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

基于氨基酸的同位素方法研究古代生态系统动力学[j]；联合检察官：丽贝卡·s·罗宾逊；这个提议背后的想法是开发一种方法，通过这种方法我们可以测量骨骼和牙齿化石中氨基酸的氮同位素组成。已经证明15N/14N的量(我们测量为？Ô15N)增加食物链中的每一个营养步骤。这实际上意味着15N/14N比率在初级生产者中最低（在陆地领域，这通常意味着植物），并且在那些以初级生产者为食的生物中增加，并且在那些以初级生产者为食的动物为食的动物中进一步增加。那么？Ô15N签名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方法。这项技术的发展机制，实际上是本提案的重点，充满了问题。其中最重要的是污染和体积。污染问题与困扰所有古代分子研究的问题是一样的：很有可能？Ô15N我们得到的数字可能来自更年轻的生物，甚至可能是那些生活在今天的生物，如果是这样的话，他们的？Ô15N签名显然是错误的。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，我们至少看到了古老的、保存下来的分子。这就引出了体积问题，因为如果我们看？Ô15N签名只是一个特定系列的可识别的氨基酸，那么我们显然需要处理小得多的样本，如果我们看的是散装，或总，？Ô15N特定牙齿或骨头的特征。此外，在分子老化过程中发生的降解过程中，某些氨基酸被优先保留，而其他氨基酸则丢失。通过靶向特定氨基酸（最好不止一种）并追踪它们的？Ô15N通过食物网签名，我们将提供比传统有机食品方法更可靠的饮食关系图。氮同位素分异作为营养地位的记录已在海洋和陆地生态系统中反复得到证实。随着这项建议所支持的技术的发展，我们期望有一个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，该技术在研究古代生态系统方面具有广泛的应用。

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.