Telomere length and telomere shortening predict survival in many organisms. This raises the question of the contribution of genetic and environmental effects to variation in these traits, which is still poorly known, particularly for telomere shortening. We used experimental (cross-fostering) and statistical (quantitative genetic “animal models”) means to disentangle and estimate genetic and environmental contributions to telomere length variation in pedigreed free-living jackdaws (Corvus monedula). Telomere length was measured twice in nestlings, at ages 4 (n = 715) and 29 days (n = 474), using telomere restriction fragment (TRF) analysis, adapted to exclude interstitial telomeric sequences. Telomere length shortened significantly over the nestling period (10.4 ± 0.3 bp day^–1) and was highly phenotypically (r_P = 0.95 ± 0.01) and genetically (r_G > 0.99 ± 0.01) correlated within individuals. Additive genetic effects explained a major part of telomere length variation among individuals, with its heritability estimated at h² = 0.74 on average. We note that TRF-based studies reported higher heritabilities than qPCR-based studies, and we discuss possible explanations. Parent–offspring regressions yielded similar heritability estimates for mothers and fathers when accounting for changes in paternal telomere length over life. Year effects explained a small but significant part of telomere length variation. Heritable variation for telomere shortening was low (h² = 0.09 ± 0.11). The difference in heritability between telomere length (high) and telomere shortening (low) agrees with evolutionary theory, in that telomere shortening has stronger fitness consequences in this population. Despite the high heritability of telomere length, its evolvability, which scales the additive genetic variance by mean telomere length, was on average 0.48%. Hence, evolutionary change of telomere length due to selection is likely to be slow.

中文翻译：

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野生鸟类端粒长度的高遗传性和端粒缩短的低遗传性

端粒长度和端粒缩短可预测许多生物体的存活率。这就提出了遗传和环境影响对这些性状变异的贡献的问题，这仍然鲜为人知，特别是端粒缩短。我们使用实验（交叉培育）和统计（定量遗传“动物模型”）方法来解开和估计遗传和环境对纯种自由生活寒鸦 (Corvus monedula) 端粒长度变化的贡献。在 4 岁（n  = 715）和 29 天（n = 474)，使用端粒限制性片段 (TRF) 分析，适用于排除间质性端粒序列。端粒长度在雏鸟期显着缩短（10.4 ± 0.3 bp day ^–1）并且在表型上（r _P  = 0.95 ± 0.01）和遗传上（r _G  > 0.99 ± 0.01）在个体内高度相关。加性遗传效应解释了个体间端粒长度变异的主要部分，其遗传力估计为h ² = 0.74 平均。我们注意到基于 TRF 的研究报告的遗传力高于基于 qPCR 的研究，我们讨论了可能的解释。当考虑到父亲端粒长度在一生中的变化时，父母-后代回归对母亲和父亲产生了相似的遗传力估计。年份效应解释了端粒长度变化的一小部分但很重要的部分。端粒缩短的遗传变异很低 ( h ² = 0.09 ± 0.11)。端粒长度（高）和端粒缩短（低）之间的遗传力差异与进化论一致，因为端粒缩短在该人群中具有更强的适应性结果。尽管端粒长度具有很高的遗传力，但其可进化性（通过平均端粒长度衡量加性遗传方差）平均为 0.48%。因此，由选择引起的端粒长度的进化变化可能是缓慢的。