Relevance of Planktonic Larval Dispersal to Endemism and Biogeography of Antarctic Benthic Invertebrates

Because of extreme isolation of the Antarctic continent since the Early Oligocene, one expects a unique invertebrate benthic fauna with a high degree of endemism. Yet some invertebrate taxa that constitute important ecological components of sedimentary benthic communities include more than 40 percent non-endemic species (e.g., benthic polychaetes). To account for non-endemic species, intermittent genetic exchange must occur between Antarctic and other (e.g. South American) populations. The most likely mechanism for such gene flow, at least for in-faunal and mobile macrobenthos, is dispersal of planktonic larvae across the sub- Antarctic and Antarctic polar fronts. To test for larval dispersal as a mechanism of maintaining genetic continuity across polar fronts, the scientists propose to (1) take plankton samples along transects across Drake passage during both the austral summer and winter seasons while concurrently collecting the appropriate hydrographic data. Such data will help elucidate the hydrographic mechanisms that allow dispersal across Drake Passage. Using a molecular phylogenetic approach, they will (2) compare seemingly identical adult forms from Antarctic and South America continents to identify genetic breaks, historical gene flow, and control for the presence of cryptic species. (3) Similar molecular tools will be used to relate planktonic larvae to their adult forms. Through this procedure, they propose to link the larval forms respectively to their Antarctic or South America origins. The proposed work builds on previous research that provides the basis for this effort to develop a synthetic understanding of historical gene flow and present day dispersal mechanism in South American/Drake Passage/Antarctic Peninsular region. Furthermore, this work represents one of the first attempts to examine recent gene flow in Antarctic benthic invertebrates. Graduate students and a postdoctoral fellow will be trained during this research.自渐新世早期（Early Oligocene）以来，南极大陆便长期处于极度隔离的状态，因此学界普遍推测其拥有特有性极高的独特无脊椎底栖动物群（invertebrate benthic fauna）。然而，构成沉积底栖群落（sedimentary benthic communities）重要生态组分的部分无脊椎动物类群中，非特有种占比超过40%，例如底栖多毛类（benthic polychaetes）。为解释这类非特有种的成因，南极与其他区域（如南美洲）的种群之间必然存在间歇性的基因交流。这类基因交流最可能的发生机制，至少针对底内生物（in-faunal）与移动型大型底栖生物（mobile macrobenthos）而言，是浮游幼虫（planktonic larvae）跨越亚南极（sub-Antarctic）与南极极锋（polar fronts）进行扩散。 为验证浮游幼虫扩散是否为维持极锋两侧遗传连续性的核心机制，研究者计划开展以下工作：(1) 在南半球夏季与冬季，沿横穿德雷克海峡（Drake Passage）的断面采集浮游生物样本，并同步收集配套的水文数据（hydrographic data）。此类数据将有助于阐明支撑跨德雷克海峡扩散的水文调控机制。(2) 采用分子系统发育学方法（molecular phylogenetic approach），对比采自南极与南美洲大陆的形态相似成体样本，以识别遗传分化断点（genetic breaks）、历史基因流情况，并校正隐存种（cryptic species）的存在。(3) 利用同类分子生物学工具，将浮游幼虫与其对应成体进行关联匹配。通过该研究流程，研究者旨在明确各幼虫样本分别源自南极还是南美洲种群。 本研究计划建立在前期相关研究的基础之上，这些前期成果为综合解析南美洲/德雷克海峡/南极半岛（Antarctic Peninsular）区域的历史基因流与当代扩散机制提供了重要依托。此外，本研究亦是首批针对南极底栖无脊椎动物近期基因流开展系统性探究的尝试之一。本研究期间将培养多名研究生与一名博士后研究人员。