Helminth Community in the Llanos Frog, Lepidobatrachus llanensis (Ceratophryidae), from the Dry Chaco

Abstract. The present study predicts that helminth community diversity and parasite transmission are influenced by host behavior and its habitat. This prediction was tested by analyzing for the first time the helminth community of Lepidobatrachus llanensis, an aquatic species that inhabits exclusively ephemeral water bodies in the Dry Chaco ecoregion. In the drought periods, L. llanensis burrows underground and forms a cocoon to minimize water loss, emerging again in the rainy season (e.g., in summer months). A total of 21 frogs was examined for parasites. Parasite community structure was analyzed using helminth parasite richness, diversity, and abundance. The helminth community of this frog consisted of 17 species, composed mostly of platyhelminth species (76%), followed by nematodes (24%). Ophiotaenia sp. was most prevalent (71%, confidence interval [CI]: 51.4–90.6%), followed by Choledocystus elegans (57%, CI: 35.8–78.2%). Infected frogs harbored a maximum of seven helminth species. At the infracommunity level, the mean species richness was 4.24 ± 1.79 per infected frog. Parasites were found in all major organs, with highest prevalence in the body cavity. Helminth species showed a typical aggregated pattern of distribution with unequal abundances. Parasite transmission to the frog host occurs by oral ingestion and skin penetration. As predicted, we found that the composition of the parasite community of this aquatic frog included multiple helminths, including parasitic species characteristic of both aquatic and terrestrial life cycles, with greater occurrence of trematodes that likely benefit from seasonal host aggregation during the rainy period associated with their reproductive strategies and by environmental factors such as seasonal dwelling in dry soil. This behavior in an otherwise aquatic frog enables infections by nematodes (L3) with a terrestrial life cycle absent from other aquatic frogs from South America.