Abstract

Mounting empirical evidence links environmental disturbance with changes in parasitism. Agricultural run-off in wetland habitats and surrounding land use can greatly impact parasite acquisition by affecting hosts or the parasites themselves. Thus, the aim of this thesis was to determine if agricultural impacts were detectable in the parasite communities of frogs. Parasite communities of metamorphic Rana pipiens from five reference wetlands and four wetlands receiving agricultural run-off in Quebec's St. Lawrence River basin were examined in 2004 and 2005. Parc Le Rocher, a reference wetland within a managed park, and Rivière Chibouet, an agricultural wetland with heavy pesticide contamination, differed from the other wetlands perhaps because of surrounding agriculture. The component and infracommunities in frogs from these wetlands were characterised by low species richness and diversity. Spearman-rank correlations and a multivariate analysis revealed that the landscape variables, particularly agricultural area, surrounding the wetland, and concentrations of dissolved organic carbon were positively related to parasite community structure. Landscape effects may hinder parasite transmission by limiting the access of definitive hosts to particular wetlands. Echinostoma sp. was the only parasite found at all localities in both years of collection. Abundance of this parasite was positively associated with agricultural area, as well as with Parc Le Rocher and Rivière Chibouet, suggesting that generalist parasites persist in impacted environments compared to more host-specific species. At Rivière Chibouet, pesticide contamination may have contributed to reduced parasitism, possibly through negative effects on intermediate hosts and free-living stages. This study suggests that the parasite communities of leopard frogs reflect environmental disturbance, and may be appropriate sentinel organisms for the ecological condition of wetland habitats