Figure 2. Acquisition timing.

a) All set-ups contained one focal pupa, 4 minor workers and a piece of fungus garden. Major workers with visible exosymbiont were added at varying intervals from 0–1 hours to 24–30 hours post-eclosion. Controls contained major workers added at the time of subcolony set-up. Ants acquired in a gradient from 100% of controls to 0% of ants exposed after more than 2 hours. Drawings modified from Poulsen et al. 2003 and photos by S.E.M. b) Critical window period for exosymbiont acquisition in Acromyrmex octospinosus. The percentage of ants acquiring visible exosymbiont after exposure to exosymbiont-carrying majors introduced at varying times after eclosion. All pupae from 3–4 hour subcolonies died (n = 10), not shown. Sample sizes (n) represent the number of focal ants surviving more than five days after eclosion. See Figure S1 for mortality data. *An additional 11 subcolonies were set up in the lab due to high field mortality.