Community structure of Diplostomum spp. (Digenea: Diplostomidae) in eyes of fish: Main determinants and potential interspecific interactions

- Negative associations among genetically distinguished Diplostomum species
- Inter-annual variation in infracommunities surpassed inter-seasonal variation
- Decline in Diplostomum populations potentially caused by introduced fish species
- Infracommunity composition, structure not influenced by host ecology or phylogeny.
- Host length and age had significant effects on infracommunity structure.

Parasite communities in freshwater fish vary annually and seasonally and can be influenced by the length, age, sex and phylogeny of hosts, and by associations among parasite species. We assessed the influence of these factors in species of Diplostomum in the eyes of 828 fish in 20 different species collected in a single lake in early summer or autumn over a 5 year interval. Strong negative associations were found between five pairs of Diplostomum spp. and associations were strongest among abundant species. Most interspecific associations occurred among species inhabiting the lens, suggesting competitive interactions. However, the strongest association occurred between two Diplostomum spp. that inhabit different tissues (i.e., the vitreous humour and lens), indicating processes other than direct competition. Seasonal variation was small compared with inter-annual variation. Infection intensities were high in 2006 and decreased dramatically in 2010 and 2011. Infracommunity composition and structure showed no clear correspondence to the ecology or phylogeny of host species. Host length and age, but not sex, had significant effects on the structure of Diplostomum infracommunities in lenses. However, a significant amount of variance in lens infracommunities could not be explained, indicating the potential importance of other factors such as resistance or exposure in determining infracommunity structure.

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