Visualization of the cost of specialization. Each point represents the value of the response index of an evolved parasite on its matched host (i.e. on the isofemale line it had evolved on) against the mean value on its three mismatched hosts. The response index is given as the relative difference between the infectivity of specialized parasites and the infectivity of generalist parasites tested on the same isofemale line. Specialization is costly if the parasites performing best on matched hosts perform worst on mismatched hosts.