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

赤道附近的温暖海水和强劲洋流使北方和南半球的海洋群落保持着明显的区别。然而，许多分类群已经建立了“反热带”分布，出现在热带两侧的温带，但不在最温暖的热带地区。虽然古生物学研究和分子生物学提供了关于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，可以开始调查关于北方和南半球之间生物连通性的最近历史和未来前景的几个基本问题。该项目的重点是在反热带的鹅颈藤壶Polles elegans在整个热带地区的连接特性。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沃茨却没有。先前收集的数据表明，mtDNA单倍型谱系在北方和南半球人群之间是共享的，并且南北之间的分离相对较近，在过去的16万年内。这项研究有两个主要目标。首先，研究人员将使用多位点序列数据和微卫星位点来估计北方和南方种群分离的时间，以及自分裂以来发生了多少基因流动，无论是在进化时间尺度上还是在最近几代人中。第二个目标是表征幼虫的热耐受性和性能作为一种手段来测试的假设，温度是一个障碍，幼虫分散在最温暖的热带地区的P.秀丽隐杆线虫。虽然其他几种假设可以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提供第一个重要的生理测试温度如何限制连通性。了解基因流的历史和分散幼虫的温度耐受性将提供洞察热带海洋表面温度的最近和预计的增加对最近和未来的半球之间的连接模式的影响。该项目将为两名研究生和两名博士后研究人员提供实地考察，种群遗传学和幼虫生态学方面的财政支持和培训。本科生将通过在分子种群生物学教授的动手实验室课程和从克莱姆森教授的课程招聘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（LaFrance，南卡罗来纳州）进行接触。研究人员积极发表在领先的科学期刊和书面邀请贡献的领域的地理和生活史进化。他们实验室的研究通过网页传播，以前的工作已经通过各种各样的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.