Living in intermediate hosts: evolutionary adaptations in larval helminths.

In the complex life cycles of helminths, life in intermediate hosts poses special problems not covered by standard life history strategy theory. While under selection to reduce mortality and to increase growth, there is the additional problem of transmission between hosts. This review attempts to harmonise classical knowledge of the overall life cycle patterns with recent evolutionary theory as to how larval helminths exploit intermediate host tissues and avoid the gut to maximise fitness in terms of growth and mortality. It also considers the evolutionary rules by which trophically transmitted larvae are expected to increase their transmission rates to the next host.