Actinomicetos e fungos simbiontes: implicações para formigas cortadeiras do gênero Acromyrmex MAYR, 1865

• Autor(a) principal: Dângelo, Rômulo Augusto Cotta
• Data de Publicação: 2011
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/3935
• topic: Acromyrmex; Actinomicetos; Simbiose; Inibição; Defesa; Acromyrmex; Actinomycetes; Symbiosis; Inhibition; Defense; CNPQ::CIENCIAS BIOLOGICAS::PARASITOLOGIA::ENTOMOLOGIA E MALACOLOGIA DE PARASITOS E VETORES

Social insects are subjected to a great variety of pathogens, and those who is constantly in contact with the soil, as the ants and the térmites, are more susceptible to parasites and diseases. During the course of the evolutionary history, social insects developed many machanisms to avoid the contamination by fungi and other parasites. Leaf-cutting ants are sobjected to a variety off ungi that can affect individuals of the colony or the symbiotic basidiomycete fungus Leucoararicus gongylophorus, which is used as the primary source of nutrients for these insects. Some of these pathogens are parasitic fungi of the fungus garden of the genus Escovopsis. Recent reseach suggests that these ants show a second mutualist group, actinomycetes of the genus Pseudonocardia that produce secondary metabolites with specific antimicrobial properties against Escovopsis. Also, according with these studies, these actinomycetes are housed in specialized structures in the integument of the leaf-cutting ants, where they receive nutrients through exogenous glands, which would allow the development of these microrganisms. Thus, the objectives of this work were: 1) isolate actinomycetes strains and evaluate the degree of inhibition of these organisms on the fungi present in colonies of leaf-cutting ants of the genus Acromyrmex collected in Viçosa-MG; 2) identify and verify the similarity degree of different strains of symbiotic actinomycetes present in ants of the same genus; 3) verify the presence of specialized structures that could harbor actinomycetes in three species of leafcutting ants; e 4) determine the implication of the absence of these structures for these ants. In the inhibition tests, actinomycetes of five species of the genus Acromyrmex was isolated and inhibition was measured against the four more common fungi found in the body of these same kinds of ants, as well as Escovopsis sp., during 10 days. Analyzing different symbiotic actinomycetes strains isolated from leaf-cutting ants, it was found that, depending on this strain, there may be na an antibiotic or a stimulatory effect against fungi, enthomopathogenic or not. It was concluded that increases and decreases in the rates of inhibition throughout the days may be related to the role that secondary metabolities have on fungus. Molecular markers were used to identify six actinomycetes obtained from five species of leaf-cutting ants. Five species of two genera of these microrganisms could be identified: Streptomyces, isolated from the ant Ac. balzani and four different Pseudonocardia strains, obtained from other species evaluated. Finally, in order to verify the presence of specialized structures that could harbor actinomycetes and determine the implications of its absence, histological sections were performed on workers of different sizes of the species Ac. disciger, Ac. subterraneus subterraneus and social parasite Ac. ameliae. In addition, the proportional size of the metapleural gland in these three species was compared. It was found that workers of different sizes of the species of leaf-cutting ants studied do not have any specialized cavity where it is possible the allocation of actinomycetes in the head, thorax or gaster. In the specie Ac. subterraneus subterraneus is possible that exocrine glands release their secretions directly in the surface of the tegument, allowing the presence of the actinomycetes in these locations. Although Ac. disciger does not have a visible layer of actinomycete on the body, this specie feature lots of hair, as well as the largest metapleural gland among the analyzed species. Ac. ameliae, also, has no coat of actinomycetes on the body, and possibly direct its energy in parasite the colonies and explore the defenses of its host. Thus, there may be a trade off between the different defense strategies employed by the leaf-cutting ants.