Figure 1.
Our model of host-symbiont coevolution. Each host plays a genetically determined strategy, represented by color, and reproduces with probability proportional to its fitness derived from pairwise interactions with each of its symbionts. The new host offspring receives horizontally transferred symbionts from the other hosts (including the dying host—not shown). Whenever a host or symbiont reproduces, its offspring plays the same strategy as its parent, unless it mutates with probability μ.