Early-life stress strengthens trait covariance: a plastic response that results in reduced flexibility

Stress exposure during development can impact both the expression of individual traits and associations between traits, but whether stress results in stronger or weaker associations between traits is unclear. In this study, we examined within and among-trait associations for morphological and physiological traits in zebra finches (Taeniopygia guttata) exposed to corticosterone (CORT) during the nestling and fledgling stages, and in control birds. Birds exposed to CORT exhibited stronger correlations within traits and stronger associations among traits. We found preliminary evidence that birds that died before the median age of death had stronger within and among-trait correlations independent of treatment, and among CORT-treated birds, smaller birds were more likely to survive beyond the median age than larger birds. These findings suggest that early-life stress hormone exposure can result in reduced developmental flexibility, with potential fitness ramifications, and that these costs m...