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Garden substrate preparation behaviours in fungus-growing ants

Published online by Cambridge University Press:  02 April 2012

D.M. Mangone
Affiliation:
Department of Ecology and Evolutionary Biology, University of Kansas, Lawrence, Kansas 66045, United States of America
C.R. Currie*
Affiliation:
Department of Ecology and Evolutionary Biology, University of Kansas, Lawrence, Kansas 66045, United States of America and Department of Bacteriology, University of Wisconsin–Madison, Wisconsin 53706, United States of America
*
2 Corresponding author (e-mail: [email protected]).

Abstract

Fungus-growing ants (Hymenoptera: Formicidae: tribe Attini) engage in mutually beneficial symbioses with fungi (Basidiomycota) that serve as their main food source. The leaf-cutters (genera Acromyrmex Mayr and Atta Fabricius), the most derived attine ants, employ elaborate nest-hygiene behaviours, including substrate preparation. By preparing substrate prior to its incorporation into the fungus garden, workers facilitate the physical breakdown of leaf material while reducing the abundance of potentially harmful microbes that contact their fungal mutualist. Despite its importance in ant fungiculture, substrate preparation has not been investigated in other genera of fungus-growing ants. We examined substrate-preparation procedures used by five genera of fungus-growing ants (Apterostigma Mayr, Cyphomyrmex Mayr, Trachymyrmex Forel, Acromyrmex, and Atta) representing most of the phylogenetic range of the Attini. Behavioural observations revealed that all five genera engage in substrate-preparation behaviours. Furthermore, these behaviours vary by genus, with Trachymyrmex, Acromyrmex, and Atta engaging in more elaborate preparation behaviours than the other genera. Additionally, we found that during substrate preparation, leaf-cutting ants inoculate leaf fragments with actinomycetous bacteria. These filamentous bacteria are known to produce antibiotics that suppress fungal pathogens, which suggests that inoculation with the bacterial mutualist during substrate preparation helps protect the fungus gardens of leaf-cutter ants from these parasites. Our finding that substrate-preparation behaviours occur across the phylogenetic range of attine ants suggests that these behaviours are a critical component of successful fungiculture by ants.

Résumé

Les fourmis champignonistes (Hymenoptera: Formicidae: tribu Attini) établissent une symbiose mutuellement bénéfique avec les champignons (Basidiomycota) qui constituent leur principale source de nourriture. Les coupeuses de feuilles (des genres Acromyrmex Mayr et Atta Fabricius), les fourmis les plus évoluées des Attini, utilisent des comportements hygiéniques complexes, en particulier la préparation des substrats. En préparant le substrat avant son incorporation à la culture de champignons, les ouvrières facilitent la décomposition physique du matériel foliaire, tout en réduisant l’abondance des microorganismes potentiellement dangereux qui entrent en contact avec le champignon symbiotique. Malgré l’importance de la préparation des substrats dans la fongiculture des fourmis, personne ne l’a étudiée chez les autres genres de fourmis champignonistes. Nous examinons ici les procédures de préparation des substrats chez cinq genres de fourmis champignonistes (Apterostigma Mayr, Cyphomyrmex Mayr, Trachymyrmex Forel, Acromyrmex et Atta), qui représentent l’essentiel de la gamme de diversité phylogénétique chez les Attini. Des observations comportementales montrent que les cinq genres possèdent tous des comportements de préparation des substrats. De plus, ces comportements varient d’un genre à l’autre et ce sont Trachymyrmex, Acromyrmex et Atta qui ont les comportements de préparation les plus élaborés. Aussi, durant la préparation des substrats, nous avons observé les fourmis coupeuses de feuilles inoculer les fragments de feuilles de bactéries actinomycètes. Ces bactéries filamenteuses sont connues pour leur production d’antibiotiques qui inhibent les pathogènes des champignons, ce qui laisse croire que l’inoculation de cette bactérie symbiotique durant la préparation des substrats aide à protéger les cultures de champignons des fourmis coupeuses de feuilles de leurs parasites. Notre observation des comportements de préparation des substrats dans tout l’éventail phylogénétique des fourmis de la tribu Attini indique que ces comportements sont une composante essentielle d’une fongiculture réussie chez les fourmis.

[Traduit par la Rédaction]

Type
Articles
Copyright
Copyright © Entomological Society of Canada 2007

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