Seasonal Turnover in Bat Skin Mycobiota: Contrasting Fungal Communities Between Hibernation and Reproduction in Greater Mouse-Eared Bats (Myotis myotis)

The skin of bats hosts diverse microbial communities, yet most research has focused on bacteria or single fungal pathogens such as <i>Pseudogymnoascus destructans</i>. Here, we present the first direct comparison of culturable skin mycobiota in the greater mouse-eared bat (<i>Myotis myotis</i>) between hibernation and the reproductive season. Swabs collected from hibernating bats in the Nietoperek reserve and from maternity colonies in Lipy yielded 41 fungal species, including 27 that represent new records for <i>M. myotis</i>. Winter assemblages were less diverse but strongly dominated by <i>Penicillium</i> (>90% of isolates), while summer maternity roosts supported broader communities shaped by environmental exposure and plant-associated fungi. Despite seasonal turnover, a small set of taxa, including <i>Aspergillus fumigatus</i>, <i>Mucor fragilis</i>, and <i>Pseudogymnoascus pannorum</i>, persisted across both seasons, indicating the presence of a limited core mycobiota. Richness was higher on wing membranes than on tail membranes, whereas biometric variables such as sex, age, body mass, and forearm length showed only weak and inconsistent associations with fungal diversity. These findings demonstrate that seasonal filtering is likely one of the main factors determining the skin mycobiota in <i>M. myotis</i>. Additionally, we expand the known fungal diversity of this species, and emphasize its role as a reservoir of environmental, opportunistic, and pathogenic fungi.