Abstract
This chapter explores questions that have emerged from the ongoing quest for patterns and processes in the evolution of host behaviour manipulation by parasites. The arguments are developed in three segments. The chapter begins with a discussion of the three main evolutionary routes that can lead to host manipulation: the manipulation sensu strict, the mafia-like strategy, and the exploitation of compensatory responses. This is followed by a perspective on variations in the intensity and frequency of phenotypic changes observed in parasitized hosts within a given host–parasite association. The chapter reviews the genetic and environmental causes of variability in host behaviour manipulation and identifies a number of potential, but poorly studied, sources of variability (parasitic load, host and parasite ontogeny, seasonality, etc). It concludes with a discussion on the ability of parasites to alter multiple characteristics of their host's phenotype.