Host phenologies and the life history of horsehair worms (Nematomorpha, Gordiida) in a mountain stream in northern Japan

Abstract

AbstractThe occurrence of many parasites and their hosts vary conspicuously by season due to their periodic life history events. Nematomorphs are common parasites in terrestrial‐aquatic ecotones, but it is still unknown how the nematomorphs complete their complex life cycles by using multiple hosts that are potentially seasonally variable. In this study, we examined the life history of a nematomorph (Gordionus sp.) inhabiting a mountain stream in northern Japan by the seasonal survey of their infection on aquatic and terrestrial hosts and laboratory experiments. Adults of Gordionus sp. entered into stream from early June to mid‐July. The laboratory experiment suggested that the newly hatched larvae become infective to intermediate host (aquatic insect larvae) from September to November, depending on the water temperature. The nematomorph larvae infected aquatic insect hosts with diverse emergence phenology, which result in prolonged temporal window for the trophic transmission between aquatic and terrestrial hosts. The common definitive host (Pterostichus thunbergi) seemed to survive multiple years, which would allow the nematomorph larvae to fully develop within the infected host. Trophically transmitted parasites sometimes track a specific pathway of prey–predator interactions within a food web and thus are sensitive to temporal match–mismatch between intermediate and definitive hosts. Contrary to this, the nematomorphs we studied may benefit from using temporally diverse pathways across aquatic and terrestrial food webs, which may result in maintaining the populations in their seasonal environment.