SGER: An Amino Acid-based Isotopic Method for Studying the Dynamics of Ancient Ecosystems

一种以氨基酸为基础的研究古代生态系统动力学的同位素方法PI：David E.Fastovsky；Co-PI：Rebecca S.Robinson；Steven L.D.Hond这一建议背后的想法是开发一种方法，用来测量化石骨骼和牙齿中氨基酸的氮同位素组成。已有研究表明，食物链中的每一个营养步骤，15N/14N(我们测量为15N)的量都会增加。这实际上意味着15N/14N在初级生产者中最低(在陆地领域，这通常意味着植物)，在那些吃初级生产者的有机体中增加，在那些吃初级生产者的动物中甚至进一步增加。因此，15N标记实际上是一种测量长期灭绝的生物在长期灭绝的生态系统中发挥作用的水平的一种方法。这项技术的发展机制，实际上是这项提议的要点，充满了问题。其中最重要的是污染和数量。污染问题是困扰所有古代分子研究的问题：我们获得的15N数字很有可能来自更年轻的生物体--甚至可能是今天的生物--如果是这样的话，他们的15N标记显然是错误的。为了避免这种可能性，我们希望从已知分子中获得氮。我们选择对每颗牙齿使用氨基酸特征图谱，这将告诉我们，我们至少在寻找古老的、保存完好的分子。这就把我们带到了体积问题上，因为如果我们只研究一系列特定可识别氨基酸的15N签名，那么我们显然需要处理比我们查看特定牙齿或骨骼的整体或全部15N签名要小得多的样本。此外，在随着分子老化而发生的降解过程中，某些氨基酸优先保持，而其他氨基酸则丢失。通过针对特定的氨基酸(最好是不止一种)并通过食物网追踪它们的15N特征，我们将提供比传统的大宗有机方法所允许的更可靠的饮食关系图景。氮同位素作为营养位置的记录在海洋和陆地生态系统中得到了反复的证明。随着这项提议支持的技术的发展，我们预计会有一种精确的同位素工具来识别(并避免)由于化石材料的改变或污染而产生的问题。因此，这项技术在研究古代生态系统方面有着广泛的应用。

An amino acid-based isotopic method for studying the dynamics of ancient ecosystemsPI: David E. Fastovsky; Co-PIs: Rebecca S. Robinson; Steven L. D¡¦HondtThe idea behind this proposal is to develop a method by which we can measure the nitrogen isotopic composition of amino acids from fossil bones and teeth. It has been shown that the amount of 15N/14N (which we measure as ?Ô15N) increases each trophic step in a food chain. This means in effect that the 15N/14N ratio is lowest among primary producers (in the terrestrial realm, this generally means plants), and increases in those organisms that eat the primary producers, and increases even further in those animals that eat the animals that eat the primary producers. So the ?Ô15N signature is actually a way to measure at which levels long-extinct organisms functioned in long-extinct ecosystems.The mechanics of the development of this technique, which is in fact the point of this proposal, is fraught with problems. Most significant among these are contamination and volume. The contamination problem is the same one that plagues all studies of ancient molecules: there is a very real possibility that the ?Ô15N numbers that we obtain could come from younger organisms ¡V possibly even those living today ¡V and if so their ?Ô15N signatures would obviously be wrong. To avoid this possibility, we would like to obtain our nitrogen from known molecules. We have chosen to use an amino acid signature profile for each tooth, which would tell us that we are at least looking at ancient, preserved molecules. This takes us to the volume problem, because if we are looking at the ?Ô15N signature for just a particular series of identifiable amino acids, then we are obviously required to deal with much smaller samples than if we were looking at the bulk, or total, ?Ô15N signature of a particular tooth or bone. Moreover, during the degradation that takes place as molecules age, certain amino acids are preferentially maintained while others are lost. By targeting of specific amino acids (preferably more than one) and tracing their ?Ô15N signatures through a food web, we will provide a much more reliable picture of dietary relationships than traditional bulk-organic methods allow.The fractionation of nitrogen isotopes as a record of trophic position has been repeatedly demonstrated for both marine and terrestrial ecosystems. With the development of the technique this proposal supports, we anticipate having a precise isotopic tool that identifies (and avoids) problems due to alteration or contamination of fossil material. For this reason, the technique has broad applications for studying ancient ecosystems.