Increased glucocorticoid concentrations in early life cause mitochondrial inefficiency and short telomeres

Telomeres are DNA structures that protect chromosome ends. However, telomeres shorten during cell replication and at critically low lengths can reduce cell replicative potential, induce cell senescence and decrease fitness. Stress exposure, which elevates glucocorticoid hormone concentrations, can exacerbate telomere attrition. This phenomenon has been attributed to increased oxidative stress generated by glucocorticoids (\"oxidative stress hypothesis\"). We recently instead suggested that glucocorticoids increase telomere attrition during stressful periods by reducing the resources available for telomere maintenance through changes in the metabolic machinery (\"metabolic telomere attrition hypothesis\"). Here we tested whether experimental increases in glucocorticoid levels affected telomeres and mitochondrial function in wild great tit (Parus major) nestlings during the energy-demanding early growth. We monitored resulting corticosterone (Cort) concentrations in plasma, and in red blood c...