Interpreting multidimensionality in parasite-induced phenotypic alterations: panselectionism versus parsimony

摘要

The purpose of this note is to provide an alternative to the interpretation of multidimensionality in parasite-induced phenotypic alterations as a set of effectively-independent traits produced by adaptive evolution. We propose here that infection with so-called 'manipulative parasites' typically results in an 'infection syndrome', characterized by several distinctive symptoms corresponding to the alteration of particular phenotypic traits in infected hosts. Based on the available physiological evidence, we argue that symptoms might actually be the consequence of the dysregulation of some key neuromodulator, arising as a byproduct of the subversion of the host's immune system by the parasite. In that respect, it might be inadequate, from a functional point of view, to separate phenotypic effects that appear to increase trophic transmission from those that do not. We suggest that future research should test the validity of the 'infection syndrome' hypothesis through focusing on the mechanisms involved in multidimensionality at the intraspecific level, and through looking for the existence of non-random associations between symptoms at the interspecific level, across host-parasite associations.