Environment can alter selection in host-parasite interactions.

Characteristics of hosts and parasites have a genetic basis, and thus can be shaped by coevolution. Infections measured under laboratory conditions have shown that the environment in which hosts and parasites interact might substantially affect the strength and specificity of selection. In addition, various components of host-parasite fitness are differentially altered by the environment. Despite this, environmental fluctuations are often excluded from experimental coevolutionary studies and theoretical models as 'noise'. Because most host-parasite interactions exist in heterogeneous environments, we argue that there is a need to incorporate fluctuating environments into future empirical and theoretical work on host-parasite coevolution.