Clara Castex

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.

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.

After its near eradication in the 1940s, the common bed bug (Cimex lectularius) experienced a global resurgence. Within a few years after, some populations displayed insecticide resistance. Two distinct lineages of bed bugs were identified, each associated with humans and bats, respectively. A strong genetic differentiation was identified between bugs from human and bat sites across Europe. This raises the question of whether the same pattern is found at a local scale. Moreover, because long-distance dispersal of bed bugs is essentially human-mediated, we investigated the spread of bed bugs within and among sites. Using mitochondrial (cytochrome oxidase unit I (COI) and 16S rRNA genes) and nuclear (10 microsatellite loci) markers, we compared the genetic composition of human- and bat-associated bed bugs from western Switzerland. We first conducted a median-joining analysis and compared it to European sequences to detect local-scale host-specific separation of haplotypes. We estimated levels of genetic diversity and structure between and within the two host-associated bed bugs. Our results reveal two genetic clusters associated with bats and humans and a strong structure among human sites (F_SC = 0·579). An analysis of knock-down insecticide resistance gene variants (V419L, L925I, I936F) shows that bed bugs infecting humans in western Switzerland carry insecticide resistance (99%) whereas bed bugs infecting bats do not (0%). Our results show that at the scale of western Switzerland, bed bugs are structured by host association, thus supporting the hypothesis of host specialization in the common bed bugs. Moreover, human-associated bugs might have settled from multiple colonization events and/or undergone bottlenecks.

Background After its nearly eradication in the 1940’s, the bed bug (Cimex lectularius) experienced a global resurgence with some populations displaying insecticide resistance. Two distinct lineages of bed bugs have been identified, one of which is associated with humans and the other with bats. Given that bat roosts can be shared within human shelters, investigating host specialisation in bed bugs is essential to gain a better understanding of the potential risks of cross-species transmission. Methods We analysed and compared the genetic composition of human and bat-associated bed bugs. We first conducted a median-joining analysis based on COI and 16S rRNA mitochondrial genes to detect any host-specific separation of haplotypes. Then, using 10 microsatellites, we estimated the genetic diversity and structure between and within the two hosts-associated bed bugs. Finally, we carried out an analysis of knock-down insecticide resistance gene variants to assess the difference in resistance of the host-associated common bed bugs to pyrethroid insecticides. Results The median-joining analysis shows a clear separation of all haplotypes that are host-specific. Consistently, the analysis of genetic structure reveals two genetic clusters associated with bats and humans with some structure among human-associated sites. Human-associated bed bugs might have settled from multiple colonisation events or undergone bottlenecks. This separation is also supported by the analysis of knock-down insecticide resistance gene variants which shows that bed bugs infecting humans have evolved insecticide resistance in contrast to the ones infecting bats. Conclusion Taken together, our results show that bed bugs seem to have evolved into genetically differentiated lineages specialised on different hosts, thus supporting the hypothesis of host specialisation in the common bed bugs.