Hitchhiking Parasites: Unstructured Populations of Bat Ectoparasites Reveal Host-Driven Dispersal

Understanding factors influencing the dynamics and distribution of parasites is essential to decipher the mechanism behind their spread and the identification of populations with elevated risks of infection. Bats-together with the diverse parasites they host and the influence of their social behaviour on parasitism-offer a suitable system. We investigated the extent to which differences in life history traits between parasite species found on the same host influence their dispersal dynamics across bat metapopulations. To do so, we compared the population genetic structure of two obligate ectoparasites of the same bat, the Daubenton's bat (Myotis daubentonii): the specialist wing mite Spinturnix andegavinus and the more generalist bat fly Nycteribia kolenatii, and we expected the bat fly to exhibit a higher connectivity than the wing mites. Using double-digest restriction site-associated DNA sequencing (ddRADseq), we genotyped 426 bat flies and 171 wing mites across 13 maternity colonies and foraging sites and 1 putative swarming site in Switzerland. We found high genetic homogeneity across the metapopulations for both species, highlighting the dispersal capacity of N. kolenatii and S. andegavinus, probably driven by the high mobility of their bat hosts. The positive population-specific F_IS and the excess of low-frequency alleles in both species suggest within-site expansion and provide insights into the life cycle of these ectoparasites. Altogether, these findings enhance our understanding of the interplay between nycteribiid flies and spinturnicid mites and their host movement in shaping population structure in Europe, offering broader insights into their potential role in pathogen transmission across bat populations.