Populations of the damselflyCoenagrion hastulatumat the edge of the species range have fewer gregarine and water mite parasites

Abstract

SummaryThe metapopulation theory predicts that the more distant a host population is from other populations, the more challenged will be a parasite to colonise it. We studied parasite prevalence of two parasite taxa across the geographical range of their host in Finland, from more dense host population structure in the south of Finland, towards the northern edge of the host distribution characterised by more isolated populations.We found that prevalence of both water mites and gregarines decreased with increasing latitude towards the distribution edge with more isolated population structure of the host damselfly,Coenagrion hastulatum. Furthermore, the prevalences of the two parasite groups were positively correlated.The results are discussed in the context of three non‐mutually exclusive hypotheses, explaining why host species have fewer parasites at the edge of their geographic range: (i) unsuitable host hypothesis, (ii) physiological barrier hypothesis and (iii) metapopulation hypothesis.