Effects of density and linoleic acid exposure on the chemical profiles of cercarial echinostome parasites

Abstract

For many 2- and 3-host life cycle trematode parasites, transmission between hosts requires the cercarial stage to emerge from the first intermediate host to infect a second intermediate host or a definitive host. As the role of chemicals in cercarial-host interactions has only been investigated in a few trematode species and in limited contexts, it is unclear if ecological factors affect the diversity of types and concentration of emissions. I investigated the influence of cercarial density and host exposure to linoleic acid on the oxylipin emissions of the trematode parasite, Echinostoma trivolvis lineage c. Using high performance liquid chromatography-tandem mass spectrometry, a total of 40 oxylipins were quantified from nine samples ranging from 363-1621 cercariae per 10 mL, with seven oxylipins being present in ≥75% of the samples. Neither the diversity of types of oxylipins nor their concentrations showed a monotonic relationship with cercarial density, and no linear trends were observed. Forty-seven oxylipins were quantified from four samples of cercariae that each originated from infected snails that were exposed or unexposed to linoleic acid (385-674 cercariae/10 mL and 470-640 cercariae/10 mL, respectively), with 29 oxylipins being quantified in ≥75% of the samples in the unexposed, exposed, or both groups. Among these, oxylipin concentrations between the groups did not differ. Although linoleic acid appeared to be higher in the tissues of exposed snails, this increase did not affect the chemical profiles of the cercariae themselves. My thesis is the first to demonstrate that cercariae of E. trivolvis lineage c emit oxylipins. In addition, this work is the first to test whether density and host diet influence the chemical emissions of echinostome cercariae. By understanding how ecological factors may influence oxylipin emissions of parasites, we can better understand how these chemicals shape patterns of infection, host-parasite dynamics, and ecosystem-level interactions.