The Genetic Control and Evolutionary Significance of a Barrier to Interspecific Hybridization

霍华德9726502 十年来的研究表明，地面蟋蟀，Allonemobius fasciatus和A。socius，是生殖隔离同种精子优先。 换句话说，这两个物种在自然界中很少产生杂交种，因为一个物种的精子在另一个物种的雌性生殖道中运作不良。 这是生物学家对繁殖隔离两个密切相关物种的特征有清楚了解的极少数情况之一。 将通过数量性状基因座（QTL）定位研究评估这种生殖障碍的遗传控制。 这是一项相对较新的技术，允许生物学家计数和定位控制复杂性状的基因（或QTL），如同种精子优先。 作图群体将足够大以检测对同种精子优先有甚至很小影响的QTL。 因此，这项研究将允许一个明确的评估的作用，基因的作用与大的影响和基因的作用与生殖隔离的发展小的影响。 一旦确定了QTL，将在个体基础上检查每个QTL的影响。 通过精心设计的遗传杂交，从A. fasciatus将被引入A. socius和反之亦然。 蟋蟀如此 产生的QTL将允许从其通常的遗传背景中孤立地研究QTL，从而直接测试QTL在控制同种精子优先中的作用。 最后，最近的研究表明，同种精子优先发展迅速，往往是第一个生殖障碍之间出现的分歧群体。 因此，重要的是要了解这种障碍如何影响密切相关的物种之间的重叠区。 将通过遗传和人口统计学建模方法分析同种精子优先对重叠区的影响。 物种形成是新物种形成的过程，也是地球上生命多样性的形成过程，生物学家对这一过程的了解相对较少。 这是人类保护物种多样性努力中的一个严重缺陷，除非新物种继续产生，否则这种努力不可能成功。 对近亲物种之间生殖障碍的遗传基础的理解已经证明， 特别困难。 困难可以归因于两个因素：1）生殖隔离的多方面性质使得很难识别隔离两个物种的特征，2）直到最近才有必要剖析复杂特征的工具。 在A. fasciatus和A.第一个困难是经过十年的艰苦研究克服的。 第二个困难已经克服， 遗传学的进步导致了几乎可以在任何生物体中绘制的标记的发展。 映射标记允许基因组的不同区域对生殖屏障的影响被监测。将目前对Allonemobius系统的理解与遗传学的这些新发展相结合，将为生殖障碍的遗传学提供前所未有的见解。 特别是，拟议的研究将允许确定是否A。fasciatus和A.群聚受少数主效基因或多个效效基因控制。 这种区别是争论的中心，争论已经持续了世纪，对于理解种群的空间分离是否是物种形成所必需的以及物种形成所需的时间是长是短至关重要。 最后，同种精子优先顺序的遗传控制研究归结为 对生育问题的遗传控制的研究。 因此，这项研究提供的对不育的见解将与包括人类在内的许多生物体有关。

Howard 9726502 Ten years of research have demonstrated that the ground crickets, Allonemobius fasciatus and A. socius, are reproductively isolated by conspecific sperm precedence. In other words, the two species produce few hybrids in nature because sperm from one species operates poorly in the reproductive tract of females from the other species. This is one of the very few situations in which biologists have a clear understanding of the trait that reproductively isolates two closely related species. The genetic control of this reproductive barrier will be assessed through a quantitative trait loci (QTL) mapping study. This is a relatively new technique that allows biologists to enumerate and locate the genes (or QTLs) that control a complex trait, such as conspecific sperm precedence. The mapping populations will be large enough to detect QTLs that have even a small effect on conspecific sperm precedence. Thus the study will allow a clear evaluation of the role of genes with large effects and the role of genes with small effects on the development of reproductive isolation. Once QTLs have been identified, the effects of each will be examined on an individual basis. Through carefully designed genetic crosses, single QTLs from A. fasciatus will be introduced into A. socius and vice-versa. The crickets so produced will allow a QTL to be studied in isolation from its usual genetic background, and thereby directly test the role of the QTL in controlling conspecific sperm precedence. Finally, recent studies indicate that conspecific sperm precedence evolves quickly and may often be the first reproductive barrier to arise between diverging populations. Therefore, it is important to understand how such a barrier influences zones of overlap between closely related species. The effect of conspecific sperm precedence on zones of overlap will be analyzed through a genetic and demographic modeling approach. Speciation, the process by which new species are formed and ther efore the process responsible for the diversity of life on earth, is relatively poorly understood by biologists. This is a critical shortcoming in humanity's efforts to preserve species diversity, which cannot succeed unless new species continue to be generated. Reaching an understanding of the genetic basis of reproductive barriers between closely related species has proven particularly difficult. The difficulty can be attributed to two factors: 1) the multi-faceted nature of reproductive isolation makes it hard to identify the traits that isolate two species, and 2) the tools necessary to dissect complex traits were not, until recently, available. In the case of A. fasciatus and A. socius the first difficulty was overcome by ten years of painstaking research. The second difficulty has been overcome by recent advances in genetics that have led to the development of markers that can be mapped in virtually any organism. Mapped markers allow the effects of different regions of the genome on a reproductive barrier to be monitored. Combining the current understanding of the Allonemobius system with these new developments in genetics will provide unprecedented insight into the genetics of reproductive barriers. In particular, the proposed research will allow a determination of whether reproductive isolation between A. fasciatus and A. socius is controlled by a few genes of major effect or by many genes of small effect. This distinction is at the center of a debate that has raged for more than a century and is critical for understanding whether spatial separation of populations is necessary for speciation and whether the time required for speciation is large or small. Finally, the study of the genetic control of conspecific sperm precedence boils down to the study of the genetic control of fertility problems. Thus, the insights into infertility provided by this research will be relevant to many organisms, including humans.