Quand virus et hôtes évoluent ensemble : la fidélité est-elle la règle ?

Viruses display strong interactions with their hosts, from physiological and ecological point of views, often leading to strict patterns of host specificity. It is then tempting to consider that viruses evolve in the same way as their hosts, behaving more or less like hosts' characters. However, the cospeciation between viruses and their hosts, that is the degree to which their evolutionary trees are similar, has been the subject or relatively few studies, in a field otherwise very dynamic. The main concepts and methods to study the patterns of cospeciation, and more generally cophylogeny, are reviewed here. Their uses with host-virus systems suggest that, contrarily to a common belief, the joint evolutionary history of viruses and their hosts is often complex. Without a rigorous cophylogeny study, it is then very risky to consider that the evolutionary history of viruses mirrors that of their hosts.