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Thermoregulatory decisions impact nearly every aspect of the physiology, performance, and ecology of ectotherms. Thus, understanding the factors which influence ectotherm thermoregulatory behaviors across ecological contexts and environmental conditions is essential in predicting responses to novel or changing environments. Specifically, quantifying such behaviors across the entire diel cycle – day and night – is key to understanding the impact on physiological processes that happen during periods of inactivity, such as digestion. Utilizing high-resolution time-series data, we quantified the diel cycle of thermoregulatory behaviors in fed and unfed common wall lizards (Podarcis muralis) over five consecutives days. We first tested the hypothesis that feeding status affects diurnal and nocturnal thermoregulation. Second, we quantified the impact of feeding status on patterns of consistency and correlation within and among individuals in diurnal and nocturnal thermoregulatory behaviors. Lizards modulated their behavior in response to feeding status, conserving energy by choosing lower temperatures when unfed and by seeking higher temperatures when fed. We observed consistent among-individual differences (repeatability) in thermoregulatory behaviors across diurnal and nocturnal periods. Furthermore, diurnal and nocturnal thermoregulatory behaviors were positively correlated within individuals. We demonstrate that this diurnal ectotherm actively thermoregulates during the night, a finding particularly pertinent in urban environments, where artificial light and heat can prolong the active period of lizards. Overall, this research provides valuable insight into the flexible thermoregulation strategies of a species highly successful in expanding its range, demonstrating the importance of considering both diurnal and nocturnal activity. 

Abstract Thermoregulatory decisions impact nearly every aspect of the physiology, performance, and ecology of ectotherms. Thus, understanding the factors which influence ectotherm thermoregulatory behaviors across ecological contexts and environmental conditions is essential in predicting responses to novel or changing environments. Specifically, quantifying such behaviors across the entire diel cycle—day and night—is key to understanding the impact on physiological processes that happen during periods of inactivity, such as digestion. Utilizing high-resolution time-series data, we quantified the diel cycle of thermoregulatory behaviors in fed and unfed common wall lizards (Podarcis muralis) over five consecutives days. We first tested the hypothesis that feeding status affects diurnal and nocturnal thermoregulation. Second, we quantified the impact of feeding status on patterns of consistency and correlation within and among individuals in diurnal and nocturnal thermoregulatory behaviors. Lizards modulated their behavior in response to feeding status, conserving energy by choosing lower temperatures when unfed and by seeking higher temperatures when fed. We observed consistent among-individual differences (repeatability) in thermoregulatory behaviors across diurnal and nocturnal periods. Furthermore, diurnal and nocturnal thermoregulatory behaviors were positively correlated within individuals. We demonstrate that this diurnal ectotherm actively thermoregulates during the night, a finding particularly pertinent in urban environments, where artificial light and heat can prolong the active period of lizards. Overall, this research provides valuable insight into the flexible thermoregulation strategies of a species highly successful in expanding its range, demonstrating the importance of considering both diurnal and nocturnal activity. 

Aging is the price to pay for acquiring and processing energy through cellular activity and life history productivity. Climate warming can exacerbate the inherent pace of aging, as illustrated by a faster erosion of protective telomere DNA sequences. This biomarker integrates individual pace of life and parental effects through the germline, but whether intra- and intergenerational telomere dynamics underlies population trends remains an open question. Here, we investigated the covariation between life history, telomere length (TL), and extinction risk among three age classes in a cold-adapted ectotherm ( Zootoca vivipara ) facing warming-induced extirpations in its distribution limits. TL followed the same threshold relationships with population extinction risk at birth, maturity, and adulthood, suggesting intergenerational accumulation of accelerated aging rate in declining populations. In dwindling populations, most neonates inherited already short telomeres, suggesting they were born physiologically old and unlikely to reach recruitment. At adulthood, TL further explained females’ reproductive performance, switching from an index of individual quality in stable populations to a biomarker of reproductive costs in those close to extirpation. We compiled these results to propose the aging loop hypothesis and conceptualize how climate-driven telomere shortening in ectotherms may accumulate across generations and generate tipping points before local extirpation.