Analises citogeneticas em abelhas do genero Melipona (Hymenoptera, Meliponinae)

AUTOR(ES)
DATA DE PUBLICAÇÃO

2002

RESUMO

This work is a contribution to the studies of the cytogenetics of the genus Melipona (Hymenoptera, Meliponini), which were initiated by KERR in 1948. The chromosome number is the same (n=9 e 2n=18) for the 11 species of the genus: Me/ipona marginata, Me/ipona quadrifasciata, Me/ipona bic%r, Melipona compressipes, Me/ipona subnitida, Me/ipona scutellaris, Melipona asi/vae, Melipona seminigra fuscopilosa, Me/ipona capixaba, Melipona crinita, Me/ipona mandacaia. The only species with a different number of chromosomes was Me/ipona quinquefasciata, due to the presence of B chromosomes. These chromosomes varied from 1 to 4 in females and from O to 4 in males. Despite exception, we can consider that the chromosome number is a stable character in the taxon. Some species presented chromosomes with meta, submeta and acrocentric morphologies and the heterochromatin was pericentromeric in the following species: M. marginata, M. quadrifasciata, M. subnitida, M. bic%r, M. asilvae, M. mandacaia and in the A complement of M. quinquefasciata. In M. crinita, M. compressipes, M. scutellaris, M. seminigra fuscopilosa and M. capixaba, the chromosome morphology was difficult to define and the heterochromatin was distributed along most of this the chromosomes, with the euchromatin restricted to the extremities. The B chromosomes of M. quinquefasciata also showed three morphologies. The analysis of minus condensate metaphases showed the presence of different types of B chromosomes: acrocentric, totally heterochromatic and submetacentric, with the shorter arm heterocromatic or euchromatic. The percentage of heterochromatin was calculated for some species: M. bic%r (8%), M. subnitida (17%), M. crinita (54%), M. compressipes (61 %) and M. seminigra fuscopi/osa (73%). In the species in which the heterochromatin is distributed in the whole extension of the chromosomes, the percentage of heterocromatic was always higher than 50%, while in the other species it was less the 50%. Based in the percentage of heterochromatin and chromosomic morphology, the genus was divided in two groups. Group I included the species with a low percentage of the heterochromatin (Iess than 50%) and with pericentromeric distribution. Group 11 included species in which the heterochromatin was distributed in the whole extension of the chromosomes and with percentage more than 50%. C Band, NOR Band, fluorochrome, Restriction Enzymes (RE) and Fluorescent in Situ Hybridization (FISH) were used to differentiate species karyotypes. In species of Group I, sequential coloration with the QM/DA/CMA3/DAPI fluorochromes permitted the identification of heterocromatic and euchromatic bands, most of them rich in AT. In species of Group 11, this technique did not differentiate the chromosomes, but pattern with ER demonstrated the heterochromatin heterogeneity. In M. mandacaia, the treatment with ER permitted to observe in ali the chromosomes, regions with different intensities of coloration, with areas completely cleaved and others resistant. Some regions resistant to ER corresponded to heterochromatin; other resistant areas, even though probably also heterochromatic, were not evidenciated with C bando Thus, the technique of restriction enzymes differed two types of heterochromatin. In M. mandacaia, the treatment with Haelll/Giemsa, permitted to obtain a pattern of longitudinal differentiation in the chromosomes similar to G Band. In M. quinquefasciata, the ER apparently did not cleave the DNA of B chromosomes. In species of Group I, the first pai r of chromosomes presented a heterochromatic heteromorphic block. This pair was Ag-NOR+ in M. asilvae, was cleaved by the restriction enzyme Haelll (GCJ..GC) in M. mandacaia and marked with rDNA probes in M. quinquefasciata, M. quadrifasciata, M. bic%__ro This species of Group 11, M. capixaba and M. compressipes, it was possible to characterize this heterochromatin block with CMA3 and FISH. The heteromorphism of the heterochromatic block corresponded to Nucleolus Organizer Region of the species. In species of Group I, NOR was located in pericentromeric region and in Group 11 in the limit of euchromatin and heterochromatin. Except for M. capixaba, that also showed another localization, in the euchromatic extremity. Based in cytogenetic data of Me/ipona, it is possible to conclude that the genus diverges from models proposed to explain the karyotype evolution in Meliponini and that the change in heterochromatin content among the species involved mechanisms still unknown. The polarity of the heterochromatic content in Melipona was proposed considering Leurotrigona muelleri, as an outgroup. The similarity of content and distribution of heterochromatin of L. muelleri with species of Group I of Melipona was considered primitive, permitting a characterization or Group 11 as a natural group in the genus Me/ipona. B chromosomes in Me/ipona probably originated from an amplification of heterochromatin rich in A T and posterior cleavages, or originated interspecific

ASSUNTO(S)

evolução citogenetica

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