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Abstract Urbanization that occurs across a gradient from low‐ to high‐density development, is a primary driver of landscape change that can affect biodiversity. Animals balance trade‐offs in obtaining resources and avoiding anthropogenic disturbances across the gradient of urbanization to maximize their fitness. However, additional research is necessary to understand seasonal variations in how animals respond to urbanization, particularly in arid regions, where resource availability shifts drastically across seasons. Our objective was to evaluate the response of a suite of bat species to urbanization and whether species shift their response to urbanization across seasons. We predicted that the response of bats to urbanization would differ among species, with some species being more sensitive to urbanization than others. We also predicted that bat species would increase the use of moderate and highly urbanized areas in the summer season where food and water resources were assumed to be greater compared with wildland areas. To evaluate these predictions, we used a stratified random sampling design to sample 50 sites with stationary acoustic bat monitors across the gradient of urbanization in the Phoenix metropolitan area, Arizona, USA during four seasons. We identified a total of 14 bat species during 1000 survey nights. Consistent with predictions, bat species exhibited different responses to urbanization, with most species exhibiting a negative relationship with urbanization, and some species exhibiting a quadratic or positive relationship with urbanization. Counter to predictions, most species did not appear to shift their response to urbanization across seasons. Consistent with predictions, plant productivity and water were important for some species in the summer season. Differences in the response of bat species to urbanization was likely related to species traits (e.g., wing morphology and echolocation call characteristics) and behavioral strategies that influence a species' sensitivity to anthropogenic disturbances and ability to access available resources in urbanized areas. Ultimately, to promote the management and conservation of bats, it is likely important to maintain resources in urbanized areas for bats that are more tolerant of urbanization and to conserve areas of undeveloped high‐quality habitat with low anthropogenic disturbance in wildland areas for bats that are sensitive to urbanization.

High viral tolerance coupled with an extraordinary regulation of the immune response makes bats a great model to study host-pathogen evolution. Although many immune-related gene gains and losses have been previously reported in bats, important gene families such as antimicrobial peptides (AMPs) remain understudied. We built an exhaustive bioinformatic pipeline targeting the major gene families of defensins and cathelicidins to explore AMP diversity and analyze their evolution and distribution across six bat families. A combination of manual and automated procedures identified 29 AMP families across queried species, with α-, β-defensins, and cathelicidins representing around 10% of AMP diversity. Gene duplications were inferred in both α-defensins, which were absent in five species, and three β-defensin gene subfamilies, but cathelicidins did not show significant shifts in gene family size and were absent in Anoura caudifer and the pteropodids. Based on lineage-specific gains and losses, we propose diet and diet-related microbiome evolution may determine the evolution of α- and β-defensins gene families and subfamilies. These results highlight the importance of building species-specific libraries for genome annotation in non-model organisms and shed light on possible drivers responsible for the rapid evolution of AMPs. By focusing on these understudied defenses, we provide a robust framework for explaining bat responses to pathogens.