Frontiers in host-parasite ecology and evolution.
Host–parasite interactions have long been recognized as a major force in ecology (Elton 1927) and evolution (Haldane 1949). The effects of parasitism are considered instrumental in influencing fundamental aspects of host biology, including host behaviour, the evolution of sex, variation in mating systems and life history strategies, sex ratio variation, population regulation, invasion dynamics, the maintenance of genetic diversity and the evolution of immune genes and organization of immunological responses (Anderson & May 1978; Hamilton 1980; Poulin 2007; Schmid-Hempel 2010). Conversely, the fitness of a parasite is completely dependent on its success at infecting and reproducing in a host and so interactions with the host can determine the size of parasite populations and shape the evolution of parasite genomes. These antagonistic interactions have taken centre stage in much of ecological and evolutionary theory and this position will be enhanced as postgenomics resources and technologies are utilized to explore the causes and consequences of host–parasite interaction. In this special issue, we highlight emerging areas of research in host–parasite ecology and evolution that are enabled by novel molecular and postgenomic approaches, including work in natural systems of ecological relevance. For vertebrates, the need to defend against infection has given rise to the complexity of the adaptive immune system, with different arms of the immune system activated in response to different types of infection (e.g. viral, bacterial or helminthic), and with cytokine signalling molecules mediating the regulation of these different immune arms. While medical and laboratory immunologists have developed assays that provide tremendous mechanistic insight into the com-