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An individual's telomere length early in life may reflect or contribute to key life‐history processes sensitive to environmental variation. Yet, the relative importance of genetic and environmental factors in shaping early‐life telomere length is not well understood as it requires samples collected from multiple generations with known developmental histories. We used a confirmed pedigree and conducted an animal model analysis of telomere lengths obtained from nestling house sparrows (Passer domesticus) sampled over a span of 22 years. We found significant additive genetic variation for early‐life telomere length, but it comprised a small proportion (9%) of the total biological variation. Three sources of environmental variation were important: among cohorts, among‐breeding attempts within years, and among nestmates. The magnitude of variation among breeding attempts and among nestmates also differed by cohort, suggesting that interactive effects of environmental factors across time or spatial scales were important, yet we were unable to identify the specific causes of these interactions. The mean amount of precipitation during the breeding season positively predicted telomere length, but neither weather during a given breeding attempt nor date in the breeding season contributed to an offspring's telomere length. At the level of individual nestlings, offspring sex, size and mass at 10 days of age also did not predict telomere length. Environmental effects appear especially important in shaping early‐life telomere length in some species, and more focus on how environmental factors that interact across scales may help to explain some of the variation observed among studies.

 

The mechanisms that contribute to variation in lifetime reproductive success are not well understood. One possibility is that telomeres, conserved DNA sequences at chromosome ends that often shorten with age and stress exposures, may reflect differences in vital processes or influence fitness. Telomere length often predicts longevity, but longevity is only one component of fitness and little is known about how lifetime reproductive success is related to telomere dynamics in wild populations. We examined the relationships between telomere length beginning in early life, telomere loss into adulthood and lifetime reproductive success in free-living house sparrows ( Passer domesticus ). We found that females, but not males, with longer telomeres during early life had higher lifetime reproductive success, owing to associations with longevity and not reproduction per year or attempt. Telomeres decreased with age in both sexes, but telomere loss was not associated with lifetime reproductive success. In this species, telomeres may reflect differences in quality or condition rather than the pace of life, but only in females. Sexually discordant selection on telomeres is expected to influence the stability and maintenance of within population variation in telomere dynamics and suggests that any role telomeres play in mediating life-history trade-offs may be sex specific. 

Telomeres, protective caps at the end of chromosomes, are often positively related to lifespan and are thought to be an important mechanism of organismal aging. To better understand the casual relationships between telomere length and longevity, it is essential to be able to experimentally manipulate telomere dynamics (length and loss rate). Previous studies suggest that exposure to TA‐65, an extract from the Chinese rootAstragalus membranaceus, activates telomerase, lengthens telomeres, increases the growth of keratin‐based structures, and boosts the immune system in adults. However, telomere loss is expected to be greatest during early life but whether TA‐65 has similar effects during this life stage is currently unknown. Here, we experimentally exposed free‐living house sparrow (Passer domesticus) chicks to TA‐65 during post‐natal development and examined the effects on telomere length and loss, growth of keratin‐based structures, and a measure of cellular immunity. Contrary to expectation, the growth of keratin‐based structures was reduced in TA‐65 chicks and in the second year of the study, chicks exposed to TA‐65 experienced more telomere loss than controls. Thus, the effects of TA‐65 on telomeres and keratin‐based structures differ across life stages and future research will be necessary to determine the mechanisms underlying these age‐specific effects.