Alternative life cycle strategies and colonization of young anurans by Gorgoderina attenuata in Nebraska

Studies on life cycles and epizootiology of North American frog bladder flukes indicate that adult frogs become infected predominantly by ingesting tadpoles or other frogs that serve as second intermediate hosts for gorgoderid metacercariae. Other studies have indicated that newly metamorphosed frogs are rarely infected with these parasites because they are gape-limited predators that cannot feed on large intermediate hosts such as tadpoles and other frogs. We examined the role of potential intermediate hosts in the recruitment of the frog bladder fluke, Gorgoderina attenuata, to metamorphosed northern leopard frogs, Woodhouse's toads, and bullfrogs from western Nebraska. We completed the life cycle of G. attenuata in the laboratory in 3 anuran species by experimentally infecting a variety of hosts. In addition, we generated and compared DNA sequence data from life cycle stages collected from a variety of naturally infected hosts. Our field and laboratory data indicate that in Nebraska G. attenuata has a truncated, 2-host life cycle that includes fingernail clams and anurans. Cercariae are ingested directly by tadpoles; unencysted juvenile worms then develop in the kidneys of tadpoles before moving to, and maturing in, the urinary bladder when tadpoles metamorphose. Additionally, G. attenuata can infect metamorphosed leopard frogs, bullfrogs, and toads when metacercariae in damselfly second intermediate hosts are ingested. These worms can also infect adult bullfrogs when they feed on other infected anurans possessing worms in their kidneys. Comparison of our material to published accounts of G. attenuata morphology and life cycles in Massachusetts suggests that previous work may have inadvertently involved 2 different species of gorgoderids. Our comparative approach to life cycle studies in different anuran life stages and multiple species of hosts suggests that tadpoles and metamorphosed anurans have favored alternative life cycle strategies in this trematode.