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.

权衡机制经自然选择，可使生物在相互竞争的生理功能间实现最优资源分配。自然选择倾向于促使亲代通过平衡子代数量与‘质量’，最大化存活子代的产出。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。由于端粒缩短至特定阈值以下会损害机体功能，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因子。我们以家燕（Hirundo rustica）为研究对象，调整其窝雏数后发现，窝雏数增加会导致相对端粒长度（relative telomere length, RTL）降低。能够介导适应性育幼资源分配的子代质量可靠信号，应通过演化得以保留。由于羽色更深的雏鸟会获得更多亲代抚育，我们分析了相对端粒长度与羽色间的协变关系，结果显示无论在同窝雏鸟内部还是不同窝雏鸟之间，相对端粒长度均随羽色加深而增加。因此，本研究提供了前所未有的确凿证据，表明与亲子交流相关的信号能够反映端粒长度，进而体现子代的繁殖价值。