Preparation of mitotic chromosomes of leaf-cutting ants from the genera Atta and Acromyrmex

Abstract

Some modifications were made to the methodology of Imai et al. (Jpn. J. Genet. 63: 159-185, 1988) for cytogenetic analysis of the leaf-cutting ants Atta sexdens piriventris and Acromyrmex heyeri (Hymenoptera, Formicidae), shortening preparation time and improving chromosomal preparations. The brain ganglia of prepupae were dissected in a 0.0025% hypotonic solution of colchicine, placed on a glass slide on a cold plate (4 ± 1oC) for 20 min. The material was fixed directly on the cold slide (with cold fixative I), macerated with a histological needle and fixed again with fixative I, followed by fixatives II and III, all of them cold. The slide was flame-dried right after the use of fixative III, and it was allowed to air-dry at room temperature for 2 h. The resulting metaphases presented less contracted chromosomes, with separated and well defined sister chromatids at a high frequency, when the material was processed in the manner described and stained with 3% Giemsa in phosphate buffer (pH 6.8) for 15 min.<br>Objetivando uma melhor análise citogenética das formigas cortadeiras Atta sexdens piriventris e Acromyrmex heyeri, algumas modificações foram feitas no sentido de otimizar a metodologia de Imai et al. (Jpn. J. Genet. 63: 159-185, 1988), tendo-se conseguido a diminuição do tempo de preparo do material e melhor qualidade da preparação. O gânglio cerebral de pré-pupa foi dissecado em solução de colchicina hipotônica 0,0025% e colocado sobre lâmina de vidro (nova e previamente limpa para ser corada com Giemsa) com colchicina hipotônica. A lâmina foi colocada sobre placa de gelo (4 ± 1oC) por 20 min. O material foi fixado diretamente na lâmina (com fixador I gelado), macerado com agulha histológica e fixado novamente com fixador I, seguido dos fixadores II e III, todos gelados. A lâmina foi rapidamente flambada após a última fixação e foi deixada secar à temperatura ambiente por 2 h. As metáfases resultantes apresentaram, com maior freqüência, cromossomos menos contraídos, com cromátides irmãs separadas e bem definidas, quando o material foi processado como descrito acima e corado com solução de Giemsa 3% em tampão fosfato pH 6,8, por 15 min

Cytogenetic data on the threatened leafcutter ant Atta robusta Borgmeier, 1939 (Formicidae: Myrmicinae: Attini)

“…To date, chromosomal studies have been conducted in five taxa of leafcutter ants of the genus Atta. All presented 2n = 22 chromosomes, including the species collected in Brazil: A. bisphaerica, A. laevigata, A. sexdens rubropilosa [16,17], A. sexdens piriventris [18] and in Panama: A. colombica [19]. Data on chromosome banding are available for A. bisphaerica, A. laevigata, A. sexdens rubropilosa [17], and A. colombica [19].…”

The karyotypes ofGigantiops destructor(Fabricius) and other ants from French Guiana (Formicidae)

“…Th e karyotype has been described for only 10 species from fi ve Attini genera considered as basal, and their chromosome number varies from 2n = 12 to 2n = 54. On the other hand, the karyotypes for Acromyrmex and Atta species, both considered as the most derived attine genera (Wetterer et al 1998), are homogenous: Acromyrmex has 2n = 38, with the exception of the social parasite Acromyrmex ameliae Souza, Soares & Della Lucia with 2n = 36 (Barros, personal communication), and Atta with 2n = 22 Goñi et al 1983;Murakami et al 1998;Santos-Colares et al 1997).…”