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Juiz de Fora, Brazil

Tranter C.,University of Sussex | Graystock P.,University of Sussex | Shaw C.,University of Leeds | Lopes J.F.S.,Campus Universitario Of Martelos | Hughes W.O.H.,University of Sussex
Behavioral Ecology and Sociobiology | Year: 2014

Social groups are at particular risk for parasite infection, which is heightened in eusocial insects by the low genetic diversity of individuals within a colony. To combat this, adult ants have evolved a suite of defenses to protect each other, including the production of antimicrobial secretions. However, it is the brood in a colony that are most vulnerable to parasites because their individual defenses are limited, and the nest material in which ants live is also likely to be prone to colonization by potential parasites. Here, we investigate in two ant species whether adult workers use their antimicrobial secretions not only to protect each other but also to sanitize the vulnerable brood and nest material. We find that, in both leaf-cutting ants and weaver ants, the survival of the brood was reduced and the sporulation of parasitic fungi from them increased, when the workers nursing them lacked functional antimicrobial-producing glands. This was the case for both larvae that were experimentally treated with a fungal parasite (Metarhizium) and control larvae which developed infections of an opportunistic fungal parasite (Aspergillus). Similarly, fungi were more likely to grow on the nest material of both ant species if the glands of attending workers were blocked. The results show that the defense of brood and sanitization of nest material are important functions of the antimicrobial secretions of adult ants and that ubiquitous, opportunistic fungi may be a more important driver of the evolution of these defenses than rarer, specialist parasites. © 2013 Springer-Verlag Berlin Heidelberg.

Lopes J.F.S.,Campus Universitario Of Martelos | Ribeiro L.F.,Campus Universitario Of Martelos | Brugger M.S.,Campus Universitario Of Martelos | Brugger M.S.,Laboratorio Of Insetos Sociais Praga | And 3 more authors.
Sociobiology | Year: 2011

Ant nests vary in their depth and internal complexity. They can be shallow or reach seven meters down into the soil, with many chambers connected by tunnels. In the case of leaf-cutting ants, the nest protects the colony and provides appropriate microclimate conditions for the ants and the symbiotic fungus garden. In the present study we compared the internal architecture and population size of Acromyrmex subterraneus molestans nests in an urban and a rural area. We excavated, molded and measured six nests in an urban area and five nests in a rural area. For each nest, we measured the total volume of fungus in the chambers and estimated the population by counting the workers, which were separated into four size classes. The nests of A. subterraneus molestans in the urban and rural areas were always found near the base of trees. In the urban area they were also found near the curb of sidewalks. Ants use old roots and debris to reinforce the structure of the nest tunnels and at the same time reduce the costs of excavation by taking advantage of pre-existing cavities. Nests from the rural area had only one chamber, whereas in the urban area they had up to four chambers. Fungus chambers showed non-defined shapes and were found near the soil surface, both in the urban and in the rural area. Closeness to the surface may pose a problem to the maintenance of the humidity levels required by the fungus garden. The accumulation of cut leaves over the nest, as observed for other species of leaf-cutting ants, in particular A. crassispinus, may be a strategy to solve this problem. Building superficial nests also helps reduce the costs of excavating, and saves energy in the transport of substrate to the fungus chamber. The nest tunnels were located in pre-existingcavities and almost always connected the external environment to the fungus chamber. There were also longer tunnels that opened at some distance from the nest. These tunnels allow an increase in the foraging area and reduce the risk of outside prédation. With respect to population size, we noted that the small workers represented on average 50% of the population, with no difference between the proportion of workers of each size class between urban and rural nests. No significant differences were found in the volume of fungus between nests of the urban and rural area. There were no significant correlations between the volume of fungus and the total population of workers or the number of workers of each size class.

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