Introduced Urban Lizards (Podarcis muralis) Exhibit Plastic Activity Patterns and Precise Behavioral Thermoregulation

AbstractEffective thermoregulation is important for most ectotherms, as body temperature determines the rate of nearly all physiological processes. However, for most organisms, we lack an understanding of which environmental factors affect thermoregulatory behaviors, especially outside of a laboratory setting and over an entire day. Introduced populations of the common wall lizard (Podarcis muralis) in Cincinnati, Ohio, are thriving after an introduction almost 75 years ago. To noninvasively quantify daily thermoregulatory behaviors and thermoregulatory effectiveness, we used infrared thermography (a thermal imaging camera) to conduct repeated standardized sampling every 30 min across the lizard's normal activity period (0800-2000 hours) at multiple urban locations. We also measured air temperature, ultraviolet (UV) radiation, and wind speed, while 3D-printed operative temperature models quantified available temperatures throughout the activity period. Lizard activity varied throughout the day and peaked in the early afternoon. Furthermore, activity patterns were associated with the interaction of temperature and UV radiation intensity, such that predicted activity is greatest at high temperatures when UV is low and at low temperatures when UV is high. Activity was limited by cool environmental temperatures, even on hot days in midsummer. When lizards were active, they thermoregulated precisely and achieved body temperatures closely matching preferred temperatures selected in a laboratory gradient in a previous study. Furthermore, field body temperatures did not vary because of sex, reproductive status, or size. Data on daily activity and thermoregulatory decision-making, especially in an urban habitat, provide valuable insight into how an ectothermic organism integrates multivariate sensory inputs from the environment to make behavioral decisions. The role of environmental conditions in behavioral decision-making is especially relevant in predicting geographical range expansions, particularly in the context of changing urban environments and introduced species.