New patterns of polymorphism in the karyotypic analysis of the genus Plebeia (Hymenoptera, Apidae)

Plebeia is a taxonomically complex genus of stingless bees characterized by remarkable interspecific morphological similarity. On the other hand, cytogenetic data have been useful to resolve taxonomic uncertainties and to infer the diversification processes. Therefore, the goal of this study was to provide a karyotypic analyses in five nominal taxa of Plebeia from northeastern Brazil: P. droryana Friese (Természetrajzi Füzetek kiadja a Magyar nemzeti Muzeum 23:381–394, 1900), P. cf. mosquito Smith 1863, Plebeia aff. droryana 1, Plebeia aff. droryana 2, and Plebeia aff. fravocincta based on traditional and molecular cytogenetic methods to test their applicability in cytotaxonomy and to understand the karyoevolutionary processes in these bees. All species shared a chromosomal number of 2n = 34, except for some individuals of Plebeia aff. flavocincta that presented up to two small and heterochromatic B chromosomes. Species-specific karyotype formulae were observed while the heterochromatin segments were mainly distributed on short arms and pericentromeric regions of most chromosomes, including subtle C-banding differences in each species. The 18S rDNA sites were terminally located on pair 3 of P. droryana, P. cf. mosquito, Plebeia aff. droryana 2, and Plebeia aff. droryana 1, and on the first metacentric pair in Plebeia aff. flavocincta. These data reinforced the efficiency of cytogenetics as an informative tool to discriminate Plebeia species. The present data suggest that structural rearrangements such as inversions and duplications/deletions of heterochromatin and ribosomal clusters are the main drivers of karyotypic evolution in Plebeia.