Cytogenetics of Synbranchiformes: a comparative analysis of two Synbranchus Bloch, 1795 species from the Amazon

Abstract

Synbranchidae belongs to the Synbranchiformes and occurs in Africa, Asia, Australia, Mexico, and Central and South America. This family comprises four genera: Synbranchus, Ophisternon, Monopterus, and Macrotrema. Only two are known from the neotropical region, Ophisternon and Synbranchus. According to current classification, Synbranchus has three valid species: S. marmoratus (Bloch 1795), S. madeirae (Rosen and Rumney 1972), and S. lampreia (Favorito, Zanata and Assumpção 2005). Thus the present research is aimed to cytogenetically characterize (by classical and molecular methods) two syntopic species-S. aff. lampreia and S. madeirae-from the central Amazon basin to validate the taxonomy of both species and provide a revisionary discussion on the cytogenetics of Synbranchiformes. Synbranchus aff. lampreia was found to possess 2n = 44 chromosomes (6 m + 2st + 36a, NF = 50), while S. madeirae had 2n = 46 chromosomes (6 m + 2st + 38a, NF = 52). Constitutive heterochromatin was dominant in the centromeric and terminal regions of most of the chromosomes in both species, although the precise distribution patterns were species-specific. The nucleolar organizing region was single in S. aff. lampreia and multiple in S. madeirae, as indicated by both AgNO(3) and hybridization using 18S rDNA probes. The 5S rDNA sites were located interstitially on the long arms of an acrocentric pair in both species, and the telomeric probe did not show any interstitial sites in either species. These data indicate the occurrence of interspecific karyotypic variability in Synbranchus and suggest that taxonomic review for this genus is necessary.

Twenty Years of Physical Mapping of Major Ribosomal RNA Genes across the Teleosts: A Review of Research

“…In protacanthopterygians, multiple NORs appear in salmons, as in Salmo trutta [Caputo et al, 2009] and Salvelinus fontinalis [Fujiwara et al, 1998], the species that show the highest number of rDNA sites so far reported, as well as in 2 umbrid species (Esociformes) [Ráb et al, 2002]. On the other hand, multiple rDNA sites are more an exception than a rule within the acanthopterygian species studied so far, such as Aphanius fasciatus (Cyprinodontiformes) [Vitturi et al, 2005], Nerophis ophidion and Syngnathus abaster (Syngnathiformes) [Libertini et al, 2006], Monopterus albus and Synbranchus madeira (Synbranchiformes) [Ji et al, 2003;Carvalho et al, 2012]. In Perciformes, a highly conserved single-site pattern is noticeably altered only within the suborder Labroidei, especially in cichlid subfamilies Cichlasomatinae and Pseudocrenilabrinae [Gross et al, 2010;Poletto et al, 2010b], and sporadically in other taxa, as in 1 species of Labridae, Coris julis [Mandrioli et al, 2000a], in 1 species of Sparidae, Diplodis sargus [Merlo et al, 2013], and in 2 notothenioid species Ghigliotti et al, 2007].…”

Molecular and cytogenetic analyses of cryptic species within the Synbranchus marmoratus Bloch, 1795 (Synbranchiformes: Synbranchidae) grouping: species delimitations, karyotypic evolution and intraspecific diversification

“…Herein, an extensive intrapopulational polymorphism of 18S rDNA sites in several karyomorphs was detected and seems to be related to the association of these sequences with transposable elements or with their telomeric position, which would facilitate the transference of this material during interphase (Foresti et al, 1981;Mantovani et al, 2005). Furthermore, these polymorphic differences have also been detected in other Synbranchus species (Carvalho et al, 2012), suggesting that this is a common characteristic in this group of organisms. Thus, 18S rDNA dispersion was likely already present before the diversification of these species/karyomorphs.…”

“…However, many morphological traits can be subtle or ambiguous, which often makes it difficult to recognize and describe new species. Therefore, it is necessary to increase the number of tools and characteristics available for differentiating species from this group (Nakamoto et al, 1986;Foresti et al, 1992;Melilo et al, 1996;Sanchez & Fenocchio, 1996;Perdices et al, 2005;Torres et al, 2005;Nirchio et al, 2011;Carvalho et al, 2012). In the present study, several karyomorphs of S. marmoratus collected in distinct Brazilian river basins were described.…”

“…Variations related to NORs have already been detected in Synbranchus and indicate that microstructural rearrangements occur frequently and contribute to the karyotypic differentiation of these fish (Foresti et al, 1992;Melillo et al, 1996;Sanchez & Fenocchio, 1996;Carvalho et al, 2012). Herein, an extensive intrapopulational polymorphism of 18S rDNA sites in several karyomorphs was detected and seems to be related to the association of these sequences with transposable elements or with their telomeric position, which would facilitate the transference of this material during interphase (Foresti et al, 1981;Mantovani et al, 2005).…”

“…The occurrence of species with distinct diploid numbers in Synbranchidae reveals that fusion/fission rearrangements are fundamental mechanisms in the karyoevolution of this group (Torres et al, 2005;Carvalho et al, 2012). Hypotheses concerning the primitive diploid number in Synbranchus have already been proposed, but lead to opposite predictions (Melilo et al, 1996;Torres et al, 2005).…”