Repeated experimental challenges do not shorten adult telomeres in a songbird.

Responding to environmental challenges can have both positive and negative effects on fitness, but the mechanisms and/or biomarkers underlying these links are not well understood. Telomeres-repetitive sections of DNA that form protective caps at chromosome ends, which enhance genome integrity and often predict organismal lifespan-may be important in this context. Some evidence suggests that stress exposure shortens telomeres, but most studies are correlational and/or conducted during early life; thus, how stress exposure influences telomeres in adulthood is not well known. Here, we experimentally exposed wild-captured adult house sparrows (Passer domesticus) to a series of standardized protocols of repeated, rotating stressors (including threats, unpredictable food availability and immune challenges) designed to increase stress levels. Although there were some effects of the treatment on glucocorticoid levels and mass dynamics, there were no effects on telomeres during any of the 6-11-month studies. Taken together, these results suggest that telomeres are robust or resilient to a range of stressors in adulthood. The effects of stress exposures on telomeres are likely to be highly context-dependent and to vary depending on the timing, intensity and duration of the stress exposures, as well as an individual's life stage.