Genetics of Postzygotic Isolation: The Extent of Genomic Coadaptation in Populations of a Microcrustacean

[0077940]种群间的杂交在某些情况下会增加适合度（杂种活力），而在另一些情况下会降低适合度（远交抑制）。远交抑制是一个值得关注的保护问题，对物种形成的研究也很重要，因为它标志着合子后分离的最早阶段。提出的工作将利用加利福尼亚虎脚类动物探索近亲繁殖抑郁症的遗传基础。这个物种非常适合这样的研究，因为它的世代时间短，易于饲养和显著的种群结构，生殖相容的种群范围从遗传上难以区分到线粒体DNA差异超过20%。近亲繁殖的衰退在这个物种中有很好的记录。提出的研究包括四个目标：1)利用一系列分子标记建立一个连锁图谱。连锁群的确定将有助于加州小蚊雌性缺乏重组。2)寻找加州小蠊的性别决定染色体。这将作为(1)中标记筛选的副产品来完成，并将允许测试性染色体在物种形成中的作用。3)在广泛发散范围内的一系列4个杂交中，检验整个染色体的适合度效应和染色体间的相互作用。这将包括测量回交杂交种的生存能力和基因型之间的关系。结果将评估整个基因组的共同适应程度，并揭示冲突的基因相互作用如何随着时间的推移而积累。4)验证染色体内和染色体间相互作用的适合度效应，并检验物理连锁位点之间更强的共适应的预期模式。结果将对生物学的许多不同领域具有重要意义。通过测量上位性的大小，这些数据将有助于基本的进化理论，这是进化生物学家越来越感兴趣的一个因素。结果将与生殖隔离的机制特别相关，并将与关于果蝇的大量而优雅的工作进行有趣的比较。最后，所提出的工作将有助于保护生物学领域，该领域越来越关注种群间混合的后果。由于共适应基因复合物的性质和程度对近亲繁殖萧条的持续时间有影响，因此本研究可能与管理策略的设计有关。

0077940EdmandsHybridization between populations results in increased fitness (hybrid vigor) in some cases, and decreased fitness (outbreeding depression) in others. Outbreeding depression is a subject of concern for conservation and is also important to the study of speciation, because it marks the earliest stages of postzygotic isolation. The proposed work will explore the genetic basis of outbreeding depression using the copepod Tigriopus californicus. This species is well suited for such a study due to its short generation time, ease of husbandry and remarkable population structure, with reproductively compatible populations that range from genetically indistinguishable up to more than 20% divergent in mitochondrial DNA. Outbreeding depression is well documented in this species. The proposed study includes four objectives:1) To develop a linkage map, using a battery of molecular markers. Linkage group determination will be facilitated by the lack of recombination in T. californicus females.2) To find the sex-determining chromosome in T. californicus. This will be accomplished as a byproduct of the screening of markers in (1) and will allow tests of the role of sex chromosomes in speciation.3) To test fitness effects of whole chromosomes and interactions between chromosomes in a series of four crosses spanning a wide range of divergence. This will involve measuring associations between viability and genotype in backcrossed hybrids. Results will assess the extent of coadaptation across the entire genome and will reveal how conflicting gene interactions accumulate over time. 4) To demonstrate the fitness effects of interactions both within and between chromosomes and to test the expected pattern of stronger coadaptation between physically linked loci. Results will have significance for a number of different fields of biology. The data will contribute to basic evolutionary theory by measuring the magnitude of epistasis, a factor of increasing interest to evolutionary biologists. Results will be particularly relevant to the mechanics of reproductive isolation and will allow interesting comparisons to the large and elegant body of work on Drosophila. Finally, the proposed work will contribute to the field of conservation biology, which is becoming increasingly concerned over the consequences of interpopulation mixing. Because the nature and extent of coadapted gene complexes has implications for the duration of outbreeding depression, this research may be relevant to the design of management strategies.