Ruthig_Gregory

Research Interests
I study the implications of the pathogen Saprolegnia on amphibian egg-laying behavior. Saprolegnia spp. is a ubiquitous aquatic Chromista, formally in the kingdom Fungi, which exists in almost all freshwater systems. While it had been noted anecdotally on amphibian eggs for years, work by Kiesecker and Blaustein brought to light some of its pathogenic capabilities on frogs in the Pacific Northwest of the United States. In my research I have isolated strains of Saprolegnia and inoculated eggs of two species of frogs in laboratory conditions. I have found that several strains of Saprolegnia can be pathogenic on bullfrog (Rana catesbeiana) and spring peepers (Pseudacris crucifer) in the southern Appalachian Mountains. I have also found seasonal changes in the incidence of the disease. My plans for the next breeding season are to examine susceptibility to infection and its relationship to several pertinent environmental conditions, including water temperature.

I am also interested in how infectious disease may affect the oviposition behavior of amphibian parents and consequently, the distribution of their offspring. At the Savannah River Site in South Carolina, I am examining seasonal changes in oviposition behavior as it relates to disease transmission. Several studies, including my own, suggest that large egg masses facilitate the spread of the disease. Southern leopard frogs (Rana sphenocephala) at the Savannah River Site have developed a social structure that may help them cope with this phenomenon. In colder months, many mating pairs aggregate and lay a large communal egg mass, which provides insulation for the eggs from cold temperatures. In the summer, however, the same frogs mate in isolated pairs and lay their eggs in individual masses. Since Saprolegnia is best able to grow and produce infective propagules in warmer conditions, I propose that the frogs alter their social behavior to limit disease transmission among their offspring. My hypothesis is that eggs laid communally will have higher Saprolegnia transmission and thus higher overall mortality in inoculated treatments, suggesting that seasonal change in the social behavior seen in Southern leopard frogs minimizes offspring infection. The results from this work will shed light on the selective pressures that infectious diseases have had on amphibian behavior, and on the potential effects of infectious disease on amphibian populations in the face of global climate change.