Karyotypic characterization of the bat species Molossus ater, M. molossus and Molossops planirostris (Chiroptera, Molossidae) using FISH and banding techniques.

The karyotypes of the bat species Molossus ater, M. molossus (2n = 48; NF = 64) and Molossops planirostris (2n = 34; NF = 60) were analyzed by G-, C-banding, silver nitrate staining (AgNO3), base-specific fluorochromes and fluorescent in situ hybridization (FISH). The two species of Molossus presented the constitutive heterochromatin (CH) in the pericentromeric regions of all autosomes and in the X chromosome, while the Y chromosome was completely heterochromatic. Molossops planirostris showed conspicuous CH blocks in the pericentromeric regions of the pairs 4, 5, 8, 15, 16 and in the short arm of the X chromosome, while the Y did not present any CH block. Pretreated slides for C-banding stained with DAPI (CB-DAPI) revealed a similar pattern of C-banding (CBG) for these species. Sequential staining (AgNO3/CMA3/DAPI) in M. planirostris showed that the nucleolus organizer regions (NORs) are weakly CMA3 positive and DAPI negative. In the three species, triple staining with CMA3/DA/DAPI revealed R-banding with CMA3 and uniform staining with DAPI. The ribosomal cistrons detected by FISH were present only in the pair 5 in both species of Molossus, and in two pairs of medium sized chromosomes (pairs 9 and 10) of Molossops planirostris. The results obtained by FISH, compared with those by AgNO3 staining, indicated that all NORs in these species are transcriptionally active.