Task partitioning, division of labour and nest compartmentalisation collectively isolate hazardous waste in the leafcutting ant Atta cephalotes

Abstract

We studied the organisation of garbage disposal and management in the leafcutting ant Atta cephalotes. The nest of this species has an internal garbage heap to which waste from the fungus garden is taken. The transport of waste from the fungus gardens to the garbage heaps is an example of task partitioning. Ninety-four percent of the garbage loads transferred from the fungus garden to the garbage heap were transferred indirectly via a caching site just outside the garbage heap entrance. A further 3% were transferred directly from a fungus garden worker to a garbage heap worker, again just outside the heap entrance. Only 3% were taken directly to the garbage heap without task partitioning. This is the first described example of task partitioning in insect societies for work other than foraging and the first example of task partitioning occurring entirely within the nest. Furthermore, there is a strong division of labour between the fungus garden workers and the garbage heap workers, with garbage workers hardly ever leaving the heap. Division of labour is reinforced by aggressive behaviour directed towards workers contaminated with garbage. This pattern of work organisation minimises contact between garbage heap workers, who are probably contaminated with pathogens hazardous to both the ants and their symbiotic fungus, and both fungus garden workers and the fungus garden. Task partitioning, division of labour (reinforced by aggression) and nest compartmentalisation act synergistically to isolate the hazardous garbage heap from the fungus gardens.

Mutualistic bacteria and a possible trade-off between alternative defence mechanisms in Acromyrmex leaf-cutting ants

“…In the present study we investigate whether caste differentiation in Acromyrmex leaf-cutting ants is also important with respect to the expression of different defence mechanisms against potentially infectious pathogens. Leaf-cutting ants employ a series of behaviours and chemicals to avoid the establishment and spread of pathogens in the colony, including workers actively cleaning the mutualistic fungus (Wilson, 1980;Currie and Stuart, 2001), and exhibiting effective waste management (Hölldobler and Wilson, 1990;Hart and Ratnieks, 2001). In addition, they produce chemical compounds with antibiotic properties in exocrine glands 1971;Maschwitz et al, 1970;do Nascimento et al, 1996;Ortius-Lechner et al, 2000;Poulsen et al, in review).…”

Differential resistance and the importance of antibiotic production in Acromyrmex echinatior leaf-cutting ant castes towards the entomopathogenic fungus Aspergillus nomius

“…Examples are: active cleaning (Wilson, 1980;Currie and Stuart, 2001), waste management (Hölldobler and Wilson, 1990;Bot et al, 2001a;Hart and Ratnieks, 2001), and the production of antibiotics by mutualistic bacteria (Currie, 2001;Currie et al 1999Currie et al , 2003Currie et al , 2006. Also important are the paired exocrine metapleural glands that are present in all but a few ant species (Hölldo-bler and Engel-Siegel, 1984).…”

Examination of the immune responses of males and workers of the leaf-cutting ant Acromyrmex echinatior and the effect of infection

“…Consequently, social insects have evolved a number of specialised mechanisms to defend their colonies against parasites, including grooming, antibiotic secretions and hygienic behaviour (e.g. Kermarrec et al, 1986;Rosengaus et al, 1998Rosengaus et al, , 2000Rosengaus et al, , 2004Schmid-Hempel, 1998;Christie et al, 2002;Hart and Ratnieks, 2001;2002;Hughes et al, 2002;Poulsen et al, 2002a,b;Turillazzi et al, 2004;Boomsma et al, in press). The effectiveness of these mechanisms is such that rather than the group-living lifestyle being associated with increased susceptibility to disease, as is expected, it may instead result in decreased susceptibility (Rosengaus et al, 1998;Hughes et al, 2002;Shimizu and Yamaji, 2003).…”