QUANTITATIVE TRAIT LOCI RELATED TO DROSOPHILA SPECIATION

人们对物种形成的遗传学重新产生了兴趣，产生了许多理论和实证结果。然而，大多数关于物种之间形态/行为差异的多基因的定位研究都有非常粗糙的分辨率，只能降低到非常大的染色体片段的水平。导致这些进化变化的真正基因是未知的。果蝇交配选择的一个特征——雄性梳状体，是进一步研究的理想模式系统。性选择在兄弟物种之间产生了差异，这些差异只表现出部分的合子后分离，从而使遗传分析成为可能。此外，负责性梳形成的生化和发育途径是最容易理解的，有大量的候选基因可供选择。我们的长期目标是剖析种间差异的分子遗传基础，使用性别梳进化作为模型。我们将利用73A-84BD区域，已知该区域贡献了D. simulans和D. mauritiana之间牙齿数量差异的一半。这个区域也影响肛板、钩骨和第5胸骨上的刚毛数。首先，我们将把定位精度提高10倍，以确定这些效应是由具有多效性效应的一个主要基因引起的，还是由具有性状特异性效应的几个基因引起的，还是由具有较小的加性或上位性效应的几个基因引起的。其次，我们将利用P元素跳跃和基于位点特异性P元素诱导的雄性重组的定位来鉴定这些数量性状基因（QTG）。第三，我们将比较导致种内变异的等位基因与导致种间差异的等位基因。我们将抽取100个天然的D. simulans QTG等位基因，并在100-200kbp染色体间隔内将其替换到其他相同的遗传背景中。这将决定天然QTG等位基因效应的分布。我们将确定修饰性梳的QTG等位基因之间的分子多态性，并发现它们在D. simulans和D. mauritiana中的频率。最后，我们将测试这些QTG等位基因是否有助于物种之间的交配前和交配后生殖隔离。这种对几种性状的遗传学的综合评估将进一步加深我们对物种形成遗传学的理解。

There has been renewed interest in the genetics of speciation, yielding many theoretical and empirical results. However, most mapping studies of polygenes responsible for morphological/behavioral differences between species have had very crude resolution, only down to the level of very large chromosome segments. The actual genes responsible for these evolutionary changes are unknown. A trait involved in Drosophila mating choice, male sex comb, is an ideal model system for further progress. Sexual selection has generated differences between sibling species that exhibit only partial postzygotic isolation, enabling genetic analysis. Moreover, the biochemical and developmental pathways responsible for sex comb formation are among the best understood, with a large choice of candidate genes. Our long-term goal is to dissect the molecular genetic basis of interspecific differences using sex comb evolution as a model. We will capitalize on the region 73A-84BD, known to contribute half of the tooth number difference between D. simulans and D. mauritiana. This region also affects bristle number on the anal plate, clasper, and the 5th sternite. First, we will increase the mapping precision ten fold to determine whether these effects are due to on e major gene with pleiotropic effects, several genes with trait-specific effects, or several genes with smaller, additive or epistatic, effects. Second, we will identify these quantitative trait genes (QTG) using P element hopping and mapping based on site-specific P element- induced male recombination. Third, we will compare the alleles contributing to intraspecific variation with those causing interspecific differences. We will sample 100 natural D. simulans QTG alleles and substitute them into the otherwise identical genetic background within 100-200kbp chromosome intervals. This will determine the distribution of effects of natural QTG alleles. We will identify molecular polymorphisms segregating between QTG alleles that modify sex comb, and find their frequencies in both D. simulans and D. mauritiana. Finally, we will test whether these QTG alleles contribute to pre- and postmating reproductive isolation between species. This comprehensive assessment of the genetics of several traits will further our understanding of the genetics of speciation.