Explaining covariation between endo- and ecto-parasites in spreadwing damselflies (Zygoptera: Lestidae)

Abstract

Host individuals and populations are commonly infected by more than one type of parasite, yet studies examining parasite effects on host fitness often limit observations or experiments to only a single parasite taxon or to a narrow subset of potential parasite taxa. Addressing covariation between parasite taxa is important for determining the potential for misattributing effects caused by one parasite species to another parasite species, and also for testing more broadly whether host attributes relate to exposure or susceptibility to infection. In this study, parasitism by ectoparasitic water mites (Arrenuridae) and endoparasitic gregarines (Eugregarinidae) of two spreadwing damselfly species, Lestes disjunctus Selys, 1862 and Lestes forcipatus Rambur, 1842, was measured and analyzed for covariance. No significant correlations between the intensities of the two types of infecting parasites were found when both live and resisted mites were considered. However, significant negative correlations between live mites and gregarines were consistently found in L. forcipatus host samples, but never in L. disjunctus samples. These results show some species-specific patterns of covariation between mite and gregarine infections in damselflies. We propose potential underlying causes for this correlation related to parasite–host ecology and to changes in host behaviour resulting from water mite infection of L. forcipatus.