Comparative cytogenetics of six Indo‐Pacific moray eels (Anguilliformes: Muraenidae) by chromosomal banding and fluorescence in situ hybridization

Abstract

A comparative cytogenetic analysis, using both conventional staining techniques and fluorescence in situ hybridization, of six Indo-Pacific moray eels from three different genera (Gymnothorax fimbriatus, Gymnothorax flavimarginatus, Gymnothorax javanicus, Gymnothorax undulatus, Echidna nebulosa and Gymnomuraena zebra), was carried out to investigate the chromosomal differentiation in the family Muraenidae. Four species displayed a diploid chromosome number 2n = 42, which is common among the Muraenidae. Two other species, G. javanicus and G. flavimarginatus, were characterized by different chromosome numbers (2n = 40 and 2n = 36). For most species, a large amount of constitutive heterochromatin was detected in the chromosomes, with species-specific C-banding patterns that enabled pairing of the homologous chromosomes. In all species, the major ribosomal genes were localized in the guanine-cytosine-rich region of one chromosome pair, but in different chromosomal locations. The (TTAGGG)n telomeric sequences were mapped onto chromosomal ends in all muraenid species studied. The comparison of the results derived from this study with those available in the literature confirms a substantial conservation of the diploid chromosome number in the Muraenidae and supports the hypothesis that rearrangements have occurred that have diversified their karyotypes. Furthermore, the finding of two species with different diploid chromosome numbers suggests that additional chromosomal rearrangements, such as Robertsonian fusions, have occurred in the karyotype evolution of the Muraenidae.

Chromosome Mapping of 5S Ribosomal Genes in Indo-Pacific and Atlantic Muraenidae: Comparative Analysis by Dual Colour Fluorescence In Situ Hybridisation

“…The chromosomes were classified according to Levan et al (1964) [33]. Idiograms of the species were constructed on the basis of the relative length and centromeric index of each chromosome pair obtained from the analysis of at least 15 Wright's stained and C-banded karyotypes, as previously described [23,25,27,32].…”

“…The Murenidae is the most species-rich and studied family among the Muraenoidea. Cytogenetically, the moray species show a quite conserved chromosome number of 42; only 4 out of 21 species are characterised by different chromosome numbers: G. kidako (2n = 36) [21], G. moringa (2n = 44) [22], G. javanicus (2n = 40), and G. flavimarginatus (2n = 36) [23]. Despite chromosome number conservation, strong cytogenetic diversity is present among morays, with karyotypes ranging from mainly bi-brachial in G. miliaris to all mono-brachial in G. pictus, and with a prevalence of karyotypes showing many subtelo-acrocentric chromosomes (see the table I in Coluccia et al [23]).…”

“…However, cytogenetic data are still scarce for the whole Muraenidae family. Only 21 species have been studied, and these studies have been restricted mainly to heterochromatin and nucleolar organizer region localisation by silver staining (AgNORs); furthermore, the mapping of major rDNA and telomeric sequences using fluorescence in situ hybridisation (FISH) was achieved in nine species (see the Table I in Coluccia et al [23]) [22]. Only three species (Muraena helena, G. unicolor, and G. tile) were analysed and compared by replication banding, and the conservation of many chromosome pairs among these three species has been reported [24,25].…”

“…The chromosomal localisation of 5S rDNA sites was compared with the major ribosomal gene sites previously localised [23,25,26,28]. In some species, the two ribosomal gene families were detected nearby positions on the same chromosome; therefore, dual colour FISH experiments using both ribosomal probes were conducted to detect possible association on the same pair.…”

Mitogenome of Gymnothorax minor and Phylogenetic Relationship with Its Congeners and Related Genera (Anguilliformes: Muraenidae)

“…Members of the genus range in total length from 6.5 cm (G. parini) to 300 cm (G. favagineus and G. javanicus) (www.fishbase.org). Most of the species (13/16) studied to date possess a diploid number of 2n = 42 chromosomes, excepting 2n = 40 for G. javanicus and 2n = 36 for G. flavimarginatus and G. kidako (Coluccia et al 2015).…”