Bat phylogeny and geographic location, rather than bat individual characteristics, explains the pattern of trypanosome infection in Europe.

Understanding the drivers of parasite susceptibility provides valuable information, such as how parasites spread, what conditions favour their transmission, and what host characteristics make infections more likely. It can also reveal co-evolutionary dynamics and adaptation strategies between hosts and parasites. In this study, we investigated the infection patterns of several bat species across Europe by trypanosome parasites. We used phylogenetic generalised linear mixed models to investigate whether geographic location, individual characteristics (sex, body mass and body size) or species affect trypanosome infection. Additionally, we examined whether infection patterns were influenced by host phylogeny (similar prevalence among genetically close species) and tested for a cophylogenetic signal between bats and trypanosomes. Our results show that individual characteristics were poor predictors of trypanosome infection, whereas host phylogeny and geographic location significantly explained variation in infection. We also found a cophylogenetic congruence between bat species and trypanosome lineages, but this was primarily driven by the association between the bent-winged bat (Miniopterus schreibersii) and its trypanosome lineages. Overall, host phylogeny emerges as the main determinant of trypanosome infection in bats. These findings suggest that the probability of infection is governed by deterministic factors rather than random encounters between bats and their trypanosome parasites. However, the high host specificity and absence of a strong cophylogenetic signal indicate that random host switching, rather than co-speciation, is the dominant mechanism shaping bat-trypanosome associations.