Experiment 2: nest hygiene
Sixty weaver ants (30 ants per colony) were collected from
within the nest. Half of the ants from each colony had their
venom gland blocked with nail varnish and half had a control
treatment on the pronotal spines, for a total of 30 replicates per
treatment. One hundred twenty leaf-cutting ant workers (40
ants per colony) were collected from the outer surface of the
fungal crop. The ants from each colony were divided evenly
into the four blockage treatments as follows: (1) varnish
applied to the pronotal spines as a control, (2) metapleural
gland blocked, (3) venom gland blocked, or (4) both venom
and metapleural glands blocked, with a total of 30 replicates
per treatment. Each ant was placed in a pot with a 10-mm2
section of either the silk nest material of weaver ants or the
fungal garden of leaf-cutting ants, fromtheir original nest, and
balls of cotton wool moistened with water and sucrose solution
at 26 °C and 80 % RH. Thirty further 10 mm2 sections of
nest material were set up identically for each species, except
no ant was placed in the pot (Fig. S2). The nest substrate was
monitored for 15 days for the appearance of any foreign
fungus and death of the fungal crop. If a worker died during
the experiment, then it was replaced with an identically treated
worker.
To identify the fungi that developed in the leaf-cutting ant
trials, three representative samples of each fungal morphotype
(based on external morphology, spore structure, and color)
were isolated on malt extract agar plates at 30 °C until the
fungi produced conidia, and then stored at 4 °C. DNA was
extracted from the samples by adding 200 μl of 5 % Chelex
solution (in 10 mM Tris buffer) and 0.05 g of 0.1 mm silica
beads to approximately 0.05 g of the sample fungus and
placed in a QIAGEN TissueLyser BeadBeater for 4 min at
50 oscillations/s. Samples were then incubated at 90 °C before
being centrifuged for 30 min at 4 °C. Supernatant from the
samples was cleaned with OneStep-96 Polymerase Chain
Reaction (PCR) Inhibitor Removal Kit (Zymo Research) prior
to PCR amplification of the internal transcribed spacer regions
1 and 2 with the primers ITS1 and ITS4 (Henry et al. 2000;
Foley et al. 2012). PCR products were sequenced and fungi
were identified by BLASTn searches of the resulting