Marine Biotech Fellowship: The Population Genetic Consequences of Histocompatibility in a Colonial Ascidian

控制同种异体识别的基因在脊椎动物和无脊椎动物中都可以是高度多态性的。本项目将研究一些可能在一个模式系统中启动和维持这种多态性的选择力，即殖民地海鞘，Botryllus schlosseri。在这种海鞘中，一个高度多态的异体识别位点似乎控制着群体融合和配子不相容的过程。有人认为，一种精确的异体识别系统可能已经在Schlosseri中进化出来，以降低与群体融合相关的体细胞寄生的成本和/或降低近亲繁殖的水平，如果男性生育能力是精子浓度的简单功能，则预期。这个项目将通过提出以下具体问题来检验这些想法：1)群体融合的遗传成本是什么？2)自然种群中基因嵌合体的频率是多少？3)配子不亲和性在多大程度上降低了近亲交配中的雄性育性？为了回答这些问题，研究将：首先，通过DNA指纹图谱确定探针和限制性内切酶的最佳组合；其次，从基因上描述融合菌落的组织和种系随时间变化的特征；第三，对随机取样的群体的组织和后代进行基因分类，以确定由基因嵌合体组成的当地群体的百分比；第四，该项目将利用精子竞争实验和近亲交配中父系受精的成功。这个项目将提供两种产品。第一个产品将是组织相容性的遗传后果的描述。这些信息对于我们理解克隆海洋无脊椎动物群落中群体融合和配子不相容的适应性意义，以及识别启动和维持高水平同种异体多态性的选择力至关重要，这是精确的同种异体识别系统所必需的。第二个产品将是用于估计亲子关系的分子技术的发展。在未来，这种能力将允许进行更详细的遗传研究，试图重建种群的谱系，并评估不同基因型的进化适应性。

The genes governing allorecognition in both vertebrates and invertebrates can be highly polymorphic. This project will examine some of the selective forces that may have initiated and maintained this polymorphism in a model system, the colonial ascidian, Botryllus schlosseri. In this ascidian, a single and highly polymorphic allorecognition locus appears to govern the processes of colony fusion and gamete incompatibility. It is argued that a precise allorecognition system may have evolved in B. Schlosseri to reduce the costs of somatic cell parasitism associated with colony fusion and/or to decrease the level of inbreeding over that expected if male fertilities were a simple function of sperm concentration. This project will test these ideas by asking the following specific questions: 1) What are the genetic costs of colony fusion? 2) What is the frequency of genetic chimeras in natural populations? and 3) To what extent does gametic incompatibility lower male fertilities in matings among kin? To answer these questions the research will: first, determine the best combination of probes and restriction enzymes for the genetic typing of individuals by DNA fingerprinting; second, genetically characterize what happens to the tissues and germ lines of fused colonies over time; third, genetically type the tissues and progeny of a random sample of colonies to determine what percentage of a local population consists of genetic chimeras; and fourth, the project will use sperm competition experiments and paternity fertilization success in matings among kin. This project will provide two products. The first product will be a description of the genetic consequences of histocompatibility. Such information will be critical to our understanding of the adaptive significance of colony fusion and gamete incompatibility in communities of clonal marine invertebrates as well as for identifying the selective forces that initiated and maintained the high levels of allotypic polymorphism that are necessary for a precise allorecognition system. The second product will be the development of molecular techniques for the estimation of paternity. In the future, this capability will allow for more detailed genetic studies that attempt to reconstruct the genealogy of populations and assess the evolutionary fitness of different genotypes.