Temperature and the pace of life.

The pace-of-life syndrome (POLS) is a framework that attempts to explain empirically observed covariation between physiological, behavioral, and life history traits, whereby individuals fall along slow-fast and shy-bold continuums. The fundamental driver of the position of individuals along these trait axes is thought to be their metabolic rates, with high metabolism leading to faster growth, greater reproductive output, and bolder behavior. However, numerous exceptions to these patterns have been observed in nature, suggesting that crucial components are missing from the classical POLS framework. As many metabolic, physiological, and life history traits are temperature dependent, a growing number of studies have begun to test the role played by the thermal physiology of individuals and the thermal environments in which they live in mediating the trait relationships within POLS. These studies have led to an expansion of classical POLS into what has been called "extended POLS." Here, we review the recent literature on extended POLS and identify the major themes and patterns that are emerging in this nascent field. We further identify gaps and key outstanding questions in how temperature may drive or modify classical POLS. Finally, we address issues with how temperature and POLS are integrated in empirical studies and suggest pathways by which progress can be made towards a cohesive understanding of the physiology-behavior-life history nexus. Significance statement: The pace of life syndrome (POLS) is an integrative framework that links life-history, behavioral, and physiological traits into covarying axes that are structured by metabolism. Recent studies have provided only mixed support for the original POLS hypothesis and instead have highlighted the potential importance of thermal physiology in explaining patterns of trait covariation. We review this nascent literature and argue that environmental temperature, the thermal sensitivity of traits, and acclimation to thermal environments can influence the presence and/or direction of trait covariations within individuals or populations. Though some patterns have emerged in the recent POLS literature, important remaining gaps are slowing progress in this field. We suggest avenues by which future investigations can test the proximate and ultimate mechanisms underlying trait covariation in wild animal populations. [ABSTRACT FROM AUTHOR]