Data from: Macroevolutionary patterning in glucocorticoids suggests different selective pressures shape baseline and stress-induced levels

Glucocorticoid (GC) hormones are important phenotypic mediators across
vertebrates, but their circulating concentrations can vary markedly. Here
we investigate macroevolutionary patterning in GC levels across tetrapods
by testing seven specific hypotheses about GC variation, and evaluating
whether the supported hypotheses reveal consistent patterns in GC
evolution. If selection generally favors the “supportive” role of GCs in
responding effectively to challenges, then baseline and/or stress-induced
GCs may be higher in challenging contexts. Alternatively, if selection
generally favors “protection” from GC-induced costs, GCs may be lower in
environments where challenges are more common or severe. The predictors of
baseline GCs were all consistent with supportive effects: levels were
higher in smaller organisms, and in those inhabiting more energetically
demanding environments. During breeding, baseline GCs were also higher in
populations and species with fewer lifetime opportunities to reproduce.
The predictors of stress-induced GCs were instead more consistent with the
protection hypothesis: during breeding, levels were lower in organisms
with fewer lifetime reproductive opportunities. Overall, these patterns
indicate a surprising degree of consistency in how some selective
pressures shape GCs across broad taxonomic scales; at the same time, in
challenging environments selection appears to operate on baseline and
stress-induced GCs in distinct ways.