Early-life telomere length predicts lifespan and lifetime reproductive success in a wild bird.

Poor conditions during early development can initiate trade-offs that favour current survival at the expense of somatic maintenance and subsequently, future reproduction. However, the mechanisms that link early and late life-history are largely unknown. Recently it has been suggested that telomeres, the nucleoprotein structures at the terminal end of chromosomes, could link early-life conditions to lifespan and fitness. In wild purple-crowned fairy-wrens, we combined measurements of nestling telomere length (TL) with detailed life-history data to investigate whether early-life TL predicts fitness prospects. Our study differs from previous studies in the completeness of our fitness estimates in a highly philopatric population. The association between TL and survival was age-dependent with early-life TL having a positive effect on lifespan only among individuals that survived their first year. Early-life TL was not associated with the probability or age of gaining a breeding position. Interestingly, early-life TL was positively related to breeding duration, contribution to population growth and lifetime reproductive success because of their association with lifespan. Thus, early-life TL, which reflects growth, accumulated early-life stress and inherited TL, predicted fitness in birds that reached adulthood but not noticeably among fledglings. These findings suggest that a lack of investment in somatic maintenance during development particularly affects late life performance. This study demonstrates that factors in early-life are related to fitness prospects through lifespan, and suggests that the study of telomeres may provide insight into the underlying physiological mechanisms linking early- and late-life performance and trade-offs across a lifetime.