Patterns ofClinostomum marginatuminfection in fishes and amphibians: integration of field, genetic, and experimental approaches

Abstract

AbstractDigenetic trematodes of the genusClinostomumare cosmopolitan parasites infecting fishes, amphibians, reptiles, and snails as intermediate hosts. Despite the broad geographical distribution of this genus, debate about the number of species and how they vary in host use has persisted. To better understand patterns of infection among host species and across life stages, we used large-scale field surveys and molecular tools to examine five species of amphibians and seven species of fishes from 125 California ponds. Among the 12,360 examined hosts, infection was rare, with an overall prevalence of 1.7% in amphibians and 9.2% in fishes. Molecular evidence indicated that both groups were infected withClinostomum marginatum. Using generalized linear mixed effects models, host species identity and host life stage had a strong influence on infection status, such thatLepomis cyanellus(green sunfish) (49.3%) andTaricha granulosa(rough skinned newt) (9.2%) supported the highest overall prevalence values, whereas adult amphibians tended to have a higher prevalence of infection relative to juveniles (13.3% and 2.5%, respectively). Experimentally, we tested the susceptibility of two amphibian hosts (Pseudacris regilla[Pacific chorus frog] andAnaxyrus boreas[western toad]) to varying levels of cercariae exposure and measured metacercariae growth over time.Pseudacris regillawas 1.3× more susceptible to infection, while infection success increased with cercariae exposure dose for both species. On average, metacarcariae size increased by 650% over 20 days. Our study highlights the importance of integrating field surveys, genetic tools, and experimental approaches to better understand the ecology of host–parasite interactions.