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、增殖和迁移。由于大多数海洋物种没有物理屏障，而且种群数量庞大，因此在物种形成后，它们可以迅速扩散并定居到新的生境。然而，基因流似乎更有限，我们会预测基于这种分析：穿时的第一次发生日期之间和海洋盆地内的许多物种的浮游有孔虫表明，人口的建立往往是暂时限制后立即形成。最近的工作表明，即使在一个世界性的海洋硅藻物种，基因流是有限的，在海洋盆地规模。这些观察结果表明，㈠在公海扩散的物理障碍比通常所说的更强，㈡对这些障碍的特性及其工作机制知之甚少。拟议的研究将研究环南极开放海洋中扩散动力学的环境驱动因素，使用2019年5月至7月国际海洋发现计划（IODP）第383次考察期间回收的深海沉积物中上新世-更新世时代的浮游有孔虫。被命名的研究员Anieke Brombacher博士作为UK-IODP赞助的科学家作为浮游有孔虫生物地层学家参加了383号考察船。浮游有孔虫非常适合深入分析时间扩散动态，因为它们在海洋沉积物中的高分辨率化石记录可以重建空间和时间上的种群动态。使用IODP远征383恢复的沉积物，我们将研究亚极地南太平洋的物种扩散和迁移，该地区通过德雷克海峡连接太平洋和大西洋，但位于许多物种的地理范围的边缘。第383号考察队在南极锋面以北的六个南太平洋地点进行了钻探，这些地点非常适合制作不受主要冰漂流影响的极高分辨率沉积物记录。我们将记录有孔虫的进化在这些网站中的三个，并比较这些记录在南极绕极流（ACC）的变化的地球化学重建。具体而言，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德雷克通道的边缘种群扩散，德雷克通道是连接太平洋和大西洋的一个关键高纬度海洋门户，对40 kyr冰川周期作出反应。点状球锥虫和膨胀球锥虫均起源于西南太平洋。然而，G. puncticulata puncticuloides在其他海盆中未见报道，T. truncatulinoides和G.尽管德雷克海峡形成了一条明显的潜在迁移路线，但直到0.5-1.0百万年后，它们才首次出现在大西洋的热带至中纬度太平洋。这一观察结果表明，高纬度地区在其进化史的早期就对温水物种的扩散构成了环境障碍。来自IODP 383站点U1539 - U1541的初始船上结果，都位于西南太平洋南纬55度附近，显示了不同的冰川-间冰期循环组合成分。冰川组合以极地种Neogloboquadrina pachyderma为主，但间冰期组合包含更多的温带种，包括各种Truncorotalia和Globoconella类群。这些初步研究结果表明，间冰期可能会削弱向高纬度地区扩散的障碍，并促进那里的适应，这是一种类似于“岛屿希望”的机制。为了检验这一工作假设，需要高分辨率的物种计数、形态测量和稳定同位素数据，以确定在连续的间冰期中，适应性是否随着暴露于海洋条件而改善。

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.