Contribuição a citogenetica de Trypoxylon (Trypargilum) albitarse Fabricius, 1804 (Hymenoptera, Sphecidae) : I. Dinamica dos cromossomos B II. Estudos da NOR e nucleolos

AUTOR(ES)
DATA DE PUBLICAÇÃO

2002

RESUMO

Among the 13 cytogenetica1ly analysed species of Trypoxylon genus, only T. albitarse possess B chromosomes. Two types morphologically distinct of B chromosomes have been found in this wasp, one metacentric and other acrocentric, which are totally heterochromatic. Over the last five years (1996 the 2000), 1003 specimens of T. albitarse obtained from 692 nests, had been cytogenetically studied with respect to the occurrence, distribution, frequency and evolution of its B chromosomes. Many of these individuals had been subjected to techniques of fluorescent in situ hybridisation (FISH) or silver nitrate staining for location of ribosomal genes and nucleoli, respectively. All analysed individuals were collected in different natural populations in the Zona da Mata Mineira (Minas Gerais State, Brazil), of which 11 are located in the city of Viçosa (Amoras, Campus, Centro, Marrecos, Palmital, Paraíso, Silvestre, Vila. Cristal, Villa Chaves, Fundão and Barrinha), two in the city of Cajuri (Cajuri and Arraial Paraguai), one in the city of Coimbra (Coimbra), one in the city of Porto Firme (Nova Ilha) and one in the city of Piranga (piranga). Besides the Centro population, the eight first populations from Viçosa and the population of Porto Firme were sampled twice (1996-1998 and 1998-2002), while the populations located in Cajuri, Coimbra and Piranga, as well as Fundao and Barrinha (Viçosa), were studied only included in the second sampling. The results observed in the first stage of collections have revealed that, although in different frequency, all analysed populations possess B chromosomes. Among the Viçosa s populations, most bore females and males carried a B chromosome per haploid genome, the same dosage of standard (A) chromosomes. On the other hand, in Porto Firme, only 14.3% of individuals carried B chromosomes. Because one of the most conspicuous features of B chromosomes is their non-mendelian transmission mode, we hypothesized that at least in Viçosa, the B chromosomes of T. albitarse were regularizing their meiotic behaviour and, consequently, reaching their stabilization as a normal member of the normal chromosomal complement. To test this hypothesis, the stabilization process of B chromosomes was statistically quantified in all populations. In Porto Firme, the stabilization index (SI) of the B was sufficiently low, indicating a recent invasion. On the other hand populations from Viçosa carried a B per haploid genome, the SI value was equal to 100% while the other populations indicated a strong trend toward the stabilization of B chromosomes. A comparative analysis performed with both set of data (obtained in the first and second period of sampling) had supplied direct evidences of the invasive process of B in Porto Firme, where the B frequency has increased significantly. However in Viçosa, in spite of the increase in the metacentric B frequency and the significant reduction, in some populations, in the acrocentric B frequency, the general frequency of B chromosomes remained stable. The additional populations sampled showed B frequency and stability parameters similar to these observed in the Viçosa region, indicating that they are in a similar evolutionary stage, with most individuals carrying one B per haploid genome and high SI values. Fluorescent in situ hybridization (FISH) showed all ribosomal genes located in the heterochromatic arm of chromosome 14. The silver impregnation method was successfully applied in the nuc1eolar activity quantification of interfasic nuc1ei in males and females of T. albitarse. These results suggested that, despite the great variability in the size of ribosomal arm in this species, nuc1eolar activity is adjusted to the ploidy level

ASSUNTO(S)

vespa nucleolo citogenetica

ACESSO AO ARTIGO

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