Karyotype similarity between two sympatric Schizodon fish species (Anostomidae, Characiformes) from the Paraguay River basin

Abstract

Fish of the neotropical family Anostomidae generally show low karyotype variability. Nevertheless, karyotype variants have been identified within some genera, providing information about their evolutionary history. Species of the genus Schizodon show a high degree of morphological and ecological similarity compared to other anostomids. In the present study, karyotype characteristics of Schizodon borelli (40 individuals) and S. isognathum (one individual), two sympatric species found in the Paraguay River basin, were studied. C-banding, GC-specific fluorochrome Mitramycin (MM) and Ag staining as well as in situ hybridization (FISH) with rDNA probes were used. The karyotypes of these species were found to be very similar. Only two NORs were detected in a common chromosome pair of both species under Ag, MM and FISH treatments. Similar heterochromatin distribution patterns were also observed. A parallelism between the small karyotype variation and low morphological and ecological divergence observed for this genus is discussed. Their karyotype homogeneity might be related to populational features or, alternatively, might indicate that the maintenance of a symmetric and conserved karyotype structure represents optimal genomic organization among these fish.<br>Peixes neotropicais da família Anostomidae apresentam, de uma forma geral, pouca variação na sua estrutura cariotípica. Mesmo assim, em alguns grupos, foi possível identificar variantes cariotípicas que forneceram informações tanto sobre sua sistemática quanto sobre sua história evolutiva. As espécies do gênero Schizodon apresentam um alto grau de similaridades ecológicas e morfológicas comparado com outros anostomídeos. No presente trabalho, foram estudadas características cariotípicas de S. borelli (40 indivíduos analisados) e S. isognathum (somente um indivíduo analisado), duas espécies simpátricas do rio Paraguai, utilizando bandamento C, coloração com nitrato de prata, aplicação do fluorocromo GC-específico mitramicina e hibridação in situ (FISH) com sonda de DNAr. Os cariótipos destas espécies mostraram-se muito similares. Somente duas NORs foram detectadas sob os tratamentos com Ag, MM e FISH em um par cromossômico comum a ambas as espécies e um padrão similar de distribuição da heterocromatina também foi observado. Estes dados sugerem a existência de um paralelismo entre a pouca variação cromossômica e a baixa divergência ecológica e morfológica observada neste gênero. A homogeneidade cariotípica observada pode estar relacionada a fatores populacionais ou pode indicar que a manutenção de uma estrutura cariotípica conservada e simétrica representa a melhor forma para a organização do genoma destes peixes

Evolutionary cytogenetics of the Hoplias lacerdae, Miranda Ribeiro, 1908 group: a particular pathway concerning the other Erythrinidae fish

“…However, ribosomal cistrons were not detected in these four chromosomes after FISH. Similar cases in which GC-rich sites were not correlated with NORs have also been observed in few other fish, such as in species of the genus Schizodon (Martins and Galetti Jr., 1998), Liposarcus and Leporinus (Artoni et al, 1999), Eigenmannia (Almeida-Toledo et al, 2000), and some Loricariidae (Kavalco et al, 2004). According to Sumner (1990), chromosome staining with silver nitrate may also highlight argentophilic heterochromatic sites, which can explain the present results.…”

Nuclear DNA content determination in Characiformes fish (Teleostei, Ostariophysi) from the Neotropical region

“…from the Acre river (Table I). This difference of about 1.11 pg cannot be related to the karyotypic macrostructure of the species in that all the species studied that belong to these two genus exhibit 2n = 54 chromosomes and metacentric and submetacentric chromosomes (Galetti Junior et al, 1991;Galetti Junior et al, 1995;Martins and Galetti Junior, 1998).…”

Nucleolar organizer regions as markers of chromosomal polymorphism in Apareiodon affinis (Pisces, Parodontidae)

“…This hypothesis is reinforced by the absence of acrocentric chromosomes in most of Parodon and Apareiodon species (Moreira- Filho et al 1980Filho et al , 1984Filho et al , 1985Filho et al , 1993Jesus 1996; Jesus and Moreira -Filho 2000 a, b), excepting A. affinis from Cuiabá River (Jesus et al 1999). Besides that, other families related to Parodontidae (Prochilodontidae, Curimatidae, Anostomidae, Chilodontidae) present 2n=54 and NF=108, with M/SM chromosomes (Galetti Jr. et al 1981 a, b;Pauls andBertollo 1983, 1990;Feldberg et al 1987;Feldberg et al 1992;Venere and Galetti Jr. 1989;Martins andGaletti Jr. 1997, 1998).…”

“…The interstitial position of these genes was also observed in other fish groups such as Anguilla anguilla , Coregonus arditi and C. zenithicus (Sajdak et al 1998), Leporinus spp. (Martins and Galetti Jr. 1999), and Hoplias malabaricus (BORN and Bertollo 2000). The presence of interstitial 5S ribosomal genes on both arms of the subtelocentric chromosome can be related to pericentric inversion of an original metacentric chromosome, suggesting a polymorphism for this region and constituting, as well as NORs, a marker for the rearrangements occurred in this species.…”

“…The amplification products were kindly provided by Dr. HATANAKA (UFSCar). The 5S rDNA probe was composed by the recombinant plasmid p-BS/KS containing the 5S rRNA gene from Leporinus elongatus (Martins and Galetti Jr. 1999). The fragments of 5S (about 200 bp) and 18S (about 1800 bp) rDNA were purified with Kit Sephaglass Band Prep (Pharmacia Biotech).…”