6533b853fe1ef96bd12ad78d

RESEARCH PRODUCT

Bird and amphipod parasites illustrate a gradient from adaptation to exaptation in complex life cycle.

subject

description

6 pages; International audience; Trophically transmitted parasites modify the phenotype of their hosts, sometimes in a way that facilitates transmission. Parasite-induced changes can be either part of a manipulative strategy evolved to improve the transmission success of the parasite, or simply by-products of infection with no health effect. In the former case, manipulation is regarded as a parasite adaptation driven by the probability of being eaten by a suitable next host. Here, we consider the fact that manipulation may also be an 'exaptation': a trait that evolved for a certain use, but which has been co-opted for a new use. According to this view, features built by natural selection for their role (historical genesis) and current utility features at present enhancing fitness of the parasite are different. We describe the behavioural profile of a freshwater crustacean (Gammarus roeseli) when serving as intermediate host to an acanthocephalan parasite (Polymorphus minutus). Although host manipulation by P. minutus is assumed to favour predation by avian definitive hosts (current utility feature), its evolution has been driven by the probability of dying inside non-host predators (historical genesis). This example of an exaptation, taken together with examples of adaptations in closely related host-parasite associations, improves our understanding of the evolutionary genesis of parasites' transmission strategies.