 systems fits the current view of manipulation as being multidimensional. The benefits in combining ethopharmacology with more recent molecular tools to investigate candidate neuromodulatory pathways is also emphasized. We conclude by discussing the value of a multidisciplinary study of parasitic manipulation, combining evolutionary (parasite transmission), behavioural (syndrome of manipulation) and neuroimmunological approaches.
Pathways to understanding the extended phenotype of parasites in their hosts
The study of the adaptive manipulation of animal behavior by parasites is entering very exciting times. Collectively the field has moved from its important and instructional natural history phase into proximate-level studies aiming to elucidate the mechanisms by which one organism controls another. Because many cases studies involve cross-kingdom control of behaviour, the findings are sure to be exciting. In this review I examine what possible pathways we can take to understanding the controlling behavior of parasites and how host behavior has become an extended phenotype of the parasites that is often hidden from view.
Host–parasite molecular cross-talk during the manipulative process of a host by its parasite
Many parasite taxa are able to alter a wide range of phenotypic traits of their hosts in ways that seem to improve the parasite’s chance of completing its life cycle. Host behavioural alterations are classically seen as compelling illustrations of the ‘extended phenotype’ concept, which suggests that parasite genes have phenotype effects on the host. The molecular mechanisms and the host–parasite cross-talk involved during the manipulative process of a host by its parasite are still poorly understood. In this Review, the current knowledge on proximate mechanisms related to the ‘parasite manipulation hypothesis’ is presented. Parasite genome sequences do not themselves provide a full explanation of parasite biology nor of the molecular cross-talk involved in host–parasite associations. Recently, first-generation proteomics tools have been employed to unravel some aspects of the parasite manipulation process (i.e. proximate mechanisms and evolutionary convergence) using certain model arthropod-host–parasite associations. The pioneer proteomics results obtained on the manipulative process are here highlighted, along with the many gaps in our knowledge. Candidate genes and biochemical pathways potentially involved in the parasite manipulation are presented. Finally, taking into account the environmental factors, we suggest new avenues and approaches to further explore and understand the proximate mechanisms used by parasite species to alter phenotypic traits of their hosts.
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