Routine metabolic rate is not associated with boldness in zebrafish

Consistent individual differences in behavior are prevalent throughout the animal kingdom and are thought to be important contributors to evolutionary adaptation. However, the biological basis for individual differences are poorly understood. One explanatory framework that has gained traction is the pace of life syndrome (POLS) hypothesis. The POLS hypothesis proposes that behavioral variation arises from variation in basic physiological functions like metabolism. In particular, the POLS predicts that individuals with higher baseline metabolic demands will be more willing to take risks to attain the requisite resources. To date, support for this hypothesis when applied within species has been mixed, leading to the tentative conclusion that the relationship between metabolism and behavior depends on factors like species, sex, and context. We sought to determine if the POLS hypothesis held in zebrafish, a widely used model organism with well-developed genetic and neurobiological tools that would allow us to better understand how biological and environmental factors influence predictions of the POLS hypothesis. We tested the POLS hypothesis in adult zebrafish by measuring the relationship between routine metabolic rate, as assessed by oxygen consumption, and exploration of a novel tank. We found no clear relationship between boldness-related behaviors in the novel tank and metabolism in female or male zebrafish of the TU or WIK strains. Our findings suggest that a key prediction of the POLS hypothesis does not hold in zebrafish.