Figure 15.21 Coevolution of Australian rabbits and the Myxoma virus. In rabbit populations that had never been exposed to the virus, nearly all infected rabbits died. However, a small percentage of resistant rabbits survived and passed on their resistant genes to the next generation. At the same time, selection favored less lethal virus strains, which could reproduce and get transmitted by mosquitoes that only feed on live rabbits. Since rabbit populations evolved higher resistance and viruses evolved to be nonlethal, rabbit populations that experienced more epidemics of the disease experienced less mortality.

Data from F. Fenner and F. N. Ratcliffe, Myxomatosis (Cambridge University Press, 1965).