Data from: How integrated are behavioural and endocrine stress response traits? A repeated measures approach to testing the stress coping style model

It is widely expected that physiological and behavioral stress responses
will be integrated within divergent stress-coping styles (SCS) and that
these may represent opposite ends of a continuously varying
reactive–proactive axis. If such a model is valid, then stress response
traits should be repeatable and physiological and behavioral responses
should also change in an integrated manner along a major axis of
among-individual variation. While there is some evidence of association
between endocrine and behavioral stress response traits, few studies
incorporate repeated observations of both. To test this model, we use a
multivariate, repeated measures approach in a captive-bred population of
Xiphophorus birchmanni. We quantify among-individual variation in
behavioral stress response to an open field trial (OFT) with simulated
predator attack (SPA) and measure waterborne steroid hormone levels
(cortisol, 11-ketotestosterone) before and after exposure. Under the mild
stress stimulus (OFT), (multivariate) behavioral variation among
individuals was consistent with a strong axis of personality (shy–bold) or
coping style (reactive–proactive) variation. However, behavioral responses
to a moderate stressor (SPA) were less repeatable, and robust statistical
support for repeatable endocrine state over the full sampling period was
limited to 11-ketotestosterone. Although post hoc analysis suggested
cortisol expression was repeatable over short time periods, qualitative
relationships between behavior and glucocorticoid levels were counter to
our a priori expectations. Thus, while our results clearly show
among-individual differences in behavioral and endocrine traits associated
with stress response, the correlation structure between these is not
consistent with a simple proactive–reactive axis of integrated
stress-coping style. Additionally, the low repeatability of cortisol
suggests caution is warranted if single observations (or indeed repeat
measures over short sampling periods) of glucocorticoid traits are used in
ecological or evolutionary studies focussed at the individual level.