Evolutionary ecology of immune defence in copepods

Abstract

Copepods are host to various species of parasites, but interactions of copepods with their parasites have rarely been studied in detail. In this review, first a brief introduction to the role of copepods as (intermediate) hosts of parasites is given and then the focus is on studies in the cyclopoid copepod Macrocyclops albidus and its tapeworm parasite Schistocephalus solidus. This host–parasite system has increasingly been studied for questions of ecology, behaviour and evolution of host–parasite interactions. To discuss the fundamental principles of such interactions, an approach based on ecological immunology was chosen, which is a new research area that aims at understanding causes of variation in immune defence in the light of ecology and evolution. Our studies indicate that the defence system of the copepod host is far more specific than is generally believed for invertebrates. This relates to a high degree of antigenic heterogeneity among the parasites, identified with the use of fluorescent lectins, which bind specific carbohydrate residues on the parasite surface. Natural selection on the parasite imposed by the copepod intermediate host might also be relevant for its virulence in the subsequent fish host. This implies that immunological interactions between hosts and parasites in their ecological context are potentially important aspects during host–parasite coevolution.