A population genetic approach to speciation in wild tomatoes

在这个跨学科的项目中，在群体遗传学和系统遗传学的界面上，研究了番茄属（野生番茄）的物种形成过程，在全基因组范围内（即在基因组的多个位点上）测量物种内部和物种之间的DNA序列变异。虽然现存的9种番茄在形态上是不同的，但分子证据越来越多地表明这些物种非常年轻。这使得我们可以用群体遗传学的方法来分析交配制度、人口统计学和自然选择对番茄物种起源和分化的影响。特别有趣的是交配系统的作用。尽管种类不多，番茄属却包含了多种多样的交配系统。除了交配制度，人口因素也很重要。为了评估基因流动在番茄早期物种分离后的作用，对数据进行了物种形成模型拟合。这个模型假设一个祖先物种在过去的某个时刻分裂成两个后代物种，在早期物种之间没有进一步的基因流动。提取序列数据中包含的家谱信息（即共享多态性位点、仅在一个分类群中存在多态性位点以及种间固定差异），以估计模型参数，包括种间分化时间。

In this interdisciplinary project at the interface of population genetics and phylogenetics, speciation processes in the genus Lycopersicon (wild tomatoes) are examined measuring DNA sequence variation within and between species at a genome-wide scale (i.e., at multiple loci across the genome). Although the extant nine tomato species are morphologically distinct, molecular evidence is mounting that these species are very young. This allows us to use a population genetic approach to analyze the effect of mating system, demography and natural selection on the origin and divergence of the tomato species. Of particular interest is the role of the mating system. Despite the small number of species, the tomato genus encompasses a great diversit of mating systems. In addition to the mating system, demographic factors are important. In order to assess the role of gene flow between the tomato species following incipient species separation, a speciation model is fitted to the data. This model assumes that an ancestral species split into two descendent species at some point in the past, with no further gene flow between the incipient species. The genealogical information contained in sequence date (i.e., shared polymorphic sites, sites polymorphic in only one of the two taxa, and fixed differences between species) is extracted to yield estimates of the model parameters, including the divergence time between species.