 
Summary: 1
Supporting Information 2. Analytical approximation of selection coefficients
generated by hostparasite coevolution.
Intuitively, hostparasite coevolution in which offspring are biased towards encountering
parasites transmitted by their own mothers should result in both genotypic and similarity
selection. Here I describe how to calculate the selection generated in an onelocus host
parasite model in terms of the selection coefficients used in the singlespecies model
presented in the main text (i.e., equation 1).
First, I determine the relationship between the selection coefficients and the
fitnesses of different offspring/mother combinations. Let wi,j be the fitness of an offspring
of genotype i from a mother of genotype j. Using the singlespecies fitness function
given by equation 1, multiplied by a scaling factor K, we obtain a set of equations relating
fitnesses to selection coefficients: wAA,AA = K(1 A), wAA,Aa = K(1 a), wAa,AA = K(1
a), wAa,Aa = K(1 a)(1 a)(1 A)(1 A,a), wAa,aa = K(1 a)(1 a)2
(1 A)(1
A,a), waa,Aa = K((1 a)2
+ A)(1 a), and waa,aa = K((1 a)2
+ A)(1 a)2
(1 A)(1
A,a)2
