GURALNICK, Robert P; University of Colorado: A COMPARATIVE APPROACH TO UNDERSTANDING CAUSES AND CONSEQUENCES OF MOLLUSC-DIGENEAN SIZE RELATIONSHIPS: A CASE STUDY WITH ALLOCREADIID TREMATODES AND CYCLOCALYX CLAMS

Allocreadiid flukes often parasitize and castrate sphaeriid freshwater clams. The effects of parasitic castrators on host population life history can lead to earlier reproductive onset, changes in body size, or changes in the number of reproductive events per yr. However, little is known about whether species or clade-level traits are associated with parasite prevalence. Here I examine if phenotypic effects, e.g., size change, seen at the population level sort to the species or clade level. To answer this question, I determined if different sized host species in the ecologically important, widespread and common freshwater clam subgenus Cyclocalyx have different prevalences of allocreadiid infection. After showing that large species are over 12 times more likely to have patent infections than small species, I generated a hypothesis for the evolution of size within Cyclocalyx lineages. Transitions from large size to small or vice versa have occurred at least twice and probably many times during lineage diversification, perhaps relating to trade-offs between clutch size and parasite risk. Finally, based on existing life history data, I show that it is unlikely that age and body size are correlated and, therefore, a simple age-exposure model is not a sufficient explanation for parasite prevalence in this clade.