Establishment and interspecific associations in two species of Ichthyocotylurus (Trematoda) parasites in perch (Perca fluviatilis).

Anna Faltýnková,E Tellervo Valtonen,Anssi Karvonen

doi:10.1186/1756-3305-4-85

Abstract

BackgroundCo-infections of multiple parasite species in hosts may lead to interspecific associations and subsequently shape the structure of a parasite community. However, few studies have focused on these associations in highly abundant parasite species or, in particular, investigated how the associations develop with time in hosts exposed to co-infecting parasite species for the first time. We investigated metacercarial establishment and interspecific associations in the trematodes Ichthyocotylurus variegatus and I. pileatus co-infecting three age cohorts of young perch (Perca fluviatilis).ResultsWe found that the timing of transmission of the two Ichthyocotylurus species was very similar, but they showed differences in metacercarial development essentially so that the metacercariae of I. pileatus became encapsulated faster. Correlations between the abundances of the species were significantly positive after the first summer of host life and also within the main site of infection, the swim bladder. High or low abundances of both parasite species were also more frequent in the same host individuals than expected by chance, independently of host age or size. However, the highest abundances of the species were nevertheless observed in different host individuals and this pattern was consistent in all age cohorts.ConclusionsThe results suggest similar temporal patterns of transmission, non-random establishment, and facilitative rather than competitive associations between the parasite species independently of the age of the infracommunities. However, we suggest that spatial differences in exposure are most likely responsible for the segregation of the parasite species observed in the few most heavily infected hosts. Regardless of the underlying mechanism, the result suggests that between-species associations should be interpreted with caution along with detailed examination of the parasite distribution among host individuals.

Highlights

Co-infections of multiple parasite species in hosts may lead to interspecific associations and subsequently shape the structure of a parasite community
We investigated the establishment and interspecific associations of two trematode species, Ichthyocotylurus pileatus and I. variegatus, coinfecting young age cohorts of their second intermediate host, perch (Perca fluviatilis)
Parasite establishment in fish First metacercariae were detected in 0+ fish in July after which the prevalences of both parasite species increased steadily, reaching 100% for I. pileatus in September and 81.8% for I. variegatus in October (Table 1)

Summary

Introduction

Co-infections of multiple parasite species in hosts may lead to interspecific associations and subsequently shape the structure of a parasite community. Co-infections, i.e. infections of hosts by multiple parasite species are the rule in host-parasite interactions in nature [1,2,3,4] These infections may lead to different types of intraspecific and interspecific associations, which may shape the structure of a parasite community (reviewed in [5]). Dynamics of co-infections in these species are not well known, but form an interesting area of research as high infection intensities of these species could lead to a range of interspecific and intraspecific associations within the hosts. This would be likely in species-pairs infecting the same host organs. Very little is known about the dynamics of development and encapsulation in these parasites, especially in systems where two species co-infect the host at the same time

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