Infectious diseases are poorly understood as selective forces on life history. Since the threat of disease is often heterogeneous in the environment, one would expect variation in traits that minimize the impact of diseases but are costly in their absence. This expectation can be tested in the host-pathogen system of the southern leopard frog, Rana utricularia and the aquatic, fungus-like chromista, Saprolegnia ferax. In the winter R. utricularia mating pairs lay large communal egg masses, while in the fall they lay their eggs in individual masses. The transmission of Saprolegnia, a pathogen of amphibian eggs, may be facilitated by warmer water. Separating egg masses may reduce Saprolegnia transmission in warmer months. This study will record the threat of infection and the type of egg-laying behavior of the frogs during both breeding seasons. A factorial experiment will test the importance of egg-laying behavior (single vs. communal) and disease (presence vs. absence) during both breeding seasons (fall vs. winter). This will be the first empirical study to examine the interaction between a pathogen and the environment and the effect of this interaction on a host.s life history. Understanding this interaction is particularly important in the face of global environmental change and worldwide amphibian extinctions.
