Causes and consequences of variation in early‐life telomere length in a bird metapopulation

Environmental conditions during early-life development can have lasting
effects shaping individual heterogeneity in fitness and fitness-related
traits. The length of telomeres, the DNA sequences protecting chromosome
ends, may be affected by early-life conditions, and telomere length (TL)
has been associated with individual performance within some wild animal
populations. Thus, knowledge of the mechanisms that generate variation in
TL, and the relationship between TL and fitness, is important in
understanding the role of telomeres in ecology and life-history evolution.
Here, we investigate how environmental conditions and morphological traits
are associated with early-life blood TL and if TL predicts natal dispersal
probability or components of fitness in 2746 wild house sparrow (Passer
domesticus) nestlings from two populations sampled across 20 years
(1994-2013). We retrieved weather data and we monitored population
fluctuations, individual survival, and reproductive output using field
observations and genetic pedigrees. We found a negative effect of
population density on TL, but only in one of the populations. There was a
curvilinear association between TL and the maximum daily North Atlantic
Oscillation index during incubation, suggesting that there are optimal
weather conditions that result in the longest TL. Dispersers tended to
have shorter telomeres than non-dispersers. TL did not predict survival,
but we found a tendency for individuals with short telomeres to have
higher annual reproductive success. Our study showed how early-life TL is
shaped by effects of growth, weather conditions, and population density,
supporting that environmental stressors negatively affect TL in wild
populations. In addition, shorter telomeres may be associated with a
faster pace-of-life, as individuals with higher dispersal rates and annual
reproduction tended to have shorter early-life TL.