Karyotypes and chromosomal mapping of some repetitive DNAs in two stingless bee species (Apidae: Meliponini), with the description of a B chromosome in Plebeia genus.

Abstract

Cytogenetic studies on stingless bees have significantly contributed to our understanding of karyotypic evolution and the composition of euchromatin and heterochromatin regions, including repetitive sequences. In this study, we performed classical cytogenetics, chromosomal banding, and mapping of some repetitive sequences in two stingless bee species, Frieseomelitta trichocerata and Plebeia poecilochroa. The species exhibit the typical diploid chromosome number of each genera, 2n=30 for Frieseomelitta and 2n=34 for Plebeia. Additionally, some individuals of P. poecilochroa presented a small heterochromatic B chromosome, showing a numeric variation of n=17 to 18 in males and 2n=34 to 35 in females. In both species heterochromatin is primarily distributed in the short arm and centromeric regions. Centromeric regions were found to be AT-rich in both species, while subterminal/terminal regions of the short arms of one and six chromosomes presented GC-rich sites in P. poecilochroa and F. trichocerata, respectively. The rDNA clusters mapped on two chromosome pairs in F. trichocerata, and in only one in P. poecilochroa. Microsatellites (GA)n, (GAG)n, and (CAA)n were predominantly mapped in euchromatic regions, while the telomeric motif (TTAGG)n mapped to the ends of most chromosomes, including the B chromosome of P. poecilochroa. The other repetitive probes used, including the rDNA clusters, do not label the B chromosome of P. poecilochroa. Our cytogenetic data highlight both similarities and differences when compared to other congeneric species, expanding the chromosomal data for both genera.