How do urban-dwelling bats cope with urbanisation? Sex-dependent plasticity of stress, microbiome and pathogen shedding

Understanding wildlifes stress and infection response patterns is crucial, especially for species like bats that are ecologically important and potential zoonotic reservoirs. While highly sensitive to habitat destruction and land use change, bats have shown adaptability in human-modified landscapes. This study investigates the impact of urbanisation on the endemic Reunion free-tailed bat (Mormopterus francoismoutoui), which roosts in a variety of rapidly urbanised habitats. We analysed 412 urine samples from 11 roosts across Reunion Island, covering a gradient of urban and agricultural land use. We measured urinary cortisol, microbiome diversity and the shedding of Leptospira bacteria and paramyxovirus. After accounting for natural cortisol level variations due to circadian rhythm, age, sex, reproduction and capture-induced stress, we found that bats roosting in agricultural and urban areas were in better condition and had lower cortisol levels, suggesting adaptation to human-modified landscapes. Less-stressed bats had more diverse urinary microbiomes and reduced pathogen shedding, suggesting that landscape modifications may indirectly alter the natural epidemiology of bat-borne infectious agents. These patterns were particularly pronounced in females, supporting sex-dependent plasticity to urbanisation in bats. Our study highlights how rapid urbanisation may elicit plastic responses in bats, with potential cascading effects on zoonotic risk of transmission.