Marco Antônio Costa

Occurrence of B chromosomes in Tetragonisca Latreille, 1811 (Hymenoptera, Apidae, Meliponini): a new contribution to the cytotaxonomy of the genus

Tetragonisca angustula and Tetragonisca fiebrigi have recently been listed as valid species. This study aimed to cytogenetically investigate both species, emphasizing the new registry of B chromosomes in the tribe Meliponini. We analyzed colonies of T. angustula and T. fiebrigi collected at Tangará da Serra, Mato Grosso, Brazil, through conventional Giemsa staining, C-banding, and base-specific fluorochrome staining (CMA3/DAPI). T. angustula showed 2n = 34 chromosomes in females and n = 17 in males, with karyotype formula 2K = 34AM. T. fiebrigi showed numeric variation, with chromosome number varying from 2n = 34 to 2n = 36 in females and from n = 17 to n = 18 in males, with karyotype formula 2K = 32AM+2AMc and 2K = 32AM+2AMc + 1 or 2 B-chromosomes. The B chromosomes are heterochromatic. In T. fiebrigi, the CMA3/DAPI staining revealed four chromosomes with a CMA3 positive band. All individuals from the same colony showed the same number of B chromosomes. T. angustula and T. fiebrigi showed karyotype divergence, principally due to the presence of B chromosomes, which are found only in T. fiebrigi. Our data corroborate the status of valid species for both T. angustula and T. fiebrigi, as recently proposed.

Investigation of Partamona helleri (Apidae, Meliponini) B chromosome origin. An approach by microdissection and whole chromosome painting

The stingless bee Partamona helleri in southeast Brazil shows the regular chromosome number 2n = 34 and a variable number of up to four minute B1 or B2 chromosomes. Previous cytogenetic analyses have indicated morphological similarities between the B1 chromosome and chromosome segments in the regular karyotype. In this study, microdissection and chromosome painting were employed along with C banding, NOR banding, and base-specific fluorochrome staining to investigate the origin of the B1 chromosome in P. helleri. B1-generated probe hybridized exclusively to B1 chromosomes. This result suggests an independent origin from the regular karyotype or, alternatively, that the B chromosome may have suffered substantial genetic alterations along its independent evolution. The absence of higher dosages of these small B chromosomes in this population of P. helleri may be related to the existence of either a genetic or cytogenetic constraint in the establishment of such high numbered karyotypes.

New occurrence of B chromosomes in Partamona helleri (Friese, 1900) (Hymenoptera, Meliponini)

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/CMA3 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.

Molecular Phylogeny and Historical Biogeography of the Neotropical Swarm-Founding Social Wasp Genus Synoeca (Hymenoptera: Vespidae)

The Neotropical Region harbors high biodiversity and many studies on mammals, reptiles, amphibians and avifauna have investigated the causes for this pattern. However, there is a paucity of such studies that focus on Neotropical insect groups. Synoeca de Saussure, 1852 is a Neotropical swarm-founding social wasp genus with five described species that is broadly and conspicuously distributed throughout the Neotropics. Here, we infer the phylogenetic relationships, diversification times, and historical biogeography of Synoeca species. We also investigate samples of the disjoint populations of S. septentrionalis that occur in both northwestern parts of South America through Central American and the Brazilian Atlantic rainforests. Our results showed that the interspecific relationships for Synoeca could be described as follows: (S. chalibea + S. virginea) + (S. cyanea + (S. septentrionalis/S. surinama)). Notably, samples of S. septentrionalis and S. surinama collected in the Atlantic Forest were interrelated and may be the result of incomplete lineage sorting and/or mitochondrial introgression among them. Our Bayesian divergence dating analysis revealed recent Plio-Pleistocene diversification in Synoeca. Moreover, our biogeographical analysis suggested an Amazonian origin of Synoeca, with three main dispersal events subsequently occurring during the Plio-Pleistocene.

KARYOTYPE DIFFERENTIATION AMONG FOUR DINOPONERA (FORMICIDAE: PONERINAE) SPECIES

ABSTRACT Ants in the genus Dinoponera (Hymenoptera: Formicidae: Ponerinae) are among the largest sized Formicidae of the World. In Brazil Dinoponera has an allopatric distribution, and several species occur in threatened biomes. We characterized karyotypes of the following 4 species: Dinoponera australis Emery, Dinoponera gigantea Perty, Dinoponera lucida Emery, and Dinoponera quadriceps Santschi. Karyotype analysis found that all 4 species have high numbers of small-sized chromosomes (D. australis, 2n = 114; D. gigantea, 2n = 82; D. lucida, 2n = 118/120; D. quadriceps, 2n = 92). A moderate variation in chromosome number was observed among the 4 species, which suggests the occurrence of chromosome rearrangements during karyotype evolution in Dinoponera. An exclusive AMT chromosome pair was found to occur in all Dinoponera species studied thus far, which we conclude is a probable synapomorphy in Dinoponera.

Isolation and characterization of microsatellites from Scaptotrigona xanthotricha (Apidae, Meliponini): a stingless bee in the Brazilian Atlantic rainforest

Scaptotrigona / population genetics / polymorphism / Hymenoptera Scaptotrigona bees are efficient pollinators as they use odors in marking trails to distant food sources. They build their nests in cavities of large living trees making them susceptible to anthropic actions, such as deforestation. Due to the reduction in population size as a result of fragmentation and destruction of natural habitat, many species are threatened with extinction (Freitas et al. 2009). Scaptotrigona comprises 30 Neotropical species, out of which 18 have been recorded in Brazil (Moure et al. 2007). This genus still harbors many undescribed species and cryptic species complexes (Silveira et al. 2002). Scaptotrigona xanthotricha shows a wide distribution in the Atlantic rainforest ranging from southern to the northeastern Brazil (Silveira et al. 2002). Duarte et al. (2009) reported a remarkable geographical variation in the number and location of the Nucleolus Organizer Regions in this species. This finding lent support to the existence of interpopulational divergence or even additional taxa, thus reinforcing the need for more detailed assessment of this group using molecular markers. Studies on the genetic diversity and population structure of stingless bees have become frequent due to the development of microsatellite markers for several species such as Melipona mondury (Lopes et al. 2010), Melipona bicolor (Peters et al. 1998), and Scaptotrigona postica (Paxton et al. 1999), among others. However, these studies are still scarce when compared to the high diversity within this group. The present study aimed at the identification and characterization of microsatellite loci for S. xanthotricha. An enriched genomic library was constructed from a pool of DNA from 30 individuals of the same colony following Billotte et al. (1999). DNA extraction followed Han and McPheron (1997). Five micrograms of DNA (300 ng/μl) was digested with RsaI and linked to RsaI adapters. The library was enriched for (CT) 8 and (GT) 8 repeats using biotinylated probes attached to streptavidin-labeled magnetic beads as described by the manufacturer (MagneSphere Paramagnetic Particles , Promega). Selected fragments amplified by polymerase chain reaction (PCR) using primers with sequences complementary to the adapters and inserted into the plasmid pGEM-T (Promega) were transformed into competent XL-1 Blue Escherichia coli cells. Once most of the colonies were transformed, 96 were selected for long-term storage at −80°C into a micro-plate. Forty-eight positive clones were sequenced on an automated sequencer ABI PRISM 377 (Applied Biosystems) using SP6 and T7 primers and the Big Dye terminator kit …

Cytogenetic divergence in two sympatric fish species of the genus Astyanax Baird and Girard, 1854 (Characiformes, Characidae) from northeastern Brazil

The fish genus Astyanax is widespread throughout the Neotropical region and is one of the most species-rich genera of the Characiformes. Cytogenetic studies of Astyanax have revealed marked intra- and interspecific diversity, with the identification of various species complexes. In this report, we describe the karyotypic structure of two sympatric species of Astyanax (Astyanax sp. and Astyanax aff. fasciatus) from the Middle Contas River basin in the northeastern Brazilian state of Bahia. Both species had 2n = 48 but differed in their karyotypic formulae. Small heterochromatic blocks and multiple nucleolar organizer regions (NORs) were identified in both species. Terminal CMA3+/DAPI− signals were observed in Astyanax sp. and A. aff. fasciatus, mostly coincident with NORs. These results show that chromosomal markers can be used to identify species in this fish complex. These markers can provide useful information for evolutionary studies and investigations on the mechanisms of chromosomal diversity in Astyanax.

A new cluster-brood building species of Plebeia (Hymenoptera, Apidae) from eastern Brazil

A new cluster-brood building species of Plebeia (Hymenoptera, Apidae) from eastern Brazil. A new species of Plebeia, the second largest genus of stingless bees in the Neotropical region, is described from eastern Brazil. Plebeia grapiuna sp. nov., known only from the lowland forests of southern Bahia, is most similar to P. lucii Moure, a species recently described from Minas Gerais. The lack of yellow marks and the smoother integument of the frons and mesoscutum in P. grapiuna sp. nov. distinguish them. Main features of the nesting habits of the new species are described and illustrated.

The roles of barriers, refugia, and chromosomal clines underlying diversification in Atlantic Forest social wasps

Phylogeographic studies have sought to explain the genetic imprints of historical climatic changes and geographic barriers within the Brazilian Atlantic Forest (AF) biota, and consequently two processes of diversification (refugia and barriers) have been proposed. Additionally, there is evidence that eustatic changes influenced the biogeographic history of the AF. Here we evaluate these contrasting diversification processes using two AF social wasp species – the mid-montane Synoeca cyanea and the lowland Synoeca aff. septentrionalis. We analyzed several sources of data including multilocus DNA sequence, climatic niche models and chromosomal features. We find support for idiosyncratic phylogeographic patterns between these wasps, involving different levels of population structure and genetic diversity, contrary suitable climatic conditions during the last glaciation, and contrasting historical movements along the AF. Our data indicate that neotectonics and refugia played distinct roles in shaping the genetic structure of these wasps. However, we argue that eustatic changes influenced the demographic expansion but not population structure in AF biota. Notably, these wasps exhibited chromosomal clines, involving chromosome number and decreasing of GC content, latitudinally oriented along the AF. Together, these results reinforce the need to consider individual organismal histories and indicate that barriers and refugia are significant factors in understanding AF evolution.

Unprecedented record of ten novel B chromosomes in the stingless bee Partamona helleri (Apidae, Meliponini)

Partamona helleri from southeastern Brazil has shown the presence of up to four minute supernumerary chromosomes of the B1 or B2 type and a numeric variation from 2n = 34 to 38 chromosomes. Since the maximum dosage of four of these Bs per individual has been observed, the existence of genetic mechanisms controlling their accumulation has been suggested. In this study, several new types of B chromosomes were found in other localities of the geographic distribution of this species, especially nearby the northern end of the species range, showing a numeric variation of n = 18 to 19 in males and 2n = 34 to 2n = 41 in females. Ten novel types of acrocentric and metacentric B chromosomes were classified as B3 to B12. Eight types were found in the state of Bahia and two types in the state of Espírito Santo. The results suggest that these Bs have had different evolutionary mechanisms involved in their origin and diversification. A variation within and between geographic samples in the number of chromomycin A3 and Ag-NOR markings was observed as a result of the presence or absence of different Bs. Six different B chromosomes showed Ag-NOR markings, which denote presence of gene activity. The karyotype variation and the patterns of B chromosome distribution observed indicate that this species is likely undergoing a process of genetic differentiation.