Lizards in energy-saving mode: Urban individuals are smaller and have lower metabolic rates

Human-induced rapid environmental change is intensifying globally. Urbanization, a major form of human-induced rapid environmental change, alters ecosystems and exposes wildlife to urban stressors, including altered ambient temperatures and resource shifts. These alterations can impose selective pressures on wildlife, influencing behavior, physiology, and morphology. Alterations in resource availability and quality, and ambient temperature may be especially important for ectotherms, which depend on environmental conditions for regulating body temperature and activity. To date, little research has examined the physiological changes of ectotherms that are associated with urban life. In this study, we measured standard metabolic rate (SMR; N = 38) and recorded body mass and size in common wall lizards (Podarcis muralis) from an urban (N = 123) and a semi-natural habitat (N = 125) in Croatia. Our results show that urban lizards exhibit a lower SMR, reduced body mass, and shorter snout-vent length than their semi-natural counterparts. Despite these differences, body condition, assessed via the scaled mass index, did not vary between the two habitat types, potentially reflecting adaptive responses to urbanization-related environmental pressures. These findings suggest adaptive strategies of reptiles in urban environments and highlight the importance of studying both physiological and morphological traits to better understand the effects of urbanization on wildlife.