Understanding of diachroneity: Palaeoenvironmental controls on dispersal of planktic foraminifera in the Plio-Pleistocene oceans

宏观进化是物种的产生、繁殖和消失。大多数海洋物种缺乏物理屏障和种群规模大，应允许在物种形成后新栖息地的迅速扩散和殖民。然而，基因流动似乎比我们基于这一分析所预测的要有限：许多浮游有孔虫物种在海洋盆地之间和内部的历时首次出现日期表明，种群的建立往往在物种形成后立即受到临时限制。最近的研究表明，即使是在一个世界性的海洋硅藻物种中，基因的流动也在海洋盆地的规模上受到限制。这些观察表明，(1)在公海扩散的物理障碍比通常所援引的更强，(2)这些障碍的特性及其工作机制知之甚少。这项拟议的研究将利用2019年5月至7月国际海洋发现计划(IODP)383次考察期间发现的深海沉积物中的上更新世浮游有孔虫，研究环南极开阔海洋中扩散动力学的环境驱动因素。被点名的研究员Anieke Brombacher博士作为英国IODP赞助的科学家，作为浮游有孔虫生物地层学家参加了383次远征。浮游有孔虫非常适合于深入分析时间扩散动力学，因为它们在海洋沉积物中的高分辨率化石记录允许重建跨空间和跨时间的种群动态。利用IODP探险383号回收的沉积物，我们将研究亚极地南太平洋的物种扩散和迁徙，该区域通过德雷克海峡连接太平洋和大西洋，但位于许多物种地理范围的边缘。383探险队在南极前锋以北的六个南太平洋地点进行了钻探，这些地点非常适合产生不受主要冰筏干扰的极高分辨率的沉积物记录。我们将记录其中三个地点的有孔虫演化，并将这些记录与南极绕极流(ACC)变异性的地球化学重建进行比较。具体地说，从IODP站点U1539、U1540和U1541恢复的高分辨率上新世-更新世沉积物档案将用于研究通过Drake Passage的边缘种群扩散，Drake Passage是连接太平洋和大西洋的关键高纬度海洋门户，响应40 KYR冰川周期。尽管德雷克海峡形成了一条明显的潜在迁徙路线，但在热带至中纬度太平洋首次出现后，直到0.5-1.0Myr，才出现在大西洋中。这一观察表明，在温带水物种进化历史的早期，高纬度地区对它们的扩散构成了环境障碍。IODP383个站点U1539-U1541的初步船上结果显示，在冰期-间冰期旋回中，组合组成不同。这些站点都位于西南太平洋S度55度左右。冰川组合以极地物种厚皮新球藻为主，但间冰期组合含有更多温带物种，包括各种Truncorotalia和Globoconella类群。这些初步发现表明，间冰期可能会削弱扩散到更高纬度的障碍，并促进那里的适应，这一机制类似于“岛屿希望”。为了验证这一工作假设，需要高分辨率的物种计数、形态测量和稳定的同位素数据，以确定适应情况是否随着连续间冰期的海洋条件而改善。

Macroevolution is the generation, proliferation and removal of species. The lack of physical barriers and large population size of most marine species should allow for rapid dispersal and colonization of new habitats following speciation. However, gene flow appears more limited than we would predict based on this analysis: diachronous first occurrence dates among and within ocean basins of many species of planktonic foraminifera suggest that population establishment is often temporarily restricted immediately after speciation. Recent work shows that even in a cosmopolitan marine diatom species, gene flow is restricted at an ocean basin scale. These observations indicate that (i) physical barriers to dispersion in the open ocean are stronger than commonly invoked and (ii) the identity of these barriers and their working mechanisms are poorly understood. The proposed research will study environmental drivers of dispersal dynamics in the open ocean of the circum- Antarctic using planktonic foraminifera of Plio-Pleistocene age in deep sea sediments recovered during International Ocean Discovery Program (IODP) Expedition 383 in May-July 2019. The named researcher, Dr Anieke Brombacher, participated in Expedition 383 shipboard as a planktonic foraminifer biostratigrapher as a UK-IODP sponsored scientist.Planktonic foraminifera are ideally suited for in-depth analysis of temporal dispersal dynamics because their high-resolution fossil record in marine sediments allows for reconstructions of population dynamics across space and through time. Using sediments recovered by IODP Expedition 383, we will study species dispersal and migration in the sub-polar Southern Pacific Ocean, a region that, via the Drake Passage, connects the Pacific and Atlantic Oceans but lies at the edge of many species' geographical ranges. Expedition 383 drilled six South Pacific sites well north of the Antarctic front, that are well-suited to producing extremely high-resolution sediment records undisturbed by major ice rafting. We will document foraminifera evolution at three of these sites and compare those records to geochemical reconstructions of variability in the Antarctic Circumpolar Current (ACC). Specifically, high-resolution Pliocene-Pleistocene sediment archives recovered from IODP Sites U1539, U1540 and U1541 will be used to study edge population dispersal through Drake Passage, a key high latitude ocean gateway connecting the Pacific and Atlantic Oceans in response to 40-kyr glacial cycles.The Neogene planktonic foraminifera species Truncorotalia truncatulinoides, Globoconella puncticulata puncticuloides and Globoconella inflata all originated in the Southwest Pacific Ocean. However, G. puncticulata puncticuloides has not been recorded in any other ocean basin, and T. truncatulinoides and G. inflata do not appear in the Atlantic Ocean until 0.5-1.0 Myr after their first appearance in the tropical to mid-latitude Pacific despite the Drake Passage forming an obvious potential migration route. This observation suggests that the high latitudes presented an environmental barrier to the dispersal of temperate-water species early in their evolutionary history. Initial shipboard results from IODP 383 Sites U1539 - U1541, all located around 55 degrees S in the SW Pacific, show varying assemblage compositions across glacial-interglacial cycles. Glacial assemblages are dominated by the polar species Neogloboquadrina pachyderma but interglacial assemblages contain more temperate species including various Truncorotalia and Globoconella taxa. These initial findings suggest that interglacials potentially act to weaken barriers to dispersal to higher latitudes and facilitate adaptation there, a mechanism akin to 'island hoping'. To test this working hypothesis, high-resolution species counts, morphometric and stable isotope data are required to determine whether adaptation improves with exposure to ocean conditions in successive interglacials.