Rapid shifts in <Emphasis Type="Italic">Atta cephalotes</Emphasis> fungus-garden enzyme activity after a change in fungal substrate (Attini,Formicidae) |
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Authors: | P W Kooij M Schiøtt J J Boomsma H H De Fine Licht |
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Institution: | (1) Department of Biology, Centre for Social Evolution, University of Copenhagen, Universitetsparken 15, 2100 Copenhagen, Denmark;(2) Laboratory of Genetics, Plant Sciences Group, Wageningen University and Research Center, Droevendaalsesteeg 1, 6708 PB Wageningen, The Netherlands |
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Abstract: | Fungus gardens of the basidiomycete Leucocoprinus gongylophorus sustain large colonies of leaf-cutting ants by degrading the plant material collected by the ants. Recent studies have shown
that enzyme activity in these gardens is primarily targeted toward starch, proteins and the pectin matrix associated with
cell walls, rather than toward structural cell wall components such as cellulose and hemicelluloses. Substrate constituents
are also known to be sequentially degraded in different sections of the fungus garden. To test the plasticity in the extracellular
expression of fungus-garden enzymes, we measured the changes in enzyme activity after a controlled shift in fungal substrate
offered to six laboratory colonies of Atta cephalotes. An ant diet consisting exclusively of grains of parboiled rice rapidly increased the activity of endo-proteinases and some
of the pectinases attacking the backbone structure of pectin molecules, relative to a pure diet of bramble leaves, and this
happened predominantly in the most recently established top sections of fungus gardens. However, fungus-garden amylase activity
did not significantly increase despite the substantial increase in starch availability from the rice diet, relative to the
leaf diet controls. Enzyme activity in the older, bottom sections of fungus gardens decreased, indicating a faster processing
of the rice substrate compared to the leaf diet. These results suggest that leaf-cutting ant fungus gardens can rapidly adjust
enzyme activity to provide a better match with substrate availability and that excess starch that is not protected by cell
walls may be digested by the ants rather than by the fungus-garden symbiont. |
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