Table 1.
Interaction models in one locus, two-allele models. The matching-alleles (MA) model is thought to represent interactions between hosts with the immune system and antigenic parasites, which have to specifically match the host in order to infect it. The gene-for-gene (GFG) type of interaction, inspired by interactions of plants with their pathogens, represents the situation where host needs to recognize specific ‘effectors’ of the parasite in order to launch its defence, hence here matching is equivalent to resistance. Mutations both in the host and the parasite would lead to the lack of such recognition, and hence to infection. Therefore, the parasite population consists of specialists (parasite allele A can only infect host A) and generalists (parasite B can infect any host allele). Above, sH denotes the relative fitness cost of the host owing to parasitic infection, sP denotes the relative fitness cost of the parasite for the inability to infect the host. We assume that 0 < sH < 1 and 0 < sP < 1.
| host fitness | host A | host B | parasite fitness | host A | host B |
|---|---|---|---|---|---|
| MA model | |||||
| parasite A | 1 − sH | 1 | parasite A | 1 | 1 − sP |
| parasite B | 1 | 1 − sH | parasite B | 1 − sP | 1 |
| GFG model | |||||
| parasite A | 1 | 1 − sH | parasite A | 1 − sP | 1 |
| parasite B | 1 − sH | 1 − sH | parasite B | 1 | 1 |