Evolution of Marine Mammal Foraging Behavior Based on Ca and C Isotope Ratios in Bioapatite

虽然已知海洋生态系统的营养结构随着时间的推移变得越来越复杂，但缺乏量化这种变化的方法。本研究将在利用钙同位素比率作为古生态指标的初步工作基础上进行扩展，并发展该同位素系统作为已灭绝海洋哺乳动物营养水平的代表。结合海洋生态系统中Ca同位素和C同位素比值随觅食生境的变化而变化，为研究古代海洋脊椎动物生态系统的结构提供了一种新的手段。由于食物网的营养结构对营养物质和能量在生态系统内部和之间移动的途径有重要影响，分析生物源硬部分的Ca同位素组成可能有助于阐明营养循环和能量流动如何随时间波动。此外，通过扩大对古代生态系统如何运作以及它们与当今生态系统有何不同的现有知识，a44Ca测量可以帮助改进对气候和环境扰动如何影响或受地球生物圈影响的解释。最终，这个项目将为鲸鱼的进化提供新的见解，它们从陆地祖先进化而来，代表了地球生命史上最显著的转变之一。虽然本研究的最终目的是了解鲸目动物（包括现存的鲸、鼠海豚和海豚）的进化过程中时间变化对行为的影响，但在将Ca同位素比值应用于灭绝物种之前，必须首先在现代物种中研究营养水平以外的因素对Ca同位素比值的影响。海洋哺乳动物的四个远亲类群（海鲸类、鼬类、鲸类和鳍足类）的样本将被分析，作为解决系统发育历史对a44Ca值影响的一种手段；在同一营养水平的物种中，a44Ca值的相似程度将验证a44Ca值是否反映了营养水平的差异，而不考虑进化史。每个样品的C同位素组成将被分析作为觅食栖息地偏好的代理；a44Ca与营养水平的相关性强于与a13c值的相关性，说明营养水平对a44Ca值的影响大于物种觅食习性的影响。通过分析来自四个现代海洋哺乳动物样本中每个个体的多个骨骼元素的Ca同位素组成，将探索单个个体中a44Ca的变化。在确定影响现代海洋哺乳动物a44Ca值的因素后，将分析始新世和渐新世鲸类和西雷世生物磷灰石的Ca和C同位素组成，以评估这一代用物在古生态研究中的潜力。渐新世鲸类摄食策略的多样化应该与鲸类生物磷灰石的a44Ca和a13C值的巨大变化相吻合，这为原始的a44Ca值是否可以保存和从化石记录中解释提供了明确的信号。sirenians的骨骼化石也将作为海水中a44Ca值潜在变化的对照物进行分析，因为该群体的营养水平随时间保持不变，并且该群体的a44Ca值的任何变化都将反映海水中a44Ca值的变化。更广泛的影响。这个项目的广泛影响是三重的。首先，这笔资金将用于培养和发展新近获得博士学位的博士后。在pi的监督下，该研究人员将主要负责改进方法，获取和分析样本，解释和传播结果。其次，该研究将为更广泛的群落提供一个新的和潜在的强大的古生态工具，可以应用于其他古代海洋生态系统，并在进一步发展后，也可能应用于地际生态系统。最后，这些结果将补充我们对鲸鱼进化的日益详细的了解。一旦拟议的研究完成，与鲸鱼进化相关的生态和形态变化将成为脊椎动物化石记录中宏观进化变化的最佳记录案例之一。鉴于鲸鱼起源在反进化论战中的历史地位，这项研究肯定会对本科和K-12课堂产生持久的影响。

Though the trophic structure of marine ecosystems is known to haveincreased in complexity over time, methods of quantifying this change are lacking. The proposedresearch will expand upon promising preliminary work using Ca isotope ratios as paleoecologicalindicators and develop this isotopic system as a proxy for the trophic level of extinct marine mammals.By combining Ca isotope analyses with C isotope ratios, which vary with foraging habitat in marineecosystems, this project will provide a new means to examine the structure of ancient marine vertebrateecosystems. Since the trophic structure of foodwebs has a significant influence on the pathways by whichnutrients and energy move within and between ecosystems, analysis of the Ca isotope composition ofbiogenic hard parts may aid in elucidating how nutrient cycling and energy flow have fluctuated overtime. Furthermore, by expanding current knowledge of how ancient ecosystems functioned and how theydiffered from today s ecosystems, a44Ca measurements can help improve interpretations of how climaticand environmental perturbations have impacted or were impacted by the Earth s biosphere. Ultimately,this project will provide new insight into the evolution of whales, whose from a terrestrial ancestorrepresents one of the most remarkable transitions in the history of life on Earth.Although the ultimate objective of this research is to understand the role of temporal changes inforaging behavior in the evolution of Cetacea (the clade that includes living whales, porpoises, anddolphins), the influence on Ca isotope ratios of factors other than trophic level must be examined first inmodern species before Ca isotope ratios can be applied to extinct species. Samples of marine mammals infour, distantly related groups (sirenians, mustellids, cetaceans, and pinnipeds) will be analyzed as a meansof addressing the impact of phylogenetic history on a44Ca values; the degree of similarity of a44Ca valuesfor species at the same trophic level will verify whether a44Ca values reflect trophic level differencesregardless of evolutionary history. The C isotope composition of each sample will be analyzed as a proxyfor foraging habitat preference; a stronger correlation between a44Ca with trophic level rather than a13Cvalues will indicate that trophic level has a stronger influence on a44Ca values than the foraging habits ofa species. Variation in a44Ca within a single individual will be explored by analyzing the Ca isotopecomposition of multiple skeletal elements from a single individual from each of the four modern groupsof marine mammals sampled. Once the factors influencing a44Ca values in modern marine mammalshave been constrained, the Ca and C isotope composition of Eocene and Oligocene cetacean and sirenianbioapatite will be analyzed to assess the potential of this proxy for paleoecological studies. Thediversification of cetacean feeding strategies in the Oligocene should coincide with a large change ina44Ca and a13C values of cetacean bioapatite, providing a clear signal of whether original a44Ca values canbe preserved and interpreted from the fossil record. Fossil bones of sirenians will also be analyzed as acontrol for potential changes in seawater a44Ca values, since the trophic level of this group has remainedconstant over time and any changes in the a44Ca values of this group will reflect changes in seawatera44Ca values.Broader impacts. The broader impacts of this project are threefold. First, the grant will furtherthe training and development of a recent Ph.D. who will be supported as a postdoc. Under thesupervision of the PIs, this researcher will have primary responsibility for refining the methodologies,acquiring and analyzing the samples, and interpreting and disseminating the results. Second, the researchwill provide a new and potentially powerful paleoecological tool to the broader community that can beapplied to other ancient marine ecosystems and, after further development, may also have applications interrestrial ecosystems. Finally, the results will complement our increasingly detailed knowledge of whaleevolution. Once the proposed research is completed, the ecological and morphological changesassociated with the evolution of whales will be one of the best documented cases of macroevolutionarychange in the vertebrate fossil record. Given the historical place of whale origins in anti-evolutionpolemics, this research will surely have lasting impact in undergraduate and K-12 class rooms.