LAUSR

Abstract Parasitism is one of the most common strategies of resource exploitation in the planet, and the body size of the interacting species is a key factor to understanding the ecology and evolution of this trophic strategy. Here we report for the first time an unexpected interaction between a large nematode species of Eustrongylides (162 mm) and an adult female of the dwarf treefrog Dendropsophus nanus (28 mm). Species of Eustrongylides have complex life cycles, and their transmission occurs through a series of trophic interactions. The first intermediate hosts are oligochaetes, which can be ingested by several species of fish and, occasionally, by amphibians and reptiles. The parasite cycle is completed when these hosts are preyed on by birds. Anurans fill an important trophic position in terrestrial and aquatic ecosystems, acting as prey and predators for a wide variety of invertebrates and vertebrates. In this sense, parasites are good indicators of food web links, and the occurrence of a parasite in a host may reflect interactions between the host and its prey and predators. One intriguing fact we observed is the large size achieved by the parasite in a such a small host, since larger parasites tend to be associated with larger hosts that provide more relaxed niche constraints. Our finding raises many questions on the frequency and outcomes of such interactions, pointing to the critical influence of parasite transmission in food webs.