Developmental Heat Conditioning Alters the Adult Glucocorticoid Response and DNA Damage While Mediating Lifespan Variation in Zebra Finches (Taeniopygia Castanotis)

Developmental stressors may result in adaptive adjustments in physiology, increasing fitness later in life in otherwise damaging environments. Environmental conditions during development can permanently alter the responsiveness of the hypothalamic-pituitary-adrenal (HPA) axis, which may allow organisms to avoid cellular damage in stressful conditions. We hypothesized that zebra finches (Taeniopygia guttata castanotis) thermally conditioned during development will have lower baseline plasma corticosterone (cort) and baseline erythrocyte DNA damage as adults, as well as lower post-stressor cort and DNA damage, and higher survival rates following a thermal stressor in adulthood compared to juvenile controls. To test this, we exposed juvenile male and female zebra finches to a mild heat (38°C) or control (22°C) temperature every other day for 28 days. As adults, these finches were then subjected to either a high heat stressor (42°C) or control (22°C) temperature for 3 consecutive days. We measured plasma cort levels and erythrocyte genomic DNA damage before and at the end of each treatment period. As adults, the heat-conditioned juvenile finches had higher baseline DNA damage levels, persistently higher body masses, and lower cort levels 4 h following the adult high heat stress treatment compared to juvenile controls. Moreover, this cort phenotype was associated with reduced body mass loss and increased survival rates. However, females had reduced survival if they were not also exposed to the high heat treatment as adults. Our results demonstrate adaptive developmental plasticity in cort levels; however, this phenotype may be detrimental when there is an environmental mismatch.