Anni Hämäläinen, Anja Guenther, Samantha C. Patrick, Wiebke Schuett

Pace-of-life syndromes (POLSs) are suites of life-history, physiological and behavioral traits that arise due to trade-offs between allocation to current and future reproduction. Traits generally show covariation that can arise from genetic and environmental influences on phenotypes and constrain the independent evolution of traits, resulting in fitness consequences and impacts on population dynamics. The notion that correlations among traits may vary among populations along environmental gradients suggests an important role for the environment in shaping and maintaining POLS. However, no synthesis has been attempted of the myriad ways in which environmental factors should influence POLS. Here, we formulate a series of hypotheses targeting the critical interfaces of the environment and life history-behaviour associations across different organisms. We discuss the hypotheses in light of findings from a systematic review of studies that measured changes in the association between behavior and life-history traits as a function of environmental conditions. The review revealed that POLS is often shaped by environmental variation, where harshness of the environment in early life has the most consistent effects on POLS. However, only partial or no effects of environmental variation were found in a number of studies, which may result from the highly variable study systems, traits, and environments studied. We highlight promising directions arising from the available studies and identify knowledge gaps that, if unaddressed, will impede progress in the field.