Disease resistance in a weaver ant, <Emphasis Type="BoldItalic">Polyrhachis dives</Emphasis>, and the role of antibiotic-producing glands |
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Authors: | Peter Graystock William O H Hughes |
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Institution: | (1) Institute of Integrative and Comparative Biology, University of Leeds, Leeds, LS2 9JT, UK |
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Abstract: | Parasites represent one of the main threats to all organisms and are likely to be particularly significant for social animals
because of the increased potential for intragroup transmission. Social animals must therefore have effective resistance mechanisms
against parasites and one of the most important components of disease resistance in ants is thought to be the antibiotic-producing
metapleural gland. This gland is ancestral in ants, but has been lost secondarily in a small number of species. It is unknown
whether these evolutionary losses are due to a reduction in parasite pressure or the replacement of the gland’s function with
other resistance mechanisms. Here we used the generalist entomopathogenic fungus Metarhizium to compare the disease resistance of a species of a weaver ant, Polyrhachis dives, which has lost the metapleural gland, with that of the well-studied leaf-cutting ant Acromyrmex echinatior and two other ant species, Myrmica ruginodis and Formica fusca, all of which have metapleural glands. The P. dives weaver ants had intermediate resistance when kept individually, and similar resistance to A. echinatior leaf-cutting ants when kept in groups, suggesting that the loss of the metapleural gland has not resulted in weaver ants
having reduced disease resistance. P. dives weaver ants self-groomed at a significantly higher rate than the other ants examined and apparently use their venom for resistance,
as they had reduced resistance when their venom gland was blocked and the venom was shown in vitro to prevent the germination
of fungal spores. Unexpectedly, the leaf-cutting ant A. echinatior also had reduced resistance to Metarhizium when its venom gland was blocked. It therefore appears that the evolutionary loss of the metapleural gland does not result
in reduced disease resistance in P. dives weaver ants, and that this at least in part may be due to the ants having antimicrobial venom and high self-grooming rates.
The results therefore emphasise the importance of multiple, complementary mechanisms in the disease resistance of ant societies. |
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