Thermal physiology: a new dimension of the pace-of-life syndrome

1) Current syndrome research focuses primarily on behavior with few incorporating components of physiology. One such syndrome is the Pace-of-Life Syndrome (POLS) which describes covariation between behaviour, metabolism immunity, hormonal response, and life history traits. Despite the strong effect temperature has on behavior, thermal physiology has yet to be considered within this syndrome framework. 2) We proposed the POLS to be extended to include a new dimension, the cold-hot axis. Under this premise, it is predicted that thermal physiology and behavior would covary whereby individual positioning along the thermal continuum would coincide with that of the behavioral continuum. 3) This hypothesis was tested by measuring thermal traits of delicate skinks (Lampropholis delicata) and linking it to their behavior. Principal components analysis and structural equation modelling were used to determine if traits were structured within the Pace-of-Life Syndrome (POLS) and to characterize the direction of their interactions. 4) Model results supported the inclusion of the cold-hot axis into the POLS and indicated that thermal physiology was the driver of this relationship, in that thermal traits either constrained or promoted activity, exploration, boldness, and social behavior. 5) This study highlights the need to integrate thermal physiology within a syndrome framework.