The origin of the chemical profiles of fungal symbionts and their significance for nestmate recognition in <Emphasis Type="Italic">Acromyrmex</Emphasis> leaf-cutting ants |
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Authors: | Freddie-Jeanne Richard Michael Poulsen Abraham Hefetz Christine Errard David R Nash Jacobus J Boomsma |
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Institution: | (1) Institut de Recherche sur la Biologie de l’Insecte, CNRS UMR 6035, Faculté des Sciences, Parc de Grandmont, 37200 Tours, France;(2) Department of Population Biology, Institute of Biology, University of Copenhagen, 2100 Copenhagen, Denmark;(3) Department of Zoology, Tel Aviv University, Ramat Aviv, 69978 Tel Aviv, Israel;(4) Present address: Department of Entomology, North Carolina State University, Raleigh, NC 27695, USA;(5) Present address: Department of Bacteriology, University of Wisconsin-Madison, 420 Henry Mall, Madison, WI 53706, USA |
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Abstract: | Cuticular hydrocarbon profiles are essential for nestmate recognition in insect societies, and quantitative variation in these
recognition cues is both environmentally and genetically determined. Environmental cues are normally derived from food or
nest material, but an exceptional situation may exist in the fungus-growing ants where the symbiotic fungus garden may be
an independent source of recognition compounds. To investigate this hypothesis, we quantified the chemical profiles of the
fungal symbionts of 18 sympatric colonies of Acromyrmex echinatior and Acromyrmex octospinosus and evaluated the quantitative variation of the 47 compounds in a multivariate analysis. Colony-specific chemical profiles
of fungal symbionts were highly distinct and significantly different between the two ant species. We also estimated the relative
genetic distances between the fungal symbionts using amplified fragment length polymorphism (AFLP) and correlated these with
the overall (Mahalanobis) chemical distances between the colony-specific profiles. Despite the standardized laboratory conditions,
the correlations were generally weak, but a statistically significant portion of the total variation in chemical profiles
could be explained by genetic differences between the fungal symbionts. However, there was no significant effect of ant species
in partial analyses because genetic differences between symbionts tend to coincide with being reared by different ant species.
However, compound groups differed significantly with amides, aldehydes, and methyl esters contributing to the correlations,
but acetates, alkanes, and formates being unrelated to genetic variation among symbionts. We show experimentally that workers
that are previously exposed to and fed with the fungal symbiont of another colony are met with less aggression when they are
later introduced into that colony. It appears, therefore, that fungus gardens are an independent and significant source of
chemical compounds, potentially contributing a richer and more abundant blend of recognition cues to the colony “gestalt”
than the innate chemical profile of the ants alone.
Freddie-Jeanne Richard and Michael Poulsen contributed equally to this work. |
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Keywords: | Fungus-growing ants Basidiomycete Symbiosis Mutualism Hydrocarbon profile Gas chromatography AFLP |
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