Gene Flow and Divergence Across the Equatorial Tropical Marine Barrier: Past, Present and Future

北半球和南半球的海洋群落因赤道附近的温暖海水和强劲洋流而保持不同。然而，许多类群已经建立了“反热带”分布，出现在热带两侧的温带地区，但不在最温暖的热带地区。尽管古生物学研究和分子系统发育提供了有关跨热带殖民的时间和方向的信息，但具有反热带分布的单一物种的存在提供了一个机会来开始研究有关南北半球之间生物连通性的近期历史和未来前景的几个基本问​​题。该项目的重点是表征逆热带鹅颈藤壶 Pollicipes elegans 跨热带地区的连通性。这种东太平洋物种在两个半球都有发现，但在赤道以北最温暖的水域中却没有。先前收集的数据显示，北半球和南半球人群共享 mtDNA 单倍型谱系，而且南北半球之间的分离相对较新，是在过去 16 万年内。 This research has two main goals.首先，研究人员将使用多基因座序列数据和微卫星基因座来估计北部和南部种群分离的时间，以及自分离以来在进化时间尺度上和最近几代中发生了多少基因流。第二个目标是表征幼虫的耐热性和性能，作为检验温度是线虫幼虫在最温暖的热带地区传播的障碍这一假设的手段。尽管其他几个假设可以潜在地解释是什么使秀丽隐杆线虫远离热带，例如赤道边界流或定居后过程的隔离效应，但评估分散幼虫阶段的温度敏感性将为温度如何限制连通性提供第一个重要的生理测试。了解基因流的历史和分散幼虫的温度耐受性将有助于深入了解最近和预计的热带海洋表面温度上升对近期和未来半球之间连通模式的影响。该项目将为两名研究生和两名博士后研究人员提供现场工作、群体遗传学和幼虫生态学方面的财政支持和培训。本科生将通过分子群体生物学教授的实践实验室课程以及克莱姆森教授课程的招募来参与研究的各个方面。研究人员还将继续通过科学家（PI、研究生和博士后）的课堂访问与当地学区（南卡罗来纳州拉弗朗斯）进行接触。研究人员在领先的科学期刊上积极发表文章，并为生物地理学和生命史进化领域撰写了受邀稿件。他们实验室的研究通过网页传播，之前的工作也通过各种媒体渠道向公众传播。

The marine communities of the northern and southern hemispheres are kept distinct by warm water and strong currents near the equator. Nevertheless, many taxa have established "antitropical" distributions, occurring in temperate zones on either side of the tropics but not within the warmest tropical regions. Although paleontological studies and molecular phylogenies provide information about the timing and direction of trans-tropical colonization, the existence of single species with antitropical distributions provides an opportunity to begin to investigate several fundamental questions about the recent history of and future prospects for biological connectivity between the northern and southern hemispheres. This project focuses on characterizing connectivity across the tropics in the antitropical gooseneck barnacle Pollicipes elegans. This eastern Pacific species is found in both hemispheres but is absent from the warmest waters immediately to the north of the equator. Previously-collected data show that mtDNA haplotype lineages are shared between northern and southern hemisphere populations, and that the separation between north and south has been relatively recent, within the last 160,000 years. This research has two main goals. First, the investigators will use multi-locus sequence data and microsatellite loci to estimate the time of separation of northern and southern populations and how much gene flow has occurred since that split, both over evolutionary timescales and across recent generations. The second goal is to characterize larval thermal tolerance and performance as a means to test the hypothesis that temperature is a barrier to larval dispersal across the warmest tropical regions in P. elegans. Although several other hypotheses can potentially explain what keeps P. elegans out of the tropics, such as the isolating effects of the equatorial boundary currents or post-settlement processes, assessing the temperature sensitivity of the dispersive larval stage will provide the first important physiological test of how temperature limits connectivity. Understanding the history of gene flow and the temperature tolerance of dispersive larvae will provide insight into the impacts of recent and projected increases in tropical sea surface temperatures on recent and future patterns of connectivity between the hemispheres.This project will provide financial support and training in fieldwork, population genetics, and larval ecology for two graduate students and two postdoctoral researchers. Undergraduate students will be involved with aspects of the research through a hands-on lab class taught in Molecular Population Biology and recruitment from courses taught at Clemson. The investigators will also continue to engage a local school district (LaFrance, South Carolina) via classroom visits by scientists (PI, graduate students, and postdocs). The investigators publish actively in leading scientific journals and written invited contributions for the fields of biogeography and life history evolution. Research in the their labs is disseminated via web pages and previous work has reached the public through a wide variety of media outlets.