Contrasting effects of body condition on ectoparasite abundance in a social bat: different roles of season and host sex.

Understanding the interplay between host species ecology and parasite dynamics is crucial for comprehending disease transmission patterns, population structures, and ecosystem health. In most host-parasite systems, host body condition is of primary importance in ectoparasite host choice. Bats were considered an exception, as previously several studies suggested that bat ectoparasites showed no or minimal dependence on host body condition. We investigated the relationships between host condition and ectoparasite abundance in multiple populations of European bent-winged bats (Miniopterus schreibersii) and their arthropod ectoparasites (mites, nycteribiid bat flies and ixodid ticks). We found weak correlations between individual host condition and combined ectoparasite abundance, with seasonal fluctuations in both, and a single seasonal peak in parasite abundance. However, when treated individually, single ectoparasite groups showed contrasting answers to changes in body condition. Body condition had a significant positive effect on wing mite abundance and a significant negative effect on the prevalence and intensity of nycteribiid bat flies, overall with no effect on tick infestation. These responses moreover showed also seasonal differences, highly correlating with the life-stages of the two host's sexes. Our long-term, large-scale study of European bent-winged bats and their arthropod ectoparasites was able to detect major influences exerted by hosts' body condition on ectoparasites' host choice. Here we showed that bat populations undergo dynamic changes in their body condition during the active period of their annual cycle, with ectoparasites evolved to differentially exploit peaks or troughs of these changes.