BE/GenEn: A Biochemical, Genetic, and Genomic Investigation of the Evolution and Ecology of Sexual Reproduction

有性生殖在植物和动物中广泛存在，但人们对其选择优势知之甚少。有性生殖产生的基因重组强烈地影响着进化速率、基因组结构和适应性，然而关于基因和生态系统如何相互作用以维持有性生殖并决定其频率，我们知之甚少。在许多物种中，突变或杂交产生无性繁殖的种群。然而，大多数物种和几乎所有高阶分类群都维持有性繁殖，这意味着性的进化丧失最终会导致灭绝。这种矛盾在既能有性繁殖又能无性繁殖的物种中尤为突出。在这些物种中，大多数繁殖是无性的，但环境因素会引发偶发性的有性繁殖。尽管在这些物种中，性很容易丧失，但在进化过程中，无性繁殖和有性繁殖都得以维持。因此，无性/有性物种是研究无性和有性繁殖、环境和物种进化的动态相互作用的一个特别强大的系统。对性动力学的理解至关重要的是基因的进化和生态作用，这些基因决定了种群中有性繁殖的频率和流行程度。最终，这些基因影响着遗传多样性、适应和物种形成的速度以及生态系统中生物复杂性的水平。尽管这些基因很重要，但在动物身上发现的这些基因很少，它们的进化动力学在很大程度上仍然未知。本研究的目的是在轮虫这个最大、最成功的无性/有性动物群体中分离和表征这些基因，并跟踪这些基因与基因组和环境的进化和功能相互作用，以了解基因和环境如何相互作用来调节有性生殖和确定其频率。该项目将采用生物化学、遗传学和数学方法相结合的方法，包括蛋白质纯化和功能分析、基因文库分析，以及通过比较失去有性繁殖能力的自然种群和实验室种群来确定调节途径。在这个为期一年的探索性项目中，三个目标中的第一个是完成轮虫性诱导蛋白（MIP）的蛋白质纯化。二是获得MIP和轮虫配偶识别信息素（MRP）的氨基酸序列，从而推断出基因的核苷酸序列。第三个目标是通过筛选轮虫有性繁殖种群的cDNA基因库来分离MRP和MIP基因。最终，这些测量将阐明生命周期中维持有性生殖的力量，实验室和自然种群中有性生殖丧失的动态，这种丧失的潜在遗传机制，并建立与可能影响这些过程的环境变量的相关性。将开发模型来解释和预测性别比、性诱导阈值，并确定预期会丧失有性生殖的环境。该项目将为1名研究技术人员和2名本科生提供跨学科研究培训。将维持一个具有良好特征的轮虫库，并应要求分发样品。该项目将扩展一个网站（jbpc.mbl.edu/wheelbase），提供一个可搜索的基因文库、实验结果和技术描述的数据库。这些工具和资源将使许多研究人员能够将轮虫纳入比较遗传研究。

Sexual reproduction is widespread among plants and animals, but its selective advantages are poorly understood. Genetic recombination produced by sexual reproduction strongly influences evolutionary rates, genome structure, and adaptation, however little is known about how genes and ecosystems interact to maintain sexual reproduction and determine its frequency. In many species, mutations or hybridization give rise to populations that reproduce asexually. However, most species and nearly all higher-order taxa maintain sexual reproduction, implying that the evolutionary loss of sex eventually leads to extinction. This paradox is particularly striking in species capable of both sexual and asexual reproduction. In these species the majority of reproduction is asexual but environmental cues trigger episodic sexual reproduction. Although sex can be readily lost in these species, both asexual and sexual reproduction are maintained over evolutionary time. Thus asexual/sexual species represent an especially powerful system in which to study the dynamic interaction of asexual and sexual reproduction, environment, and species evolution.Of central importance to understanding the dynamics of sex is the evolution and ecological role of the genes that determine the frequency and prevalence of sexual reproduction in populations. Ultimately, these genes influence genetic diversity, rates of adaptation and speciation, and levels of biocomplexity in ecosystems. Despite their importance, few of these genes have been identified in animals and their evolutionary dynamics remain largely unknown. The objective of the research is to isolate and characterize these genes in rotifers, one of the largest, most successful asexual/sexual groups, and to track the evolution and functional interaction of these genes with the genome and the environment in order to understand how genes and environment interact to regulate sexual reproduction and determine its frequency. The project will employ a combination of biochemical, genetic, and mathematical approaches, including protein purification and functional assays, gene library analysis, and the identification of regulatory pathways by comparing natural and laboratory populations that have lost the capacity to reproduce sexually. The first of three aims in this one-year exploratory project is to complete protein purification of the rotifer sex (i.e., mixis) inducing protein (MIP). The second is to obtain amino acid sequence on both the MIP and the rotifer mate recognition pheromone (MRP) so that we can deduce the nucleotide sequence of the genes. The third aim will be the isolation of the MRP and MIP genes by screening a cDNA genetic library made from a sexually reproducing population of rotifers. Ultimately, these measurements will elucidate the forces maintaining sexual reproduction in life cycles, the dynamics of loss of sexual reproduction in lab and natural populations, the underlying genetic mechanisms of such loss, and establish correlations with environmental variables that may influence these processes. Models will be developed to explain and predict the sex ratio, sex induction threshold, and identify environments where loss of sexual reproduction is expected.The project will provide interdisciplinary research training for a research technician and 2 undergraduates. A library of well characterized rotifer stocks will be maintained and samples distributed upon request. The project will expand a website (jbpc.mbl.edu/wheelbase) to provide a searchable database of genetic libraries, experimental results, and descriptions of techniques. These tools and resources will enable many researchers to incorporate rotifers into comparative genetic studies.