l among distinct behavioural traits, or between the same trait expressed in different contexts) to provide a framework from which simple testable patterns of host behavioural changes can be predicted. Following infection, a manipulative parasite could (i) change the temporal consistency of its host’s behavioural responses, (ii) change the slope of a host reaction norm, i.e. the way host behavioural traits are expressed as a function of an environmental gradient, or (iii) decouple two or more host behavioural traits and/or change the way in which they correlate with each other. Two case studies involving trematode parasites and their freshwater hosts are used to provide empirical illustrations of the above scenarios. These clearly illustrate the full richness of behavioural alterations induced by parasites, and how these effects would go unnoticed using the classical trait-by-trait comparisons of mean values between parasitised and non-parasitised individuals. However, the power of animal personality and behavioural syndromes to inform research on host manipulation by parasites will only be fully realised when underlying mechanisms are elucidated and linked to their phenotypic impacts.
Multidimensionality in parasite-induced phenotypic alterations: ultimate versus proximate aspects
In most cases, parasites alter more than one dimension in their host phenotype. Although multidimensionality in parasite-induced phenotypic alterations (PIPAs) [FULL TEXT] seems to be the rule, it has started to be addressed only recently. Here, we critically review some of the problems associated with the definition, quantification and interpretation of multidimensionality in PIPAs. In particular, we confront ultimate and proximate accounts, and evaluate their own limitations. We end up by introducing several suggestions for the development of future research, including some practical guidelines for the quantitative analysis of multidimensionality in PIPAs.
Diversity and evolution of bodyguard manipulation
Among the different strategies used by parasites to usurp the behaviour of their host, one of the most fascinating is bodyguard manipulation. While all classic examples of bodyguard manipulation involve insect parasitoids, induced protective behaviours have also evolved in other parasite–host systems, typically as specific dimensions of the total manipulation. For instance, parasites may manipulate the host to reduce host mortality during their development or to avoid predation by non-host predators. This type of host manipulation behaviour is rarely described, probably due to the fact that studies have mainly focused on predation enhancement rather than studying all the dimensions of the manipulation. Here, in addition to the classic cases of bodyguard manipulation, we also review these ‘bodyguard dimensions’ and propose extending the current definition of bodyguard manipulation to include the latter. We also discuss different evolutionary scenarios under which such manipulations could have evolved.
How much energy should manipulative parasites leave to their hosts to ensure altered behaviours?
Although host manipulation is likely to be costly for parasites, we still have a poor understanding of the energetic aspects underlying this strategy. It is traditionally assumed that physiological costs are inevitably associated with mechanisms evolved by parasites to induce the required changes in host behaviours. While most energetic expenditures of parasites relate primarily to bringing about the altered behaviours, manipulative parasites also have to consider the condition of their host during the manipulation. Here, we suggest that because of this trade-off, the energy required to accomplish parasite-induced behaviours may represent a key energetic constraint for parasites. Depending on the energetic expenditures specific to each type of manipulation, parasites should undergo selection to secure resources for their host to allow them to perform manipulated behaviours.
What can parasitoid wasps teach us about decision-making in insects?
Millions