Fig. 2
Facilitation between symbionts can occur within or between hosts. Small blue circles: facilitating symbionts; small green circles: facilitated symbionts; big yellow circle: co-infected host; big grey circle: uninfected host; rings: entry/exit point of the host; blue dashed arrows: facilitation; black solid arrows: transition between life cycle stages of the facilitated symbiont. Traits facilitated are categorised as ‘development’ (i.e. symbiont growth or differentiation) in the within-host environment, ‘infection success’ (i.e. host entry or establishment), ‘exit from the host’ at the interface between the within- and between-host environment, and ‘transmission’ in the between-host environment. Note that the diagram does not consider the symmetry of the interaction (i.e. the effect of the facilitated symbiont on the facilitator is not represented)
