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碎片化将导致未来很长一段时间内的物种灭绝——这一过程被称为“灭绝债务”——但要做出准确的预测，需要更好地了解物种灭绝是如何在长期时间尺度上发生的。本项目将剖析加勒比海西南部（SWC）的上新世-更新世灭绝事件（1- 2myr），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，加勒比地区各种海洋分类群的灭绝率在35%到100%之间达到顶峰。适应营养丰富条件的分类群受到的影响最大。因此，这种灭绝通常被归因于中美洲地峡关闭后加勒比水域与太平洋隔绝，从而导致加勒比海水域浮游生物营养物质减少。然而，物种灭绝滞后于1-2兆尔，导致一些研究人员将物种灭绝率的增加归因于与北半球冰川作用开始相关的气候变化。本研究将整合生物和地球化学数据，揭示加勒比地区灭绝事件的直接原因，并利用现有的和新的古环境代用指标，以及巴拿马古生物学项目（PPP）提供的前所未有的采样广度和分类分析深度，评估可感知的延迟证据。三种假设将被检验：(1)注定灭亡的类群在地峡关闭后持续存在的营养丰富的避难所中幸存下来；当避难所减少到一定程度时，灭绝就发生了。(2)与北半球冰川作用相关的变冷驱动了物种灭绝。(3)灭亡类群的暂时生存与营养物质和温度变化无关，可能与随机过程有关。为了实现这一目标，我们将在SWC的26个化石地点生成高分辨率稳定同位素（18O/16O, 13C/12C）剖面，并补充块状同位素（13C18O/12C16O）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有效性。该项目将是第一个利用热带美洲化石记录和多种高分辨率地球化学代理来测试一系列进化假设的良好约束环境系统。这些过程包括物种形成、灭绝、生态位扩展和有性生殖的进化维持。将生物数据与详细的古环境数据结合起来，将揭示地质上最近一次海洋灭绝的根本原因，并提供一个真实世界的例子，用于测试大规模生物多样性丧失过程的模型。现代自然栖息地和种群的人为破碎反映了据称推迟了上新世SWC分类群灭绝的避难所。我们的数据将评估这一假设，并证明这种生物多样性的丧失是否与环境变化直接相关。该项目将把巴拿马的实地经验整合到德克萨斯农工大学（TAMU）地球科学环境项目的本科顶点课程中。学生们将分组工作，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进行取样和分析。除了展示成果外，学生还将撰写、同行评审和修改研究论文。该项目将培养一名跨学科科学和研究指导方面的博士后和研究生。最后，研究成果将在主要的国家和国际会议上发表，并在主要期刊上发表。

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.