Karyotypic description of the stingless bee Melipona quinquefasciata Lepeletier, 1836 (Hymenoptera, Meliponini) with emphasis on the presence of B chromosomes

Stingless bees are distributed widely in the tropics, where they are major pollinators of several plant spe- cies. In this study, the karyotype of Melipona quinquefasciata Lepeletier, 1836 was analysed, with emphasis on the presence of B chromosomes. Post-defecating larvae were analysed using Giemsa staining, the C- banding technique, sequential staining with fluorochromes, and FISH. The chromosome number ranged from 2n = 18 to 22 (females) and from n = 9 to 13 (males) due to the presence of 0–4 B chromosomes. This result demonstrates that M. quinquefasciata has the same chromosomal number as other Melipona Illiger, 1806 species. Considering the A complement, heterochromatin was located only in the pericentro- meric region of pair 1. Staining with chromomycin A 3 (CMA 3 ) and labelling with rDNA probe, indicated that this region corresponded to the nucleolus organising region. The B chromosomes of M. quinquefas- ciata could be found in individuals from different localities, they were completely heterochromatic (C- banding) and uniformly stained by 4’,6-diamidino-2-phenylindole (DAPI). Variations in the number of B chromosomes were detected between cells of the same individual, between individuals of the same colony, and between colonies from different localities

Cytogenetic studies in Trachymyrmex holmgreni Wheeler, 1925 (Formicidae: Myrmicinae) by conventional and molecular methods

Over the past several decades, ant cytogenetic studies have focused on chromosome number and morphology; however, recently, additional information concerning heterochromatin composition and 45S rDNA location has become accessible. The fungus-growing ants are a peculiar ant group that cultivates fungus for food, and Trachymyrmex is suspected to be the sister group of leafcutter ants. Cytogenetic data are so far available for sixn Trachymyrmex species. The present study aimed to increase the knowledge about Trachymyrmex cytogenetics by the chromosomal characterization of Trachymyrmex holmgreni including the karyotyping, fluorochromes staining, 18S rDNA, and microsatellite (GA)15 fluorescence in situ hybridization (FISH). Karyotyped samples from four ant colonies showed 2n = 20 metacentric chromosomes. Centromeric heterochromatin rich in GC base pairs was detected in all chromosomes. FISH revealed the presence of rDNA clusters on the fourth chromosome pair, and an intense spreading of the microsatellite (GA)15 including exclusively euchromatic areas of the chromosomes. The GC-rich heterochromatin observed in different ant species may have a common origin and, thus, phylogenetic implication that needs to be further investigated. To the best of our knowledge, this study is the first report of the use of chromosomal physical location of repetitive DNA sequences by means of microsatellite probes in Formicidae

Estimation of Nuclear Genome Size of Three Species of Camponotus (Mayr, 1861) (Hymenoptera: Formicidae: Formicinae) and Their Cytogenetic Relationship

The chromosome variability among ant species is remarkable, and the processes generating such variation are still under discussion since polyploidy has been observed in some distinct taxa. The chromosome number of species belonging to the Camponotus, subgenera Myrmothrix and Myrmobrachys, are highly different, whereas, the first subgenus has double the number of chromosomes of the second. In order to test the hypothesis of chromosome number doubling through polyploidy, the genome sizes of Camponotus (Myrmothrix) rufipes, Camponotus (Myrmothrix) renggeri and Camponotus (Myrmobrachys) crassus were estimated by flow cytometry. The chromosome number of specimens from the nests studied was also defined. No significant variation was noted in the genome size among them. The mean haploid genome size value (1C) of workers for the three species was 286.16 Mpb (0.29 pg). The polyploidy hypothesis can be ruled out as an evolutionary step linking the karyotype variations among the three studied species since the genome size of C. crassus with 2n = 20 chromosomes was the same as that of C. rufipes and C. renggeri with 2n = 40. The lack of variation in the amount of DNA between the related species C. rufipes and C. renggeri also demonstrate that flow cytometry is not an adequate approach to distinguish them. Our results highlight the importance of combining distinct methods, DNA quantification, and cytogenetics from the same colony. Understanding the path of chromosome evolution of three species with distinct degrees of relatedness should provide further information in enriching our knowledge about the Minimum Interaction Theory

Cytogenetic data on six leafcutter ants of the genus Acromyrmex Mayr, 1865 (Hymenoptera, Formicidae, Myrmicinae): insights into chromosome evolution and taxonomic implications

Cytogenetic data for the genus Acromyrmex Mayr, 1865 are available, to date, for a few species from Brazil and Uruguay, which have uniform chromosome numbers (2n = 38). The recent cytogenetic data of Acromyrmex striatus (Roger, 1863), including its banding patterns, showed a distinct karyotype (2n = 22), similar to earlier studied Atta Fabricius, 1804 species. Karyological data are still scarce for the leafcutter ants and many gaps are still present for a proper understanding of this group. Therefore, this study aimed at increasing cytogenetic knowledge of the genus through the characterization of other six species: Acromyrmex balzani (Emery, 1890), A. coronatus Fabricius, 1804, A. disciger (Mayr, 1887), A. echinatior (Forel, 1899), A. niger (Smith, 1858) and A. rugosus (Smith, 1858), all of which were collected in Minas Gerais – Brazil, except for A. echinatior which was collected in Barro Colorado – Panama. The number and morphology of the chromosomes were studied and the following banding techniques were applied: C-banding, fluorochromes CMA3 and DAPI, as well as the detection of 45S rDNA using FISH technique. All the six species had the same chromosome number observed for already studied species, i.e. 2n = 38. A. balzani had a different karyotype compared with other species mainly due to the first metacentric pair. The heterochromatin distribution also showed interspecific variation. Nevertheless, all the studied species had a pair of bands in the short arm of the first subtelocentric pair. The fluorochrome CMA3 visualized bands in the short arm of the first subtelocentric pair for all the six species, while A. rugosus and A. niger also demonstrated in the other chromosomes. The AT-rich regions with differential staining using DAPI were not observed. 45S ribosomal genes were identified by FISH in the short arm of the first subtelocentric pair in A. coronatus, A. disciger and A. niger. The uniform chromosome number in the genus Acromyrmex (2n = 38) suggests that A. striatus (2n = 22) should be transferred to a new genus. Other aspects of the chromosome evolution in ants are also discussed

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

Cytogenetic characterization of Partamona cupira (Hymenoptera, Apidae) by fluorochromes

Four colonies of the stingless bee Partamona cupira (Hymenoptera: Apidae) were cytogenetically analyzed using conventional staining and the fluorochromes CMA3 e DAPI. The females have 2n = 34 chromosomes (2K = 32 M¯+2 A¯). Some females, however, presented an additional large B acrocentric chromosome, to a total of 2n = 35. Chromosome B and the chromosomal pairs 2, 9 and 10 showed CMA 3+ bands, indicating an excess of CG base-pairs. A clear association was verified between the P. helleri B chromosome SCAR marker and the presence of a B chromosome in P. cupira. The data obtained suggests that B chromosomes in P. helleri and P. cupira share a common origin

Karyotypic description of the stingless bee Oxytrigona cf. flaveola (Hymenoptera, Apidae, Meliponina) of a colony from Tangará da Serra, Mato Grosso State, Brazil

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

Evolutionary dynamics of the karyotype of the wasp Trypoxylon (Trypargilum) nitidum (Hymenoptera, Sphecidae) from the Rio Doce State Park, Minas Gerais, Brazil

Cytogenetic analysis based on the distribution of C-bands showed two groups of karyotypes in a Trypoxylon nitidum population from the Rio Doce Park, State of Minas Gerais, Brazil. One of these groups, that was identical to a previously described karyotype (n = 15; 2n = 30), had a stable chromosome number and was rich in acrocentric chromosomes, whereas the other had a variable chromosome number (n = 12 to 14; 2n = 25 to 28) and was rich in pseudo-acrocentric chromosomes. We propose a hypothesis explaining the dynamics of the modifications which occurred in the karyotype of this species, based on the minimum interaction theory of Imai et al. (1986, 1988, 1994) and on the chromosome rearrangements and heteromorphisms observed by us

Karyotypes and heterochromatin variation (C-bands) in Melipona species (Hymenoptera, Apidae, Meliponinae)

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

C-banding and fluorescent in situ hybridization with rDNA sequences in chromosomes of Cycloneda sanguinea Linnaeus (Coleoptera, Coccinellidae)

The aim of this study was to describe mitotic and meiotic chromosomes of Cycloneda sanguinea using C-banding, flourescent in situ hybridization (FISH) rDNA probes, and sequential FISH/Ag-NOR staining. The chromosome number was 2n = 18 + XX for females and 2n = 18 + Xy for males. The X chromosome was metacentric and the Y chromosome was very small. During meiosis, the karyotypic meioformula was n = 9 + Xyp, and sex chromosomes configured a parachute at metaphase I. At the beginning of pachytene, bivalents were still individualized, and sex chromosomes were associated end-to-end through the heteropycnotic region of the X chromosome. Later in pachytene, further condensation led to the formation of a pseudo-ring by the sex bivalent. All chromosomes showed pericentromeric heterochromatin. FISH and sequential FISH/Ag-NOR staining evidenced the location of the nucleolar organizer region in one pair of autosomes (at spermatogonial metaphase). During meiosis, these genes were mapped to a region outside the sex vesicle by FISH, although Xyp was deeply stained with silver at metaphase I. These results suggest that these argyrophilic substances are of a nucleolar protein nature, and seem to be synthesized by a pair of autosomes and imported during meiosis (prophase I) to the sex pair, during the association of the sex chromosomes. Copyright by the Brazilian Society of Genetics.This research was supported by Fundaçao de Amparo à Pesquisa do Estado de Minas Gerais (APE-MIG), Coordenaçao de Aperfeiçoamento de Pessoal de Ensino Superior (CAPES) and Universidade Federal de Viçosa, Viósa, MG, BrazilPeer Reviewe