DISSERTATION RESEARCH: Identifying the genetic basis of adaptation to a freshwater environment using admixture in natural populations

这项研究将确定使大西洋千里鱼从咸水迁移到淡水的基因变化。适应不同的环境对于产生生物多样性很重要，对于鱼类来说，环境盐度是限制它们能在哪里生活的一个主要因素。因此，对不同盐度的适应被认为是鱼类惊人生物多样性产生的关键。然而，人们对使物种能够适应不同盐度的遗传和生理变化知之甚少。大西洋剑鱼主要生活在海洋栖息地，但一些种群最近转移到了淡水中。淡水种群为发现使生活在淡水环境中的生命得以发生的基因变化提供了理想的研究系统。这项研究很重要，因为它将阐明进化变化的类型，这些变化允许该物种，也许还有许多物种，在新的环境中定居，导致鱼类的生物多样性。通过对本科生进行项目技术和研究方法的培训，该项目将产生更广泛的社会影响。此外，这项研究将通过加州大学戴维斯分校的AggieMentors计划为弱势青年的大学预备辅导提供材料。本研究的主要目的是确定与低盐度耐受性相关的遗传位点。混合作图是一种利用遗传和表型不同群体之间的自然杂交来确定影响特定表型性状的基因座的方法。混合测绘将应用于两个重复的杂交区：一个在切萨皮克湾由淡水原住民和微咸水原住民组成，另一个沿东海岸，那里的北部和南部人口都是海洋的。在这些区域进行采样将提供基因相似的种群，而这些种群面临着截然不同的选择压力。因此，有可能弄清遗传祖先的影响与选择对适应低盐度环境的鱼类适应性的影响。将对亲本群体及其杂交后代进行低盐耐受性测试，并使用限制性内切酶位点相关遗传标记进行基因分型。混合作图将确定影响特定表型的基因座。全基因组分析将确定仅在淡水环境中选择的基因座。这一组合不仅可以识别与一般耐盐性有关的表型，而且还将揭示那些驱动最近适应淡水的基因座。

This research will determine the genetic changes that have permitted the Atlantic killifish, Fundulus heteroclitus, to move from saltwater to freshwater. Adaptation to different environments is important for generating biological diversity, and for fish, environmental salinity is a major factor limiting where they can live. Adaptation to different salinities is therefore thought to have been critical in the generation of the amazing biodiversity of fishes. However little is known about the genetic and physiological changes that enable species to adapt to different salinities. The Atlantic killifish mainly occupies marine habitats, but some populations have recently moved into fresh water. The freshwater populations provide an ideal study system for discovering the genetic changes that have enabled life in a fresh water environment. This research is important because it will shed light on the types of evolutionary changes that have permitted this species, and perhaps many species, to colonize new environments resulting in the biodiversity of the fishes. The project will have broader societal impacts through the training of undergraduates in the techniques and research methodology of the project. In addition, the research will provide material in college preparatory mentorship of disadvantaged youth through the AggieMentors program at UC Davis. The main goal of this research is to identify the genetic loci that are associated with tolerance of low salinity. Admixture mapping is a method that takes advantage of natural hybridization between genetically and phenotypically distinct populations in order to determine the loci that influence a particular phenotypic trait. Admixture mapping will be applied to two replicate hybrid zones: one within the Chesapeake Bay consisting of a freshwater native and a brackish water native population, and the other along the east coast where a northern and southern population are both marine. Sampling in these zones will provide genetically similar populations that experience vastly different selective pressures. It is therefore possible to disentangle the effects of genetic ancestry versus the effects of selection on the fitness of fish adapted to low salinity environments. Parental populations and their hybrids will be tested for low salinity tolerance and genotyped using restriction site associated genetic markers. Admixture mapping will identify loci contributing to the specific phenotypes. Genome-wide analysis will identify loci that are under selection only in the freshwater environment. This combination will not only allow for the identification of phenotypes involved in general salinity tolerance, but also will reveal those loci driving recent adaptation to fresh water.