New highly discordant chromosome number and cytogenetic characterization in Trigona (Apidae, Meliponini)

Trigona comprises 35 species, of which 25 occur in Brazil. Of these, 12 species have been cytogenetically investigated and most showed the chromosome number 2n = 34, except for Trigona braueri, which showed 2n = 32, due to a probable numerical reduction by chromosome fusion. In this study, Trigona pellucida was cytogenetically analyzed by classical and molecular techniques (Giemsa staining, CMA₃/DAPI fluorochrome staining and FISH using 18S rDNA, telomeric and microsatellite probes). New chromosome numbers, n = 10 and 2n = 20 and the diploid karyotypic formula 2 k = 14 M + 4SM + 2A were described. These new chromosome numbers were quite divergent from the other Trigona and such intrageneric variation was unexpected in the tribe Meliponini. CMA₃/DAPI fluorochromes staining showed CMA₃ positive segments in all chromosomes of T. pellucida, which was also divergent from other Trigona species. In situ hybridization with 18S rDNA probes occurred on the short arm of both chromosomes of the ninth pair, which also coincided with CMA₃⁺ regions. Microsatellite probes showed markings on all chromosomes, and in seven pairs these markings occurred in the terminal regions of both arms. FISH with telomeric probes showed regular markings in the terminal regions of the chromosomes. The present result with Trigona pellucida was surprising, and pose more challenges for understanding the karyotypic evolution of stingless bees than previously assumed.