Individual variation in an ectoparasite-host system: life history, fitness and evolutionary potential

Parasites are among the most ubiquitous and widespread living forms on earth exerting direct and indirect negative effects to the organisms they exploit. On their side, hosts try to reduce parasite burden through several adaptations. The dynamic and reciprocally exerted selective pressures make host-parasite interactions ideal systems for the study of coevolutionary processes and their effects on ecology. However, while the effects of parasites on host life history, defence strategies and evolution have been extensively investigated host-induced parasite evolution and life history were mainly neglected until recently. Furthermore, parasites have mostly been considered as agents of selection rather than as species in their own right. One of the most important characteristics of a species is its among- and within-individual variation in traits and overall performance as it is fundamental to respond to selective pressures (e.g. environmental variation) and generate adaptations. Nevertheless, the amount of variation for most parasite traits is unknown. Another crucial element defining the evolutionary ecology of a species is the relationship between its traits. In fact, the genetic architecture of traits and their phenotypic expression shape trade-offs, alternative life-history strategies, and trait evolutionary potential.