Behaviour 2019
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Hormones as mediators of animal personality: are we under-estimating hormone repeatability?
Kerry V Fanson1,2, Peter Biro1. 1Deakin University, Geelong, VIC, Australia; 2La Trobe University, Melbourne, VIC, Australia

Animal personality has become a major area of research, and there is increasing interest in understanding the underlying physiological mechanisms that shape these individual differences.   Hormones are one of the proposed mediators, but any mediator must also show within-individual consistency over time (i.e., repeatability). We conducted a comprehensive meta-analysis of hormone repeatability that included 1,132 estimates from 368 studies across three fields of study.  Overall mean repeatability was 0.58, but estimates differed substantially among study disciplines, being lowest in ecology/animal behavior (0.34), moderate in agriculture (0.52), and relatively high in medicine (0.68).  Hormone levels fluctuate constantly, so timing of hormone measurements is key.  Repeatability estimates were highest in species with the greatest knowledge about patterns of hormone expression, and thus the greatest ability to control the timing of hormone measurements.  These differences indicate that hormone repeatability may be higher than is often estimated in ecological/animal behavior studies, and that hormones may be a useful indicator of individual variation in behavior.