EFFECT OF THE CASTRATING TREMATODE PARASITE RHIPIDOCOTYLE-FENNICA ON ENERGY ALLOCATION OF FRESH-WATER CLAM ANODONTA-PISCINALIS

1. If host survival is important to a parasite, it should avoid the use of the host's maintenance energy. Selective use of the host's energy is possible by selecting which part of the host to penetrate and when to be active. 2. We study the effects of the castrating trematode parasite Rhipidocotyle fennica on energetics of fresh-water clam Anodonta piscinalis. 3. Before production of offspring, uninfected clams allocate energy to shell growth and glycogen storage. During offspring production shell growth slows down, clams lose weight and consume the stored glycogen. Concurrently the fat content of clams increases indicating the collection of long-term storage for maintenance during the winter. 4. Infected clams lack glycogen reserves and are lighter, but contain more fat than uninfected clams. Parasite reproduction occurs concurrently with the development of offspring in uninfected clams. During their reproduction, parasites use the energy that would otherwise be directed to host reproduction, without interfering with the maintenance energy of the host. Using only the reproductive energy is an efficient way to use the host without causing increased risk of mortality.