Ectoparasite susceptibility in lizards from populations sympatric and allopatric with ticks

Theory suggests that host-parasite interaction should lead to local adaptation of parasites to their hosts and vice versa. The degree of local adaptation depends on, for example, migration, relative generation time of host and parasite, and the number of host species. Furthermore, in any coevolutionary process, local adaptation of one species is dependent on the evolution of sympatric and allopatric populations of the other species, and the degree of gene flow. The tick Ixodes ricinus is a generalist tick feeding on hosts of a variety of taxa. We contrasted populations of common lizards (Lacerta vivipara) differing in their evolutionary history of exposure to ticks. Juvenile lizards were raised in a common garden experiment. We monitored growth rate, physiological performance, and aspects of immune function in tick-exposed and control offspring. There were no differences in response to tick infestation between host populations, with both sympatric and allopatric hosts showing impaired growth and endurance under parasite exposure. Ticks were marginally more engorged on allopatric hosts (P = 0.06); hence, our results do not support the hypothesis of local adaptation of parasites.