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，需要更好地理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)的上更新世灭绝事件(1-2 Myr)，以研究环境扰动与灭绝速率之间的关系。在上更新世事件期间，加勒比海各种海洋类群的灭绝速度达到了35%到100%的峰值。更好地适应营养丰富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，由于与太平洋隔绝，加勒比水域的浮游生物营养物质减少。然而，物种灭绝滞后于闭幕1-2迈尔，导致一些研究人员将灭绝速度的增加归因于与北半球冰川开始相关的气候变化。这项研究将综合生物和地球化学数据，以揭示加勒比物种灭绝事件的直接原因，并利用已建立的和新的古环境指标以及巴拿马古生物学项目提供的前所未有的采样和分类分析的广度来评估所察觉到的延迟的证据。将检验三个假设：(1)注定要灭绝的类群在地峡关闭后持续存在的营养丰富的避难所中存活；当避难所足够减少时，灭绝发生。(2)与北半球冰川作用相关的降温作用驱动了物种灭绝。(3)濒临死亡的类群的暂时存活与营养物质或温度的变化无关，表明随机过程起了作用。为了实现这一目标，我们将生成来自SWC 26个化石地点的~90个腹足类贝壳的高分辨率稳定同位素(18O/16O，13C/12C)剖面，年龄在5 Ma到1.4 Ma之间，并辅之以块状同位素(13C18O/12C16O)和微量元素(P/Ca，Sr/Ca，Ba/Ca)分析，以确定过去当地的温度和养分有效性。这个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指标来测试一系列进化假说的受良好约束的环境系统。这些过程包括物种形成、灭绝、生态位扩张和有性繁殖的进化维持。将生物数据与详细的古环境数据结合起来，将揭示最近一次地质上的海洋灭绝的根本原因，并提供一个真实世界的例子，用来检验大规模生物多样性丧失过程的模型。现代人类对自然栖息地和种群的碎片化反映了避难所，据称这种避难所推迟了上新世SWC分类群的灭绝。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峰课程中。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进行样本和分析。除了报告结果外，学生还将撰写、同行评议和修改研究论文。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研究生。最后，研究成果将在重要的国内和国际会议上发表，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.