Telomeres as biomarkers of cost and quality in a wild vertebrate population

因为资源和获取资源所需的时间是有限的，所以每个生物体都有有限的数量可以用于生存和繁殖。花在一个领域，如保健领域的资源不能花在另一个领域，如生殖领域。因此，生物体必须权衡如何最好地利用它们的资源，以最大限度地获得利益。这种权衡对于我们理解不同生命史策略的进化至关重要，即为什么生物体在大小，繁殖率和寿命等方面存在差异/生物学中的一个基本问题。问题在于，尽管评估在一个领域投资对一个有机体的好处往往相对容易，但要理解权衡取舍，我们还需要知道相关的成本。不幸的是，测量这种成本已被证明是极其困难的，特别是在野生动物中。此外，要找出哪些机制将替代投资的成本联系起来，并在投资领域之间或在生物体的整个生命周期中进行权衡，已经证明是我们所无法做到的。端粒是DNA的长而专门的区域，它保护染色体的末端，并防止细胞的基因在每次细胞复制时受损或混淆。然而，在每次复制过程中，端粒的一部分会丢失，当端粒达到一个临界的短长度时，细胞就会停止运作。这些功能失调的细胞在身体组织中的积累被认为会导致衰老和衰老。重要的是，端粒缩短的速率也受到氧化应激/生物体无法科普代谢的破坏性废物（自由基）的极大影响。氧化应激（和/或端粒缩短）已被证明受到生活史和环境应激（例如加速生长或感染）的影响。因此，端粒缩短可以表明这种压力对个体的生物成本，并在这些成本与衰老和衰老之间提供重要联系。我们计划利用塞舌尔莺上编制的独特数据集，借此机会对野生脊椎动物种群中的个体进行端粒的纵向研究。我们之所以能够做到这一点，是因为对该物种岛屿种群的深入长期研究意味着可以获得关于所经历的环境因素和所作生殖投资的非常详细的信息。重要的是，每年都从许多已知年龄的个体中收集血液样本。首先，我们将重点关注端粒缩短是否可以作为衡量野生种群生物衰老的一个指标。这一点的关键是确认与年龄相关的个体端粒长度预测塞舌尔莺的寿命（和/或衰老）。然后，我们将通过将每年的端粒缩短率与他们当年面临的压力联系起来，研究不同压力的相对成本。实验操作将使我们能够磨练特定的因素，如生殖努力。重要的是，成本将用通用货币单位（端粒缩短率）来衡量，这不仅可以在压力之间进行比较，还可以在经历压力的年龄和生活史阶段方面进行比较。这将使我们能够比较在不同生命史组成部分或处理环境压力方面投资的成本和收益如何权衡。最后，我们将测试端粒缩短率的个体差异可以反映个体承受这些压力的能力，从而提供个体质量的指标。

Because resources, and the time it take to acquire them, are limited, every organism has a finite amount it can use in its efforts to survive and reproduce. Resources spent on one area, such as health, cannot be spent on another, such as in reproduction. Consequently organisms must trade off how best to spend their resources so as to maximise the benefits they gain. Such trade-offs are central to our understanding of the evolution of different life-history strategies, i.e. why organisms differ in aspects such as their size, reproductive rate and lifespan / a fundamental question in biology. The problem is that, although it is often relatively easy to assess the benefit to an organism of investing in one area, to understand trade-offs we also need to know the associated cost. Unfortunately, measuring such costs has proved to be extremely difficult, especially in animals in the wild. Furthermore, working out which mechanisms link the costs of alternative investments, and mediate trade-offs between areas of investment, or across the lifetime of an organism, has proved beyond us. Telomeres are long, specialized regions of DNA that protect the ends of chromosomes and prevent the cells' genes from getting damaged or mixed up each time the cell replicates. However, a section of telomere is lost during each replication and when telomeres reach a critical, short length the cell stops functioning. The accumulation of these dysfunctional cells in the bodies' tissues is thought to lead to ageing and senescence. Importantly the rate at which telomeres shorten is also greatly affected by oxidative stress / the organism's inability to cope with the damaging waste products (free radicals) of metabolism. Oxidative stress (and/or telomere shortening) has been shown to be influenced by life history and environmental stresses (e.g. accelerated growth or infection). Telomere shortening can, therefore, indicate the biological cost that such stresses exact on an individual and provide an important link between these costs and ageing and senescence. We plan to use the unique dataset compiled on the Seychelles warblers to take the opportunity to undertake a longitudinal study of telomeres within individuals in a wild vertebrate population. We are only able to do this because the intensive long-term study of island populations of this species means that highly detailed information is available on the environmental factors experienced and reproductive investments made. Importantly, annual blood samples have been collected from many individuals of known age throughout their lives. First, we will focus on whether telomere shortening can be used as a measure of biological ageing in a wild population. Key to this is confirming that age-related lengths of an individual's telomeres predicts lifespan (and/or senescence) in the Seychelles warbler. We will then investigate the relative costs of different stresses by relating the annual telomere-shortening rate to the stresses they have faced in that year. Experimental manipulations will allow us to hone in on specific factors, such as reproductive effort. Importantly, costs will be measured with generic units of currency (telomere shortening rates) that would allow comparisons, not only between stresses, but also with respect to the age and life-history stage at which they are experienced. This will allow us to compare how the costs and benefits of investment in different life-history components, or in dealing with environmental stresses, are traded off. Finally, we will test the idea that individual variation in telomere shortening rate can reflect an individual's ability to withstand these stresses and, therefore, provide an indicator of individual quality.