Data from: Brood size, telomere length, and parent-offspring color signaling in barn swallows

Trade-offs select for optimal allocation of resources among competing functions. Parents are selected to maximize production of viable offspring by balancing between progeny number and “quality.” Telomeres are nucleoproteins, at the ends of eukaryotic chromosomes, that shorten when cells divide. Because shortening below a certain threshold depresses organismal functioning and rate of shortening depends on environmental conditions, telomeres are good candidates as mediators of trade-offs. We altered brood size of barn swallow Hirundo rustica and found that brood enlargement caused a reduction in relative telomere length (RTL). Reliable signals of offspring quality should evolve that mediate adaptive parental care allocation. Because nestlings with darker coloration receive more care, we analyzed the covariation between RTL and coloration and found that RTL increased with plumage darkness, both within and between broods. Hence, we provide unprecedented evidence that signals relevant to parent-offspring communication reflect telomere length and thus offspring reproductive value.

权衡机制驱动竞争功能间的资源最优分配。自然选择促使亲本通过权衡后代数量与“质量”，最大化存活后代的产出。端粒（Telomeres）是真核染色体末端的核蛋白复合物，细胞分裂时其长度会发生缩短。当端粒缩短至特定阈值以下时会损害机体功能，且缩短速率受环境条件调控，因此端粒是介导权衡效应的理想候选靶点。我们通过调整家燕（Hirundo rustica）的窝雏数，发现窝雏数增加会导致相对端粒长度（RTL）降低。能够介导适应性育幼资源分配的后代质量可靠信号，理应通过演化得以保留。由于羽色更深的雏鸟能获得更多亲代抚育，我们分析了相对端粒长度与羽色的协变关系，结果显示无论在同窝雏鸟间还是不同窝雏鸟间，相对端粒长度均随羽色加深而增加。因此，本研究首次提供了确凿证据：亲代-子代交流相关的信号能够反映端粒长度，进而体现后代的繁殖价值。