Urbanization has triggered the widespread phenomena termed the heat island effect, leading to constantly elevated temperatures in built environments. This effect profoundly impacts ectothermic species, whose physiological and behavioral performance are inevitably affected by thermal environment. Some animals, including reptiles, have shown increased thermal tolerance and bolder behaviors in urban areas, suggesting adaptive change to urban environment. According to the extended pace-of-life-syndrome (POLS) hypothesis, these alter thermal regimes, mediated by shifts in metabolism, thereby shifting the balance along a shy-bold behavioral continuum.
Although urbanization has been shown to induce trait changes consistent with the hypothesis in some ectotherms, evidence directly linking urbanization and the extended POLS hypothesis remains limited. This study investigated whether urbanization drives integrated shifts in multiple traits within the extended POLS framework using the Japanese five-lined skink (Plestiodon japonicus). This ectothermic species acts as an ideal model as it is found in abundance in both urban and sub-urban sites. Under this framework, urban skinks were predicted to exhibit a syndrome characterized by heightened activity, greater exploration, increased risk-taking, and higher thermal preferences suited for hotter habitats. Lizards were collected from both urban and sub-urban sites, and three behavioral assays were conducted to quantify individual variation in three behavioral traits: activity, exploratory tendency, and boldness. Additionally, a thermal preference assay was conducted to evaluate thermal physiological differences between the two populations. We also evaluated the consistency of each trait.
Results showed no significant difference in thermal preference between populations. However, in contrary to predictions based on the hypothesis and most recent findings, the sub-urban population showed significantly higher activity, boldness, and exploratory tendency than the urban population. Further analysis showed the behavioral traits were strongly inter-correlated, forming a distinct syndrome. In contrast, the behavioral traits generally showed no correlation with thermal traits, with the exception of a potential functional link between exploratory tendency and accuracy of thermoregulation. The findings offer partial support for the extended POLS hypothesis. Our results suggest that the influence of urbanization on ectotherm traits is highly context-dependent and influenced by specific environmental conditions, rather than consistently aligning with the hypothesis.