Cytogenetic study of three microhylid species (Anura, Microhylidae) from Thailand

Abstract

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.