i = interstitial position; c = centromeric position; chr = chromosomes. References: (1) Nakajima et al. (2012Nakajima RT, Cabral-de-Mello DC, Valente GT, Venere PC, Martins C. Evolutionary dynamics of rRNA gene clusters in cichlid fish. BMC Evol Biol. 2012; 12:198-222.); (2) Paiz et al. (2014Paiz LM, Baumgartner L, Moresco RM, Treco FR, da Graça WJ, Margarido VP. Evolutionary and biogeographical approach on Australoheros angiru (Cichlidae) from lagoons in a dividing plateau between the basins of the Iguassu River and the Uruguay River, Brazil. Rev Fish Biol Fisher. 2014; 24(1):399-407.); (3) Perazzo et al. (2011Perazzo GX, Noleto RB, Vicari MR, Machado PC, Gava A, Cestari MM. Chromosomal studies in Crenicichla lepidota and Australoheros facetus (Cichlidae, Perciformes) from extreme Southern Brazil. Rev Fish Biol Fish. 2011; 21(3):509-15.); (4) Poletto et al. (2010aPoletto AB, Ferreira IA, Cabral-de-Mello DC, Nakajima RT, Mazzuchelli J, Ribeiro HB, Venere PC, Nirchio M, Kocher TD, Martins C. Chromosome differentiation patterns during cichlid fish evolution. BMC Genet. 2010a; 11:50-61.); (5) Poletto et al . (2010bPoletto AB, Ferreira IA, Martins C. The B chromosomes of the African cichlid fish Haplochromis obliquidens harbour 18S rRNA gene copies. BMC Genet . 2010b; 11:1-8.); (6) Schneider et al. (2013Schneider CH, Gross MC, Terencio ML, Artoni RF, Vicari MR, Martins C, Feldberg E. Chromosomal evolution of Neotropical cichlids: the role of repetitive DNA sequences in the organization and structure of karyotype. Rev Fish Biol Fisher. 2013; 23(2):201-14.); (7) Vicari et al. (2006Vicari MR, Artoni RF, Moreira-Filho O, Bertollo LAC. Basic and molecular cytogenetics in freshwater Cichlidae (Osteichthyes, Perciformes) Karyotypic conservationism and divergence. Caryologia. 2006; 59(3):260-66.). Classification used follows Smith et al. (2008Smith WL, Chakrabarty P, Sparks JS. Phylogeny, taxonomy, and evolution of neotropical cichlids (Teleostei: Cichlidae: Cichlinae). Cladistics. 2008; 24(5):625-41.).

Results

We verified a diploid number of 48 chromosomes (4sm + 24st + 20a) for Gymnogeophagus setequedas and observed no differences in karyotype macrostructure either between sexes or between up- and downstream populations (Fig. 2a). The silver impregnation revealed multiple NORs located terminally on the long arm of the subtelocentric chromosome pair 8 and on one of the acrocentric chromosomes of pair 20 (Fig. 2a, in box). Heterochromatin was observed in centromeric/pericentromeric positions in most chromosomes, where it coincided with rDNA sites (Fig. 2b). The 18S rDNA-FISH confirmed the findings of the silver impregnation in both homologous chromosomes of pairs 8 and 20, in addition to highlighting cistrons in the terminal region of the long arm of one of the acrocentric chromosomes of pair 24 (Fig. 2c). The 5S rDNA-FISH revealed cistrons in the interstitial region of the long arm of the subtelocentric chromosome pair 4 (Fig. 2c).

Fig. 2
Karyotypes of Gymnogeophagus setequedas: a. Giemsa stained; b. C-banded; and c. after fluorescence in situ hybridization with 5S rDNA probe (rhodamine, red) and 18S rDNA probe (FITC, green). NORs bearing chromosomes are boxed in Ag-stained (AgNORs). Scales bar = 5 µm.

Discussion

Cytogenetic analyses and tendencies of chromosome evolution in the Cichlidae. The diploid number of 48 chromosomes found in Gymnogeophagus setequedas is the same as the number observed in congeneric species. However, the karyotype formula for G. setequedas (4sm + 24st + 20a) differs from those of its congeners, such as G. balzanii (2m-sm + 46st-a, Roncati et al., 2007Roncati HA, Pastori MC, Fenocchio AS. Cytogenetic studies and evolutive considerations on fishes of the family Cichlidae (Perciformes) from Parana River (Argentina). Cytologia. 2007; 72(4):379-84.), G. gymnogenys (4m + 44st-a; 6m + 42st-a), and G. labiatus (4m + 4sm + 40st-a) (Pires et al., 2010Pires LB, Giuliano-Caetano L, Dias AL. Cytogenetic characterization of Geophagus brasiliensis and two species of Gymnogeophagus (Cichlidae: Geophaginae) from Guaíba Lake, RS, Brazil. Folia Biol. 2010; 58(1-2):29-34.). These differences may reflect structural rearrangements, such as inversions and/or translocations, or may be due to the condensation or reorganization of the chromosomes, as proposed by the respective authors. Similar karyotype formulae have also been found in most other geophagin genera, such as Geophagus brasiliensis (6sm + 42st, Vicari et al., 2006Vicari MR, Artoni RF, Moreira-Filho O, Bertollo LAC. Basic and molecular cytogenetics in freshwater Cichlidae (Osteichthyes, Perciformes) Karyotypic conservationism and divergence. Caryologia. 2006; 59(3):260-66.; 4sm + 44st, Pires et al., 2010Pires LB, Giuliano-Caetano L, Dias AL. Cytogenetic characterization of Geophagus brasiliensis and two species of Gymnogeophagus (Cichlidae: Geophaginae) from Guaíba Lake, RS, Brazil. Folia Biol. 2010; 58(1-2):29-34.), Biotodoma cupido (4m-sm + 44st-a) and Satanoperca jurupari (4m-sm + 44st-a) (Poletto et al., 2010aPoletto AB, Ferreira IA, Cabral-de-Mello DC, Nakajima RT, Mazzuchelli J, Ribeiro HB, Venere PC, Nirchio M, Kocher TD, Martins C. Chromosome differentiation patterns during cichlid fish evolution. BMC Genet. 2010a; 11:50-61.). In Apistogramma borellii, however, Poletto et al. (2010aPoletto AB, Ferreira IA, Cabral-de-Mello DC, Nakajima RT, Mazzuchelli J, Ribeiro HB, Venere PC, Nirchio M, Kocher TD, Martins C. Chromosome differentiation patterns during cichlid fish evolution. BMC Genet. 2010a; 11:50-61.) recorded a quite different arrangement (16m-sm + 30st-a). This arrangement, which includes a large number of meta-submetacentric pairs, is the most differentiated karyotype in the tribe.

Karyotype macrostructure varies considerably in other tribes of the subfamily Cichlinae, such as shown in Tab. 1. Of all the Neotropical cichlids, Smith et al. (2008Smith WL, Chakrabarty P, Sparks JS. Phylogeny, taxonomy, and evolution of neotropical cichlids (Teleostei: Cichlidae: Cichlinae). Cladistics. 2008; 24(5):625-41.) considered the Heroini as the apical tribe within the Cichlinae (Fig. 3). A diploid set of 48 subtelo-acrocentric chromosomes is considered to be the plesiomorphic condition in the Neotropical group and is observed in Cichla Schneider, 1801 (Cichlini) and Retroculus Eigenmann & Bray, 1894 (Retroculini) (Poletto et al., 2010aPoletto AB, Ferreira IA, Cabral-de-Mello DC, Nakajima RT, Mazzuchelli J, Ribeiro HB, Venere PC, Nirchio M, Kocher TD, Martins C. Chromosome differentiation patterns during cichlid fish evolution. BMC Genet. 2010a; 11:50-61.; Valente et al., 2012Valente GT, Vitorino CA, Cabral-de-Mello DC, Oliveira C, Souza IL, Martins C, Venere PC. Comparative cytogenetics of ten species of cichlid fishes (Teleostei, Cichlidae) from the Araguaia River system, Brazil, by conventional cytogenetic methods. Comp Cytogenet. 2012; 6(2):163-81.).

Fig. 3
Phylogeny of Malagasy, Indian, African and Neotropical cichlids showing the karyotypic formulae, 18S and 5S rDNA of a species possessing the most common cytogenetic data for each genus. m = metacentric; sm = submetacentric; st = subtelocentric; a = acrocentric; p = short arm; q = long arm; c = centromeric position; t = terminal position; i = interstitial position. The phylogeny is modified from Smith et al. (2008Smith WL, Chakrabarty P, Sparks JS. Phylogeny, taxonomy, and evolution of neotropical cichlids (Teleostei: Cichlidae: Cichlinae). Cladistics. 2008; 24(5):625-41.).

The karyotype macrostructure of G. setequedas and its congeners is similar to this ancestral model, but with more subtelo-acrocentric chromosome pairs than meta-submetacentric ones, which appears to be a conserved character in the geophagins.

Silver nitrate impregnation revealed multiple NORs in G. setequedas, a pattern also found in one population of G. gymnogenys (Pires et al., 2010Pires LB, Giuliano-Caetano L, Dias AL. Cytogenetic characterization of Geophagus brasiliensis and two species of Gymnogeophagus (Cichlidae: Geophaginae) from Guaíba Lake, RS, Brazil. Folia Biol. 2010; 58(1-2):29-34.), but with considerable differences in the NORs distribution. In G. setequedas, the NORs are present in a terminal position on the long arm of the subtelo-acrocentric pair 8 and in one acrocentric chromosome of pair 20. In G. gymnogenys, by contrast, the NORs are found in an interstitial position on the long arm of the subtelo-acrocentric chromosome pair 3 and a terminal position on the short arm of the subtelo-acrocentric pair 9 (Pires et al., 2010Pires LB, Giuliano-Caetano L, Dias AL. Cytogenetic characterization of Geophagus brasiliensis and two species of Gymnogeophagus (Cichlidae: Geophaginae) from Guaíba Lake, RS, Brazil. Folia Biol. 2010; 58(1-2):29-34.). By contrast, simple NORs were observed in an interstitial position on the short arm of the meta-submetacentric chromosome pair in G. balzanii (Roncati et al., 2007Roncati HA, Pastori MC, Fenocchio AS. Cytogenetic studies and evolutive considerations on fishes of the family Cichlidae (Perciformes) from Parana River (Argentina). Cytologia. 2007; 72(4):379-84.), G. labiatus (Pires et al., 2010Pires LB, Giuliano-Caetano L, Dias AL. Cytogenetic characterization of Geophagus brasiliensis and two species of Gymnogeophagus (Cichlidae: Geophaginae) from Guaíba Lake, RS, Brazil. Folia Biol. 2010; 58(1-2):29-34.) and B. cupido (Valente et al., 2012Valente GT, Vitorino CA, Cabral-de-Mello DC, Oliveira C, Souza IL, Martins C, Venere PC. Comparative cytogenetics of ten species of cichlid fishes (Teleostei, Cichlidae) from the Araguaia River system, Brazil, by conventional cytogenetic methods. Comp Cytogenet. 2012; 6(2):163-81.), and in a terminal position on the short arm of the subtelo-acrocentric chromosome in Geophagus brasiliensis (Vicari et al., 2006Vicari MR, Artoni RF, Moreira-Filho O, Bertollo LAC. Basic and molecular cytogenetics in freshwater Cichlidae (Osteichthyes, Perciformes) Karyotypic conservationism and divergence. Caryologia. 2006; 59(3):260-66.) and Satanoperca jurupari (Poletto et al., 2010aPoletto AB, Ferreira IA, Cabral-de-Mello DC, Nakajima RT, Mazzuchelli J, Ribeiro HB, Venere PC, Nirchio M, Kocher TD, Martins C. Chromosome differentiation patterns during cichlid fish evolution. BMC Genet. 2010a; 11:50-61.). The presence of simple NORs in the first chromosome pair (meta-submetacentric) is probably a plesiomorphic condition in Neotropical cichlids (Feldberg, Bertollo, 1985bFeldberg E, Bertollo LAC. Nucleolar organizing regions in some species of Neotropical cichlid fish (Pisces, Perciformes). Caryologia. 1985b; 38(3-4):319-24.). In this case, multiple NORs in a terminal position of the long arm of the subtelo-acrocentric pair in G. setequedas can be considered apomorphic in the Geophagini (Fig. 3), where the location of NORs on different chromosome pairs must be the result of chromosomal rearrangements such as translocations.

The specific implications of the 5S and 18S rDNA-FISH data of G. setequedas in comparison with other cichlids. Our FISH data are the first reported for Gymnogeophagus, and revealed multiple 18S rDNA cistrons similar to the Neotropical heroins Mesonauta festivus and Uaru amphiacanthoides, and the African species Haplochromis obliquidens and Oreochromis niloticus (Pseudocrenilabrinae). However, the number and position of these cistrons vary considerably among species. In G. setequedas, they are found in a terminal position on the long arms of the five subtelo-acrocentric chromosomes, whereas in H. obliquidens, M. festivus and O. niloticus these cistrons are located in a terminal position of the short arms of the subtelo-acrocentric chromosomes, in four, five and six pairs, respectively (Poletto et al., 2010aPoletto AB, Ferreira IA, Cabral-de-Mello DC, Nakajima RT, Mazzuchelli J, Ribeiro HB, Venere PC, Nirchio M, Kocher TD, Martins C. Chromosome differentiation patterns during cichlid fish evolution. BMC Genet. 2010a; 11:50-61.). In the remaining species of the Etroplinae, Pseudocrenilabrinae and Cichlinae, analyses have shown simple 18S rDNA cistrons (Poletto et al., 2010aPoletto AB, Ferreira IA, Cabral-de-Mello DC, Nakajima RT, Mazzuchelli J, Ribeiro HB, Venere PC, Nirchio M, Kocher TD, Martins C. Chromosome differentiation patterns during cichlid fish evolution. BMC Genet. 2010a; 11:50-61.), which vary in their position (terminal or interstitial) and the chromosome pairs (meta-submetacentric or subtelo- acrocentric) that bear them. Cichla monoculus (Cichlini) and Retroculus lapidifer (Retroculini) belong to basal cichline genera (Smith et al., 2008Smith WL, Chakrabarty P, Sparks JS. Phylogeny, taxonomy, and evolution of neotropical cichlids (Teleostei: Cichlidae: Cichlinae). Cladistics. 2008; 24(5):625-41.), and differ in the location of the 18S rDNA cistrons, which are found in a terminal position on the long arm of the subtelo-acrocentric chromosomes in C. monoculus (Schneider et al., 2013Schneider CH, Gross MC, Terencio ML, Artoni RF, Vicari MR, Martins C, Feldberg E. Chromosomal evolution of Neotropical cichlids: the role of repetitive DNA sequences in the organization and structure of karyotype. Rev Fish Biol Fisher. 2013; 23(2):201-14.) and in a terminal position on the short arm of the subtelo-acrocentric chromosomes in R. lapidifer (Poletto et al., 2010aPoletto AB, Ferreira IA, Cabral-de-Mello DC, Nakajima RT, Mazzuchelli J, Ribeiro HB, Venere PC, Nirchio M, Kocher TD, Martins C. Chromosome differentiation patterns during cichlid fish evolution. BMC Genet. 2010a; 11:50-61.). In Pseudetroplus maculatus (Bloch, 1795) (Etroplinae) and Hemichromis bimaculatus (Pseudocrenilabrinae), considered here as outgroups, simple 18S rDNA cistrons are located on the short arm of the subtelo-acrocentric chromosomes and represent a plesiomorphic character in the Cichlidae (Fig. 3). In G. setequedas, by comparison, multiple cistrons are found in a terminal position on the long arm, indicating that this is an apomorphic character in this species.

The simple 5S rDNA cistrons found in Gymnogeophagus setequedas were located in an interstitial position on the long arm of the subtelocentric chromosome pair 4, which is a similar configuration to that found in other geophagin species, such as Satanoperca jurupari (Nakajima et al., 2012Nakajima RT, Cabral-de-Mello DC, Valente GT, Venere PC, Martins C. Evolutionary dynamics of rRNA gene clusters in cichlid fish. BMC Evol Biol. 2012; 12:198-222.), Geophagus proximus (Schneider et al., 2013Schneider CH, Gross MC, Terencio ML, Artoni RF, Vicari MR, Martins C, Feldberg E. Chromosomal evolution of Neotropical cichlids: the role of repetitive DNA sequences in the organization and structure of karyotype. Rev Fish Biol Fisher. 2013; 23(2):201-14.) and G. brasiliensis (Vicari et al., 2006Vicari MR, Artoni RF, Moreira-Filho O, Bertollo LAC. Basic and molecular cytogenetics in freshwater Cichlidae (Osteichthyes, Perciformes) Karyotypic conservationism and divergence. Caryologia. 2006; 59(3):260-66.; Perazzo et al., 2013Perazzo GX, Noleto RB, Vicari MR, Gava A, Cestari MM. Trends of karyotypical evolution in the pearl cichlid, Geophagus brasiliensis, from southern Brazil. Zoology. 2013; 116(5):286-92.), and species from closely-related tribes, such as Cichla monoculus (Cichlini), Astronotus ocellatus (Astronotini) (Schneider et al., 2013Schneider CH, Gross MC, Terencio ML, Artoni RF, Vicari MR, Martins C, Feldberg E. Chromosomal evolution of Neotropical cichlids: the role of repetitive DNA sequences in the organization and structure of karyotype. Rev Fish Biol Fisher. 2013; 23(2):201-14.), and Australoheros angiru (Heroini) (Paiz et al., 2014Paiz LM, Baumgartner L, Moresco RM, Treco FR, da Graça WJ, Margarido VP. Evolutionary and biogeographical approach on Australoheros angiru (Cichlidae) from lagoons in a dividing plateau between the basins of the Iguassu River and the Uruguay River, Brazil. Rev Fish Biol Fisher. 2014; 24(1):399-407.). However, these cistrons are found in different locations in other species. In G. brasiliensis (Perazzo et al., 2013Perazzo GX, Noleto RB, Vicari MR, Gava A, Cestari MM. Trends of karyotypical evolution in the pearl cichlid, Geophagus brasiliensis, from southern Brazil. Zoology. 2013; 116(5):286-92.) and Bujurquina peregrinabunda (Cichlini) (Schneider et al., 2013Schneider CH, Gross MC, Terencio ML, Artoni RF, Vicari MR, Martins C, Feldberg E. Chromosomal evolution of Neotropical cichlids: the role of repetitive DNA sequences in the organization and structure of karyotype. Rev Fish Biol Fisher. 2013; 23(2):201-14.), for example, they are found in a terminal position on the long arm of the subtelo-acrocentric chromosomes. In Hoplarchus psittacus (Heroini), they are found in a terminal position on the short arm of the subtelo-acrocentric chromosomes, while in Symphysodon discus (Heroini), they are in a terminal position on the short arm of the meta-submetacentric chromosomes (Schneider et al., 2013Schneider CH, Gross MC, Terencio ML, Artoni RF, Vicari MR, Martins C, Feldberg E. Chromosomal evolution of Neotropical cichlids: the role of repetitive DNA sequences in the organization and structure of karyotype. Rev Fish Biol Fisher. 2013; 23(2):201-14.). Multiple 5S rDNA cistrons are uncommon in cichlines, although they have been observed in Crenicichla lepidota (Geophagini), on four chromosomes (Perazzo et al., 2011Perazzo GX, Noleto RB, Vicari MR, Gava A, Cestari MM. Trends of karyotypical evolution in the pearl cichlid, Geophagus brasiliensis, from southern Brazil. Zoology. 2013; 116(5):286-92.), and in Aequidens tetramerus (Cichlasomatini), also on four chromosomes (Nakajima et al., 2012Nakajima RT, Cabral-de-Mello DC, Valente GT, Venere PC, Martins C. Evolutionary dynamics of rRNA gene clusters in cichlid fish. BMC Evol Biol. 2012; 12:198-222.), located in an interstitial position on the long arm of the subtelo-acrocentric chromosomes. In Caquetaia spectabilis (Heroini), the cistrons were also found on four chromosomes, located in an interstitial position on the long arm and in a terminal position on the short arm of the subtelo-acrocentric chromosomes (Schneider et al., 2013Schneider CH, Gross MC, Terencio ML, Artoni RF, Vicari MR, Martins C, Feldberg E. Chromosomal evolution of Neotropical cichlids: the role of repetitive DNA sequences in the organization and structure of karyotype. Rev Fish Biol Fisher. 2013; 23(2):201-14.). Overall, then, simple 5S rDNA cistrons located in interstitial position on the long arm of the subtelo-acrocentric chromosomes, as observed in G. setequedas (Fig. 2c), represent a plesiomorphic character (Fig. 3).

The presence of heterochromatin in the centromeric and pericentromeric regions of most of the chromosomes of the complement has also been observed in Gymnogeophagus gymnogenys, Geophagus brasiliensis (Pires et al., 2010Pires LB, Giuliano-Caetano L, Dias AL. Cytogenetic characterization of Geophagus brasiliensis and two species of Gymnogeophagus (Cichlidae: Geophaginae) from Guaíba Lake, RS, Brazil. Folia Biol. 2010; 58(1-2):29-34.), Biotodoma cupido and Geophagus proximus (Valente et al., 2012Valente GT, Vitorino CA, Cabral-de-Mello DC, Oliveira C, Souza IL, Martins C, Venere PC. Comparative cytogenetics of ten species of cichlid fishes (Teleostei, Cichlidae) from the Araguaia River system, Brazil, by conventional cytogenetic methods. Comp Cytogenet. 2012; 6(2):163-81.) (Geophagini), Cichla monoculus (Schneider et al., 2013Schneider CH, Gross MC, Terencio ML, Artoni RF, Vicari MR, Martins C, Feldberg E. Chromosomal evolution of Neotropical cichlids: the role of repetitive DNA sequences in the organization and structure of karyotype. Rev Fish Biol Fisher. 2013; 23(2):201-14.) (Cichlini), Cichlasoma facetum (probably Australoheros tavaresi Ottoni, 2012) (Vicari et al., 2006Vicari MR, Artoni RF, Moreira-Filho O, Bertollo LAC. Basic and molecular cytogenetics in freshwater Cichlidae (Osteichthyes, Perciformes) Karyotypic conservationism and divergence. Caryologia. 2006; 59(3):260-66.), and the heroin, A. angiru (Paiz et al., 2014Paiz LM, Baumgartner L, Moresco RM, Treco FR, da Graça WJ, Margarido VP. Evolutionary and biogeographical approach on Australoheros angiru (Cichlidae) from lagoons in a dividing plateau between the basins of the Iguassu River and the Uruguay River, Brazil. Rev Fish Biol Fisher. 2014; 24(1):399-407.) (Heroini). This is a common pattern in Neotropical cichlids (Feldberg et al., 2003Feldberg E, Porto JIR, Bertollo LAC. Chromosomal changes and adaptation of cichlid fishes during evolution. In: Val AL, Kapoor BG, editors. Fish adaptation. Enfield: Science Publishers Inc; 2003. p.285-308.; Valente et al., 2012Valente GT, Vitorino CA, Cabral-de-Mello DC, Oliveira C, Souza IL, Martins C, Venere PC. Comparative cytogenetics of ten species of cichlid fishes (Teleostei, Cichlidae) from the Araguaia River system, Brazil, by conventional cytogenetic methods. Comp Cytogenet. 2012; 6(2):163-81.). However, while this is a conserved pattern, some variation has been observed, indicating the occurrence of rearrangements during the chromosomal evolution of some groups (Feldberg et al., 2003Feldberg E, Porto JIR, Bertollo LAC. Chromosomal changes and adaptation of cichlid fishes during evolution. In: Val AL, Kapoor BG, editors. Fish adaptation. Enfield: Science Publishers Inc; 2003. p.285-308.; Roncati et al., 2007Roncati HA, Pastori MC, Fenocchio AS. Cytogenetic studies and evolutive considerations on fishes of the family Cichlidae (Perciformes) from Parana River (Argentina). Cytologia. 2007; 72(4):379-84.; Perazzo et al., 2013Perazzo GX, Noleto RB, Vicari MR, Gava A, Cestari MM. Trends of karyotypical evolution in the pearl cichlid, Geophagus brasiliensis, from southern Brazil. Zoology. 2013; 116(5):286-92.).

Remarks on the conservation status ofG. setequedas. Since its discovery, the conservation status of Gymnogeophagus setequedas has invariably been assigned to a threatened category. The threat has been attributed to lentic waters of the Itaipu Reservoir, which have isolated populations of this rheophilic species, which formerly occurred on tributaries of both banks, in Paraguay and Brazil, and probably in the lower Paraná River proper. After the construction of the reservoir, these populations disappeared. The recent new records of G. setequedas in the Iguaçu River extend the geographical distribution of the species from its original description.

Prior to their formal publication herein, these data were also considered in the most recent evaluation of the conservation status of the Brazilian populations, which led to reclassification of G. setequedas as endangered in accordance with IUCN (2014International Union for Conservation of Nature (IUCN). Standards and Petitions Subcommittee. Guidelines for using the IUCN Red List Categories and Criteria. Version 11 [Internet]. 2014. Available from: http://www.iucnredlist.org/documents/RedListGuidelines.pdf
http://www.iucnredlist.org/documents/Red...
) criterion B. Its previously known distribution in the Iguaçu River spanned about 100 km from above the Iguaçu Falls to the middle of the Itaipu Reservoir. That value yields an estimated extent of occurrence (EOO) of just 200 km2 by multiplying the linear extent of the river where the species occurs by two, according to the IUCN recommendation for the rough calculation of the area of a drainage basin (personal communication with M. F. Tognelli, Program Officer, IUCN | CI Biodiversity Assessment Unit, Global Species Programme, in 2012, when the species was reassessed). The inclusion of the newly discovered lot from Porto Vorá would add a river extension of 225 km2. Multiplying 225 km2 by two would result in an addition of 450 km2 to the extent of occurrence (EOO) of the species, totaling 650 km2, which is still far below the IUCN threshold of 5,000 km2 for classifying the species as endangered. The reservoir’s severe fragmentation of the population and the continued decline in original extent of occurrence (EOO), area of occupancy (AOO), and area, extent and quality of habitat caused by deforestation, silting and pollution by pesticides, consequences of agriculture and livestock satisfy subcriteria B.1.a(i,ii,iii) and B.1.b(i,ii,iii).

The fact that the known healthy populations of this species occurs only in stretches of the Iguaçu River free of impoundment reinforces the requirement of rapid waters for its survival. Its sporadic capture only twice after building reservoirs, such as Itaipu and Salto Caxias, and its later disappearance detected by monitoring those two large reservoirs confirm its dependence on rapid environments. As the construction of a new hydroelectric power station (Baixo Iguaçu) is already under way between the Caxias Reservoir and the Iguaçu Falls, we strongly recommend keeping the tributaries and the area downstream from the reservoir free of additional dams, to guarantee the long-term survival of the species.

Acknowledgments

We are grateful to Instituto Chico Mendes de Conservação da Biodiversidade (ICMBio) for authorizing capture of the fishes (License number: SISBIO 10522-1). We also thank the Universidade Estadual do Oeste do Paraná (UNIOESTE), Parque Nacional do Iguaçu, Macuco Safari and Núcleo de Pesquisas em Limnologia, Ictiologia e Aquicultura (Nupélia) for logistical support. Coordenadoria de Aperfeiçoamento de Ensino Superior (CAPES), Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) and Fundação Parque Tecnológico Itaipu (FPTI-BR) financed this study. Thanks are given to Carlos Lucena (MCP), whose project: Qualificação taxonômica da base de dados da coleção de peixes do Museu de Ciências e Tecnologia - PUCRS para uso online (MCT/CNPq, no45/2012 process: 504177/2012-5), provided grants to WJG to analyze specimens of Cichlidae housed in the MCP ichthyology collection. WJG was partially supported by a research grant from the Fundação Araucária (Secretaria da Ciência, Tecnologia e Ensino Superior do Paraná, covenant #471/2013, protocol #36204), and CSP by a research grant from the Conselho Nacional de Desenvolvimento Científico e Tecnológico (process #308946/2012-0).

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Publication Dates

  • Publication in this collection
    2017

History

  • Received
    03 May 2016
  • Accepted
    06 June 2017
Sociedade Brasileira de Ictiologia Universidade Estadual de Maringá, Núcleo de Pesquisas em Limnologia, Ictiologia e Aquicultura/Coleção Ictiologia, Av. Colombo, 5790, 87020-900 Maringá, PR, Brasil, Tel.: (55 44)3011 4632 - Maringá - PR - Brazil
E-mail: neoichth@nupelia.uem.br