TY - JOUR
T1 - The origin of the chemical profiles of fungal symbionts and their significance for nestmate recognition in Acromyrmex leaf-cutting ants
AU - Richard, Freddie Jeanne
AU - Poulsen, Michael
AU - Hefetz, Abraham
AU - Errard, Christine
AU - Nash, David R.
AU - Boomsma, Jacobus J.
N1 - Funding Information:
Acknowledgements We thank A.N.M. Bot, S. Rønhede, and S.M. Mathiasen for the assistance with fungus culturing and obtaining the AFLP data; J.S. Pedersen and G. Nachman for statistical advice; C.R. Currie for providing some of the experimental lab colonies; P. D’Ettorre for comments on the manuscript; the Smithsonian Tropical Research Institute (STRI) for providing logistic help and facilities to work in Gamboa; and the Autoridad Nacional del Ambiente y el Mar (ANAM) for the permission to sample ant colonies in Panama and export them to Denmark. Fieldwork was supported by grants from the Carlsberg foundation and the Danish Natural Science Research Council to JJB. All experiments performed in this manuscript comply with current Danish and USA laws.
PY - 2007/9
Y1 - 2007/9
N2 - 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.
AB - 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.
KW - AFLP
KW - Basidiomycete
KW - Fungus-growing ants
KW - Gas chromatography
KW - Hydrocarbon profile
KW - Mutualism
KW - Symbiosis
UR - http://www.scopus.com/inward/record.url?scp=34547706014&partnerID=8YFLogxK
U2 - 10.1007/s00265-007-0395-1
DO - 10.1007/s00265-007-0395-1
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AN - SCOPUS:34547706014
SN - 0340-5443
VL - 61
SP - 1637
EP - 1649
JO - Behavioral Ecology and Sociobiology
JF - Behavioral Ecology and Sociobiology
IS - 11
ER -