Collaborative research, SG, RUI: The importance of the X-chromosomes in speciation: are genes that do not introgress concentrated on the X chromosome?

为了了解新物种是如何进化的，我们需要了解参与这一过程的基因，以及这些基因在基因组中的位置。物种形成源于导致个体群体间生殖不相容的基因，早期的研究表明这些基因位于X染色体上。该项目将研究X染色体在两种密切相关的蟋蟀物种进化中的作用。这两种蟋蟀仍然能够产生一些杂交后代并交换遗传信息。这些物种的种群共同出现在美国东北部，在那里它们形成了一个广泛的自然杂交区，在那里基因已经交换了数千代。研究人员将调查物种之间的基因混合率，并确定它在基因组中的位置。这项研究将通过测试X染色体是否显示物种之间的遗传交换率较低，来解决X染色体包含导致生殖隔离的基因的假设。位于低基因交换区域内的特定基因也将被识别出来，以进一步了解新物种进化所需的条件。这是一个合作研究项目，将主要在文科本科学院进行，并将提供大量的机会来培训和指导本科生。推广活动包括科学教育研讨会和活动，并将针对STEM领域代表性不足的初中和高中学生。拟议的研究将测试X染色体在物种形成中的重要性，以及在野外蟋蟀（灰蟋蟀和宾夕法尼亚蟋蟀）中观察到的分化岛是否反映了差异的渗入和/或最近的选择。该项目有三个主要目标。首先，将利用杂交回交和物种内杂交来绘制X染色体；这些x连锁染色体标记的分化模式将被评估。其次，基因序列将从显示不同物种之间基因交换和分化率的基因组区域获得。基因流动率低、分化率高的基因组区域可能包含负责生殖隔离和物种特性的基因。将对高分化区和低分化控制区计算遗传分化的绝对和相对度量和选择估计。这些结果将用于测试基因组是否由高低分化区域拼凑而成。第三个目标是基于对两种蟋蟀之间存在单向不相容的观察，但这一“规则”在某些种群杂交中被打破。如果高分化区域是造成生殖隔离的原因，那么在生育后代和不生育后代的配对之间应该存在一致的基因组差异。结果将为物种形成的基因组结构、X染色体在生殖隔离和分化适应中的作用提供重要见解，并将有助于正在进行的关于基因组分化岛的辩论。

To understand how new species evolve we need to understand the genes involved in the process and where these genes are located in the genome. Speciation results from genes that cause reproductive incompatibilities between groups of individuals, and earlier studies have suggested these genes are located on the X chromosome. This project will investigate the role of the X chromosome in the evolution of two closely related species of field crickets. These two cricket species are still capable of producing some hybrid offspring and exchanging genetic information. Populations of these species co-occur in the Northeastern U.S., where they form an extensive natural hybrid zone, in which genes have been exchanged for thousands of generations. The researchers will investigate rates of genetic mixing between the species, and determine where it occurs across the genome. This research will address the hypothesis that the X chromosome contains the genes that lead to reproductive isolation, by testing whether the X chromosome shows a lower rate of genetic exchange between species. Specific genes located within regions of low genetic exchange will also be identified to further our understanding of what is required for new species to evolve. This is a collaborative research project that will be mainly conducted at a liberal arts, undergraduate college and will provide substantial opportunity for training and mentoring of undergraduate students. Outreach includes science education workshops and activities, and will target underrepresented, middle and high school students in STEM fields. The proposed research will test both the importance of the X chromosome in speciation and whether observed islands of differentiation in the field crickets, Gryllus firmus and G. pennsylvanicus, reflect differential introgression and/or recent selection. The project has three main objectives. First, the X chromosome will be mapped using hybrid backcrosses and within species crosses; patterns of differentiation for these X-linked chromosome markers will be assessed. Second, gene sequences will be obtained from genome regions that show varying rates of gene exchange and differentiation between species. Genome regions with low rates of gene flow and high differentiation might harbor genes responsible for reproductive isolation and species identities. Absolute and relative measures of genetic differentiation and estimates of selection will be calculated for high differentiation regions and for control regions with low differentiation. These results will be used to test if the genome is composed of a patchwork of high and low differentiation regions. The third objective is based on the observation that there is a one-way incompatibility between the two cricket species, but that this 'rule' is broken in some population crosses. If regions of high differentiation are responsible for reproductive isolation, then there should be consistent genomic differences between pairs that produce offspring and those that do not. Results will provide important insights into the genomic architecture of speciation, the role of the X chromosome in reproductive isolation and divergent adaptation, and will contribute to ongoing debates about genomic islands of differentiation.