Specialization of bat-fly interactions at different elevations in a montane forest of northern Peru

Hippoboscoidea flies exhibit highly specific ectoparasitic relationships with bats, shaped by both intrinsic factors (e.g. bat behaviour) and extrinsic factors (e.g. land use). Understanding the dynamics of these parasite-host interactions is essential for uncovering co-evolutionary patterns and informing conservation strategies. To this end, we studied bat-fly interactions across different elevations in a montane forest of Amazonas, northern Peru. The most abundant bats were <i>Carollia brevicauda, C. perspicillata</i> and <i>Sturnira oporaphilum</i>, while <i>Paraeuctenodes similis</i> and <i>Trichobius joblingi</i> were the most common flies. Most flies exhibited monoxenous host specificity. Bat-fly interaction networks revealed high modularity and specialization at both local and regional scales. Modules typically grouped bat species of the same genus or subfamily, suggesting that phylogenetic constraints and roosting behaviour may shape those interaction patterns. Nestedness within modules (compound structure) emerged in the aggregated regional network, aligning with the integrative hypothesis of specialization. Although network structures were broadly similar across sites, species turnover contributed to subtle differences in module composition and specialization. These differences were congruent with the changes in species roles of certain bats and flies. This study represents the first of its kind in Peru and addresses significant knowledge gaps in the ecology of bat-fly interactions in the Neotropics.