No abstract

Background Synbranchidae or swamp eels are fishes belonging to the order Synbranchiformes that occur in both freshwater and occasionally in brackish. They are worldwide distributed in tropical and subtropical rivers of four different continents. A large degree of chromosomal variation has been found in this family, mainly through the use of conventional cytogenetic investigations. Inside this group, a still almost unexplored species under the cytogenetic point of view is the Asian swamp eel Monopterus albus , a widely distributed species throughout Asia. Here, we tested the hypothesis of chromosomal speciation, where a case of sympatric speciation may occur as the primary consequence of chromosomal rearrangements. We performed a comparative chromosomal analysis of M. albus from 22 different localities in Thailand, using distinct staining methods (C-banding, Ag-NO 3, and Chromomycin A 3 ), and FISH with repetitive DNA probes (5S rDNA, 18S rDNA, Rex1 element and microsatellite repeats). Results This approach evidenced two contrasting karyotypes (named karyomorphs A and B) that varied concerning their 2n and repetitive DNAs distribution, where chromosomal fusions and pericentric inversions were involved in such differentiation. While the karyomorph A has 2n = 24 chromosomes, the karyomorph B has only 2n = 18, both with NF = 24. In addition, karyomorph A contains only acrocentric chromosomes, while karyomorph B contains three unique metacentric pairs. These features highlight that M. albus has already gone through a significant genomic divergence, and may include at least two cryptic species. Conclusions This marked chromosomal differentiation, likely linked to the lifestyle of these fishes, point to the occurrence of a chromosomal speciation scenario, in which fusions and inversions had a prominent role. This highlights the biodiversity of M. albus and justifies its taxonomic revision, since this nominal species may constitute a species complex.

BackgroundIn the present study, conventional and molecular cytogenetic studies were performed in the naked catfish Mystus bocourti (Siluriformes, Bagridae). Besides the conventional Giemsa staining, fluorescence in situ hybridization (FISH) using nine classes of repetitive DNAs namely 5S and 18S rDNAs, U2 snRNA, the microsatellites (CA)15 and (GA)15, telomeric repeats, and the retrotransposable elements Rex1, 3 and 6. was also performed.ResultsM. bocourti had 2n = 56 chromosomes with a karyotype composed by 11 m + 11 sm + 6 st/a and a fundamental number (NF) equal to 100 in both sexes. Heteromorphic sex chromosome cannot be identified. The U2 snRNA, 5S and 18S rDNA were present in only one pair of chromosomes but none of them in a syntenic position. Microsatellites (CA)15 and (GA)15 showed hybridization signals at subtelomeric regions of all chromosomes with a stronger accumulation into one specific chromosomal pair. FISH with the telomeric probe revealed hybridization signals on each telomere of all chromosomes and interstitial telomeric sites (ITS) were not detected. The retrotransposable elements Rex1, 3 and 6 were generally spread throughout the genome.ConclusionsIn general, the repetitive sequences were not randomly distributed in the genome, suggesting a pattern of compartmentalization on the heterochromatic region of the chromosomes. Little is known about the structure and organization of bagrid genomes and the knowledge of the chromosomal distribution of repetitive DNA sequences in M. bocourti represents the first step for achieving an integrated view of their genomes.

Summary Chromosomal characteristics of nucleolar organizer regions/NORs and karyological analysis of the Tokay gecko (Gekko gecko) from Khon Kaen Province, northeast Thailand was studied. Gecko chromosome preparations were conducted by squash technique from bone marrow and testis. Conventional staining and Ag-NOR banding techniques were applied to stain the chromosome with Giemsa s solution. The results showed that the number of diploid chromosomes is 2n=38, while the fundamental number (NF) is 50 in both males and females. The types of chromosomes were 2 large metacentric, 4 large submetacentric, 4 large telocentric, 6 medium telocentric, 4 small metacentric, 2 small acrocentric, and 16 small telocentric chromosomes. NORs are located at the secondary constriction to the telomere on long arm of the largest telocentric chromosome pair 4. There are no sex differences in karyotypes between males and females. We found that during metaphase I the homologous chromosomes showed synapsis, which can be defined as 19 ring bivalents and 19 haploid chromosomes (n=19) at metaphase II as a diploid species. The karyotype formula is as follows:2n (38)

BackgroundThe chromosomal homologies of human (Homo sapiens = HSA) and silvered leaf monkey (Trachypithecus cristatus = TCR) have been previously studied by classical chromosome staining and by fluorescence in situ hybridization (FISH) applying chromosome-specific DNA probes of all human chromosomes in the 1980s and 1990s, respectively.ResultsHowever, as the resolution of these techniques is limited we used multicolor banding (MCB) at an ~250-band level, and other selected human DNA probes to establish a detailed chromosomal map of TCR. Therefore it was possible to precisely determine evolutionary conserved breakpoints, orientation of segments and distribution of specific regions in TCR compared to HSA. Overall, 69 evolutionary conserved breakpoints including chromosomal segments, which failed to be resolved in previous reports, were exactly identified and characterized.ConclusionsThis work also represents the first molecular cytogenetic one characterizing a multiple sex chromosome system with a male karyotype 44,XY1Y2. The obtained results are compared to other available data for old world monkeys and drawbacks in hominoid evolution are discussed.