Coevolutionary dynamics between hosts and transmissible cancers, and evolution of sex.
(A) Sensitivity of the population genetic models to the selection coefficients (shost,scancer) and to the proportion of transmissible neocancers that are recently derived from the original host (α). Red lines delimit the parameter spaces leading to non-steady and steady coevolutionary dynamics in the three-locus model (plain line; found numerically) and in the simplified one-locus model (dashed line; found analytically in S1 Appendix). In the three-locus model, the dynamic is defined as ‘steady’ when the variance in genotypic frequencies over 500 time steps is below 10−10. Dark purple indicates conditions under which a modifier allele associated with sexual reproduction (and with recombination, at least for one of the recombination rates tested) can invade in the three-locus model in at least one of the 100 simulation runs. The code used to perform this sensitivity analysis can be found in S1 Source Code. (B-C) Examples of non-steady and steady coevolutionary dynamics in the three-locus model. The linkage disequilibrium in the host is calculated as , i.e., a positive linkage disequilibrium here represents a non-random excess of allele combinations ab and AB. In (B) and (C), parameter values are: shost = 0.5, scancer= 0.8, and α = 0 (B) or α = 0.1 (C).