Cytogenetic analyses of the stingless bee Partamona helleri collected in the state of Bahia, Northeast Brazil revealed the chromosome numbers n = 18 in the haploid males and 2n = 35 in the diploid females. All karyotypes displayed one large acrocentric B chromosome, which differs from the minute B chromosomes previously described in the populations from southeastern Brazil. Giemsa staining, C-banding and DAPI/CMA 3 fluorochrome staining also revealed a remarkable interpopulational divergence regarding both the regular karyotype and the B chromosomes. The B chromosomes found in the samples from Jequié, Bahia, were entirely heterochromatic, while those found in Cravolândia, Bahia, displayed a euchromatic portion at the telomeric end of the long arm. CMA 3 labeling sites varied from seven to eight between the two localities in Bahia, due to the presence of an extra GC-rich block in the karyotype of the samples from Jequié. This is the first report of a large B chromosome in P. helleri and reveals the occurrence of a geographic differentiation within this species.Key words: stingless Bee, Partamona helleri, geographic variation, supernumerary chromosomes. Partamona is a Neotropical genus of stingless bees with an ample distribution in a wide variety of habitats going from southern Brazil to central Mexico. These habitats include rain forests, cerrado (Brazilian savanna), caatinga, and highlands. Given the existence of morphologically similar species, this group has a problematic taxonomy. Some species can only be recognized by their nesting behavior or nest entrance architecture (Pedro and Camargo, 2003).Of the 33 species currently recognized (Pedro and Camargo, 2003), only eight, P. pearsoni (Tarelho ZVS, 1973, MSc Dissertation, University of São Paulo), P. seridoensis (Brito-Ribon et al., 1999, 2005), P. aiylae, P. vicina, P. mulata, P. nhambiquara (Brito-Ribon et al., 1999), P. peckolti (Brito et al., 2003), and P. helleri (Costa et al., 1992;Brito et al., 1997Brito et al., , 2005, were cytogenetically studied. All these species showed the regular chromosome number 2n = 34, but P. helleri showed a diploid numeric variation ranging from 2n = 34 to 2n = 38, due to the occurrence of up to four minute B chromosomes per individual (Costa et al., 1992;Brito et al., 1997Brito et al., , 2005Tosta et al., 2004). B chromosomes are extra chromosomes to the regular complement and are characterized by their dispensability, independent evolution, and non-Mendelian patterns of inheritance (Beukeboom, 1994). Their origin is a matter of recurrent debate among cytologists. Some have proposed that the appearance of the B chromosomes suggests the involvement of rearrangements in the regular chromosomes, e.g., centric fragment formation through chromosome fusions (Camacho et al., 2000). An alternative hypothesis suggests an origin through interspecific hybridization as observed in the fish Poecilia formosa (Schartl et al., 1995) and in the wasp Nasonia vitripennis (McAllister and Werren, 1997). Brito et al. (1997) distinguis...

ABSTRACT. Scaptotrigona xanthotricha has a wide geographic distribution in the Brazilian Atlantic rainforest. One population from southeast and two from northeast Brazil were analyzed and were found to have chromosome polymorphisms. Although the chromosome number 2n = 34 is conserved in this species, karyotypic analysis revealed clear differences between the three populations. Congruent and ubiquitous multiple nucleolus organizer regions, heterochromatin and CMA 3 -positive blocks were found. The variations suggest that this species is in a process of genetic differentiation. This differentiation process might have been enhanced by restricted nesting preferences, combined with recent extensive fragmentation of the Atlantic rainforest, which limits gene flow between populations.

Cytogenetic studies in Melipona are scarce with only 24 species analyzed cytogenetically. Of these, six species had the rDNA sites physically mapped and characterized by Fluorescent in situ Hybridization (fish). The aim of this study was to perform karyotype analyzes on Melipona species from different regions of Brazil, with a greater sampling representative of the Amazonian fauna and using conventional, fluorochrome staining and FISH with heterologous rDNA probes. The predominant chromosome number was 2n = 18, however, the subspecies M. seminigra abunensis and M. s. pernigra showed 2n = 22 chromosomes. The karyotypes were symmetrical, however M. bicolor, M. quadrifasciata, M. flavolineata, M. fuscopilosa, M. nebulosa presented the first pair heteromorphic in length. CMA3+ blocks also exhibited heteromorphism of size and in almost all cases coincided with rDNA sites, except for M. crinita and M. nebulosa, which presented additional non-coincident CMA3+ blocks. The CMA/ rDNA sites were terminal and interstitial in species with high heterochromatic content, and pericentromeric in those species with low heterochromatic content. In addition to pointing out cytogenetic features of cytotaxonomic importance, the reorganization of the genome in Melipona is discussed.

International audienc

Stingless bees are important pollinators that are severely threatened by anthropic interference, resulting in a strong population decline. Scaptotrigona xanthotricha has a wide distribution in the Atlantic Rainforest, ranging from the northeastern state of Bahia to Santa Catarina in southern Brazil. To understand the genetic structure of S. xanthotricha, 12 species-specific microsatellite loci were analyzed in 42 colonies sampled throughout the species range. The results indicated 5 distinct clusters throughout the sampled area with high rates of genetic diversity, and the greatest diversity was found in southern Bahia. Greater differentiation was observed between samples from the extremes of the distribution, with an F value of 0.189 between cluster 1 and 5. The genetic differentiation analysis for all loci had an F value of 0.113, a result that is consistent with the analysis of molecular variance, which revealed 7.72% of the variation occurring between groups. The Mantel correlation between a genetic differentiation matrix and a geographic distance matrix (r = 0.184, P = 0.043) indicated a tendency toward increased differentiation with increased distance. This study revealed the profile of differentiation and distribution of genetic diversity in this species and indicates parameters that should be considered in future taxonomic revisions and activities for its management and conservation.