Fig. 4
Proposed experimental design to test the evolution of facilitation. a Experimental design required to measure evolved responses to facilitation. Small green circles: facilitated symbionts (FD); small blue circles: facilitator symbionts (FR); big grey circles: hosts. Bold coloured arrows: (co)evolving players; thin black arrows: naive players (i.e. introduced from a naive base population at each generation). Treatments: (i) evolution of the facilitator in single infections: FR(ES); (ii) evolution of the facilitator in multiple infections: FR(EM); (iii) coevolution of the facilitated and facilitator in multiple infection: FR(CM) and FD(CM), respectively; (iv) evolution of the facilitated in multiple infections: FD(EM); (v) evolution of the facilitated in single infections: FD(ES). b Example of a possible evolved response of local adaptation in which facilitated symbionts have higher fitness when assayed in the infection environment in which they evolved. (1) Facilitation; (2) adaptation to the presence of a facilitator; (3) adaptation to the presence of a coevolved facilitator; (4) cost of adaptation to the facilitator; (5) local adaptation to either a coevolved or evolved facilitator
