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.

The standardized karyotype and idiogram of the Bengal monitor lizard (Varanus bengalensis) from the Kalasin Province of Thailand were studied. Blood samples were taken from male and female lizards. The standard T-lymphocyte cell was cultured at 26 C for 96 h. The mitotic chromosomes were harvested by colchicine-hypotonic-fixation-air drying technique. Conventional staining, Ag-NOR banding and C-banding techniques were applied to stain the chromosome with 20% Giemsa s solution. The results showed that the number of diploid chromosome was 2n= 40, while the fundamental number (NF) was 54 in males and 55 in females. The types of macrochromosomes were 4 large metacentric, 4 small metacentric, 6 small submetacentric, 2 small telocentric macrochromosomes and 24 microchromosomes. The Z chromosome is the small telocentric chromosome, while the W chromosome is the small metacentric chromosome. In addition, the short arm pericentromeric region of chromosome pair 1 showed clearly observable nucleolar organizer regions (NORs). This data is the first report on polymorphism of NORs in V. bengalensis. The result showed that the heteromorphic of one male had a different size of NORs of chromosome pair 1 (1a1b), while one female had an equal size of both chromosome pair 1 with a homomorphic (1a1a). The karyotype formula is as follows: m m sm t 4 4 6 2 2 (40) =L +S +S +S +Z(t)W(m)+22 microchromosomes n

The cytogenetics of the ornamented pygmy frog (Microhyla fissipes), painted chorus frog (M. pulchra) and narrow-mouthed frog (M. heymonsi) were studied in the aspect of chromosome numbers, morphology and nucleolus organizer region (NOR) locations. For this present study, we provided the karyotype and idiogram of these three species by conventional and Ag-NOR staining techniques. The 10 male and female samples of those three species were collected in Northeast Thailand. The metaphase chromosome preparations were prepared from the bone marrows by the standard protocol. To stain the chromosomes, 10% Giemsa s and 50% silver nitrate were applied. The results showed that all three species had the same diploid chromosome number of 2n=24, and fundamental numbers (NF) were 48 in both males and females. The chromosomes of M. fissipes were comprised of 16m+6sm+XY (X and Y were metacentric chromosomes). M. pulchra had chromosomes consisting of 12m+12sm and M. heymonsi had chromosomes comprising of 18m+6 with no obvious difference in size of sex chromosomes for the two species. M. fissipes and M. pulchra had the same NORs adjacent to the subcentromeric on the long arm of chromosome pair 9, while M. heymonsi had the NOR location on the short arm of chromosome pair 2 close to the centromere. For this case, we suggested that chromosome morphology and the NOR location is still a useful cytological character for taxonomic and evolutionary studies.

Studies of chromosomes of Cyrtodactylus jarujini Ulber, 1993 and C. doisuthep Kunya et al., 2014 to compare microsatellite and TTAGGG sequences by classical and molecular techniques were conducted in Thailand. Karyological typing from a conventional staining technique of C. jarujini and C. doisuthep showed diploid chromosome numbers of 40 and 34 while the Fundamental Numbers (NF) were 56 in both species. In addition, we created the chromosome formula of the chromosomes of C. jarujini showing that 2n (40) = Lsm1 + Lsm2 + Lt3 + Mm1 + Mt4 + Sm2 + Sa2 + St5 while that of C. doisuthep was 2n (34) = Lsm3 + Lm2 + Lt3 + Mm1 + Mt2 + Sm4 + Sa1 + St1. Ag-NOR staining revealed NOR-bearing chromosomes in chromosome pairs 13 and 14 in C. jarujini, and in chromosome pairs 9 and 13 in C. doisuthep. This molecular study used the FISH technique, as well as microsatellite probes including (A)20, (TA)15, (CGG)10, (CGG)10, (GAA)10, (TA)15 and TTAGGG repeats. The signals showed that the different patterns in each chromosome of the Gekkonids depended on probe types. TTAGGG repeats showed high distribution on centromere and telomere regions, while (A)20, (TA)15, (CGG)10, (CGG)10, (GAA)10 and (TA)15 bearing dispersed over the whole genomes including chromosomes and some had strong signals on only a pair of homologous chromosomes. These results suggest that the genetic linkages have been highly differentiated between the two species.

Three species of ornamental fishes in the subfamily Cyprininae (family Cyprinidae) namely, Epalzeorhynchos frenatum (Fowler, 1934), Puntigrus partipentazona (Fowler, 1934), Scaphognathops bandanensis Boonyaratpalin et Srirungroj, 1971 were studied by classical cytogenetic and fluorescent in situ hybridization (FISH) techniques. Chromosomes were directly prepared from kidney tissues and stained by using conventional and Ag-NOR banding techniques. Microsatellite d(CA)15 and d(CGG)10 probes were hybridized to the chromosomes of three cyprinids. The results show that the three cyprinid species share the same diploid number as 2n=50 but there are differences in the fundamental number (NF) and karyotypes i.e. E. frenatum: NF = 78, 18m+10sm+10st+12a; P. partipentazona: NF = 80, 6m+24sm+14st+6a; S. bandanensis: NF = 66, 4m+12sm+34a. NOR positive masks were observed at the regions adjacent to the telomere of the short arm of the chromosome pairs 10 (submetacentric) and 1 (metacentric) in E. frenatum and P. partipentazona, respectively whereas those were revealed at telomeric regions of the long arm of the chromosome pair 9 (acrocentric) in S. bandanensis. The mapping of d(CA)15 and d(CGG)10 microsatellites shown that hybridization signals are abundantly distributed in telomeric regions of several pairs except d(CA)15 repeats in S. bandanensis, which are distributed throughout all chromosomes and d(CGG)10 repeats in P. partipentazona display the high accumulation only in the first chromosome pair.