Collaborative Research: Elements of an extinction: Exploring the delayed Caribbean extinction with stable isotopes and trace elements

生物学家警告说，目前生态系统的退化和破碎化将导致未来很长一段时间的灭绝--这一过程被称为“灭绝债”--但要做出准确的预测，需要更好地了解灭绝在长期时间尺度上是如何发生的。该项目将剖析加勒比西南部上新世-更新世灭绝事件（1-2百万年），以研究环境扰动与灭绝率之间的关系。在上新世-更新世事件期间，加勒比海各种海洋生物的灭绝率达到35%至100%的峰值。更好地适应营养丰富的条件的类群受到的影响最大。因此，物种灭绝通常归因于中美洲地峡关闭后，加勒比海水域与太平洋隔离，导致海水中的营养物质减少。然而，灭绝的时间比结束的时间晚了1- 200万年，导致一些研究人员将灭绝率的增加归因于与北方冰川作用开始有关的气候变化。这项研究将综合生物和地球化学数据，以揭示加勒比灭绝事件的直接原因，并利用巴拿马古生物学项目提供的既有和新的古环境代用指标以及前所未有的采样广度和分类分析深度，评价所认为的延迟的证据。三个假设将进行测试：（1）注定要生存的类群在营养丰富的避难所，坚持地峡关闭后，灭绝发生避难所充分减少。(2)灭绝是由与北方冰川作用有关的冷却驱动的。(3)暂时生存注定类群是无关的营养物质或温度的变化，这表明随机过程负责。为了实现这一目标，我们将产生高分辨率的稳定同位素（18 O/16 O，13 C/12 C）配置文件的~90腹足类贝壳从26个化石地点在SWC约会5和1.4 Ma之间，辅以成团同位素（13 C18 O/12 C16 O）和微量元素（P/Ca，Sr/Ca，Ba/Ca）分析，以确定过去的当地温度和营养物质的可用性。该项目将是第一个利用热带美洲化石记录和多个高分辨率地球化学代用指标建立一个约束良好的环境系统的项目，以测试一系列进化假设。这些包括负责物种形成，灭绝，生态位扩张和有性生殖的进化维持的过程。将生物数据与详细的古环境数据结合起来，将揭示地质学上最近的海洋灭绝的根本原因，并提供一个真实的例子来测试大规模生物多样性丧失过程的模型。现代人为破碎的自然栖息地和人口反映了避难所，据称有推迟灭绝的SWC类群在上新世。我们的数据将评估这一假设，并证明是否在生物多样性的损失是直接相关的环境changes.The项目将整合到在得克萨斯州A M大学（TAMU）的地球科学环境计划的本科课程的顶点巴拿马为基础的实地经验。学生将分组工作，对他们在巴拿马收集的样本进行古生物学和稳定同位素研究，并在TAMU进行采样和分析。除了展示结果，学生还将撰写，同行评审和修改研究论文。该项目将在跨学科科学和研究指导方面培训一名博士后研究员和一名研究生。最后，研究成果将在主要的国家和国际会议上发表，并在一流的期刊上发表。

Biologists warn that the current degradation and fragmentation of ecosystems will lead to extinctions long into the future -- a process dubbed 'Extinction debt' --but making accurate predictions requires a much better understanding of how extinctions occur over long-term time scales. This project will dissect the Plio-Pleistocene extinction event (1-2 Myr) in the southwestern Caribbean (SWC) to examine the relationship between environmental perturbation and extinction rate. During the Plio-Pleistocene event, extinction rates peaked between 35 and 100% in a variety of marine taxa across the Caribbean. Taxa better adapted to nutrient-rich conditions were impacted most. Thus, the extinction is often attributed to declining planktic nutrients in Caribbean water due to isolation from the Pacific after the closure of the Central American Isthmus. The extinctions lagged closure by 1-2 Myr, however, leading some researchers to attribute increased extinction rates to climate change associated with the onset of northern hemisphere glaciation. This study will integrate biotic and geochemical data to reveal the direct causes of the Caribbean extinction event and evaluate the evidence for the perceived delay using established and new paleoenvironmental proxies and the unprecedented breadth of sampling and depth of taxonomic analyses provided by the Panama Paleontology Project (PPP). Three hypotheses will be tested: (1) Doomed taxa survived in nutrient-rich refugia that persisted after Isthmus closure; extinction occurred when refugia diminished sufficiently. (2) Extinction was driven by cooling related to northern hemisphere glaciation. (3) Temporary survival of doomed taxa was unrelated to changes in nutrients or temperature, suggesting stochastic processes were responsible. To accomplish this, we will generate high-resolution stable isotopic (18O/16O, 13C/12C) profiles of ~90 gastropod shells from 26 fossil localities in the SWC dating between 5 and 1.4 Ma, supplemented by clumped isotope (13C18O/12C16O) and trace element (P/Ca, Sr/Ca, Ba/Ca) analyses, to determine past local temperature and nutrient availability. This project will be the first to establish a well-constrained environmental system using the Tropical American fossil record and multiple high-resolution geochemical proxies to test a range of evolutionary hypotheses. These include the processes responsible for speciation, extinction, niche expansion, and evolutionary maintenance of sexual reproduction. Uniting biotic data with detailed paleoenvironmental data will reveal the root cause of the most geologically recent marine extinction and provide a real-world example with which to test models of the process of large-scale biodiversity loss. The modern anthropogenic fragmentation of natural habitats and populations mirrors the refugia that are purported to have delayed the extinction of SWC taxa in the Pliocene. Our data will evaluate this hypothesis and demonstrate whether this loss in biodiversity was directly related to environmental changes.The project will integrate a Panama-based field experience into the undergraduate capstone course of the Environmental Programs in Geoscience at Texas A&M University (TAMU). Students will work in groups and conduct paleobiology and stable isotope research on samples they collect in Panama, and sample and analyze at TAMU. In addition to presenting results, students will write, peer-review, and revise research papers. The project will train a post-doctoral fellow and graduate student in interdisciplinary science and research mentoring. Finally, research findings will be presented at major national and international meetings and published in premier journals.