Increased parasite abundance associated with reproductive maturity of the clam Anodonta piscinalis

Several studies on vertebrates have demonstrated that reproductive activiti es may increase the parasite load, but this has not been shown in invertebr ate hosts. We studied abundance of a potentially harmful gill parasite, the ergasilid copepod Paraergasilus rylovi, from the freshwater bivalve host A nodonta piscinalis in relation to reproductive maturity of the host in the field. Prevalence of this previously unstudied parasite varied from 90 to 1 00%, and the mean parasite abundance from 16.3 to 28.8 among 3 study popula tions. Abundance of P. rylovi increased with host size. In the maturating a ge groups (3-5 yr) the length-adjusted mean parasite abundance among mature , reproducing female clams that brooded glochidia larvae was 2 times higher than in nonreproducing females, the observed pattern being consistent amon g the 3 study lakes. Alternative, mutually nonexclusive explanations may be found for the result. For example, changes in clam behavior or filtration activity accompaning maturation can increase host exposure to parasites, or reproduction may decrease energy available to host immunologic defense. Ho wever, the present result indicates that maturation, and reproduction, is a ssociated with increased parasite abundance in A. piscinalis, an invertebra te host.