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

霍华德9726502十年的研究表明，平地蟋蟀AlLonemobius Fasciatus和A.Socius是通过同种精子优先进行生殖隔离的。换句话说，这两个物种在自然界中产生的杂交后代很少，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佳。这是生物学家清楚地了解将两个密切相关物种生殖隔离的特征的极少数情况之一。这种生殖障碍的遗传控制将通过数量性状基因座(QTL)定位研究来评估。这是一项相对较新的技术，允许生物学家列举和定位控制复杂特征的基因(或QTL)，例如同种精子优先。作图群体将足够大，足以检测到对同种精子优先顺序有微小影响的QTL。因此，这项研究将使人们能够清楚地评估大效应基因和小效应基因在生殖隔离发展中的作用。一旦确定了QTL，将逐一检查每个QTL的影响。通过精心设计的遗传杂交，来自黑曲霉的单个QTL将被引入到黑曲霉中，反之亦然。这样产生的蟋蟀将允许从通常的遗传背景中分离出QTL进行研究，从而直接测试QTL在控制同种精子优先顺序方面的作用。最后，最近的研究表明，同种精子的优先地位进化得很快，可能经常是不同种群之间出现的第一个生殖障碍。因此，重要的是要了解这种障碍如何影响密切相关物种之间的重叠区。同种精子优先顺序对重叠区域的影响将通过遗传和人口模型方法进行分析。物种形成是形成新物种的过程，也是导致地球上生命多样性的过程，生物学家对此知之甚少。这是人类保护物种多样性努力的一个严重缺陷，除非继续产生新的物种，否则不可能取得成功。事实证明，要理解密切相关物种之间生殖障碍的遗传基础尤其困难。这种困难可以归因于两个因素：1)生殖隔离的多面性使得很难识别分离两个物种的特征；2)直到最近，才有必要的工具来剖析复杂的特征。以筋膜亚种和亚种亚种为例，经过十年的艰苦研究，第一个困难被克服了。第二个困难已经被最近的遗传学进步所克服，这些进步导致了几乎可以在任何生物体中绘制图谱的标记的开发。绘制的标记允许监测基因组不同区域对生殖障碍的影响。将目前对阿洛内莫比乌斯系统的理解与遗传学的这些新发展结合起来，将为生殖障碍的遗传学提供前所未有的洞察力。特别是，这项拟议的研究将允许确定筋膜吸虫和社交吸虫之间的生殖隔离是由几个主效基因控制的，还是由许多微效基因控制的。这一区别是一场持续了一个多世纪的辩论的核心，对于理解种群的空间分离对于物种形成是否必要，以及物种形成所需的时间是大是小至关重要。最后，同种精子优先的遗传控制研究归根结底是对生育问题的遗传控制的研究。因此，这项研究提供的对不孕不育的见解将与包括人类在内的许多生物体相关。

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.