The aim was to broaden knowledge on the cytogenetics of the subtribe Meliponina, by furnishing cytogenetic data as a contribution to the characterization of bees from the genus Oxytrigona. Individuals of the species Oxytrigona cf. flaveola, members of a colony from Tangará da Serra, Mato Grosso State, Brazil, were studied. The chromosome number was 2n = 34, distributed among four chromosomal morphologies, with the karyotype formula 8m+8sm+16st+2t. Size heteromorphism in the first metacentric pair, subsequently confirmed by sequential staining with fluorochrome (DA/DAPI/CMA3), was apparent in all the examined individuals The nucleolar organizing regions (NORs) are possibly located in this metacentric chromosome pair. These data will contribute towards a better understanding of the genus Oxytrigona. Given that species in this group are threatened, the importance of their preservation and conservation can be shown in a sensible, concise fashion through studies such as this.

Este trabalho descreve os cariótipos de oito espécies de abelhas do gênero Melipona, relacionando-os por meio do conteúdo e localização da heterocromatina (técnica de banda C). Todas as espécies estudadas apresentaram 2n = 18 (fêmea) e n = 9 (macho) cromossomos, entretanto encontrou-se uma grande variação no conteúdo de heterocromatina entre seus cariótipos, o que permitiu separá-los em dois grupos funcionais: um reunindo espécies de cariótipo com baixo conteúdo de heterocromatina (M. bicolor bicolor, M. quadrifasciata, M. marginata e M. asilvai) e o outro com cariótipo de alto conteúdo heterocromático (M. seminigra fuscopilosa, M. capixaba, M. scutellaris e M. captiosa). Nas espécies com alto conteúdo de heterocromatina, esta ocupa quase toda a extensão de todos os cromossomos, ficando a eucromatina restrita às extremidades, o que impossibilitou a observação do centrômero. Contrariamente, nas espécies de cariótipos com baixo conteúdo, a heterocromatina foi evidenciada somente em alguns cromossomos. Naqueles em que ela está presente, sua localização foi centromérica ou foi evidenciada no braço curto. A espécie que apresentou menor conteúdo heterocromático foi M. bicolor bicolor, sendo que na fêmea apenas três pares de cromossomos apresentaram heterocromatina. O aumento no conteúdo de heterocromatina pode ser explicado pelo crescimento intersticial e pericentromérico.

We describe the karyotypes of eight bee species of the genus Melipona and compare them in terms of heterochromatin content and location (C-banding technique). All species had 2n = 18 (females) and n = 9 (males) chromosomes, but a wide variation in heterochromatin content was detected among karyotypes. On the basis of these differences, the species were divided into two functional groups, one of them comprising species with a karyotype having a low heterochromatin content (M. bicolor bicolor, M. quadrifasciata, M. marginata, and M. asilvai), and the other species with a high heterochromatin content (M. seminigra fuscopilosa, M. capixaba, M. scutellaris, and M. captiosa). In the species with high heterochromatin content, heterochromatin occupied practically the entire extent of all chromosomes, with euchromatin being limited to the extremities, a fact that prevented observation of the centromere. In contrast, in the species with karyotypes having a low heterochromatin content, heterochromatin was visualized only in some chromosomes. In the chromosomes in which it was present, heterochromatin was located in the centromere or on the short arm. M. bicolor bicolor had the smallest heterochromatin content with only three chromosome pairs presenting heterochromatin in females. Increased heterochromatin content may be explained by interstitial and pericentromeric growth.