Effects of the fungus Syncephalastrum (Mucorales: Syncephalastraceae) in nests of leafcutter ants (Formicidae: Attini)

• Ano de defesa: 2020
• Autor(a) principal: Bautz, Keminy Ribett
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Universidade Federal de Viçosa
• Palavras-chave em Português: Formiga-cortadeira; Fungos; Microrganismos; Relação hospedeiro-parasita; Entomologia Agrícola
• Link de acesso: https://locus.ufv.br//handle/123456789/28916

Leafcutter ants form a symbiotic nutritional mutualism with a basidiomycete fungus, growing in fungus gardens. This symbiosis interacts naturally with a range of microrganisms including some fungi that may be antagonist. Among these is the fungus Syncephalastrum, which is considered a pathogen of the fungus garden. Studies of the effects of potentially antagonist fungi on the ant-fungus mutualism are mostly performed in colonies in the absence of the queen, which may result in unrealistic conclusions about the negative effects of the fungi on the mutualist. Thus, the present study aimed to investigate the effects of Syncephalastrum sp. in the fungus garden of colonies of the leafcutter ant Acromyrmex subterraneus subterraneus in two levels of colony complexity (presence and absence of the queen). We tested the following hypothesis: that although Syncephalastrum sp. is found naturally in healthy colonies, it can cause negative effects to colonies when we apply a high concentration of its spores to the colony. Further, we hypothesized that the negative effects increase with reduced colony complexity. Thus, colonies of leafcutter ants of the species Ac. subterraneus subterraneus were divided into two levels of complexity: queenright colonies (fungus garden, queen and workers) and queenless colonies (fungus garden and workers). They were inoculated with spores of Syncephalastrum sp. or blank controls. Dependent variables measured were weight – leaves cut by ants; midden production; colony weight; presence of Syncephalastrum sp. in the midden; and survival of colonies. Our results showed that, in general, Syncephalastrum sp. negatively affected leaf cutting, waste production and the weight of colonies, with effects greater in queenless colonies. These effects, however, were not enough to compromise the survival of these colonies – all queenright and queenless colonies survived the experimental period of 28 days and indeed 96 days after that when maintained in the laboratory. To conclude, the isolate of Syncephalastrum sp. used in the present study caused negative effects to colonies of the leafcutter ant Ac. subterraneus subterraneus but did not compromise the survival of the colonies. However, our results highlight the importance of each element (fungus garden, queen and workers) in the symbiosis of leafcutter ants, mainly in studies that investigate the effect of antagonist microrganisms on leafcutter ant’s fungal cultivars. Keywords: Leafcutter ant. Fungus garden. Microrganisms. Host-parasite interactions. Acromyrmex. Leucoagaricus gongylophorus.