Consequences of parasitism to marine invertebrates: Host evolution?

Abstract

Parasitism among aquatic invertebrates is common, if not ubiquitous, and can be pathological to hosts. However, host evolution in response to parasitism has received little attention, particularly for marine invertebrates. Drawing on the rich literature demonstrating prey adaptations to predators, I develop analogous predictions for the ways in which host life histories may be molded by their parasites. Such adaptations are expected when the effects of parasites are severe and when the probability of infection is high. Predicted life history changes include the evolution of semelparity, reduced age at first reproduction and reduced size at first reproduction. Using Recent and fossil populations of two bivalves species in the genusTransennella, I show that the incidence of trematode parasites may explain a trend of reduced size through time and contribute to the maintenance of sexual dimorphism for size. © 1991 by the American Society of Zoologists.