Unlocking the genomics of species formation in Amazonian and high-latitude birds

我的研究调查了为什么与高纬度地区相比，热带地区拥有如此多的物种。一个关键理论将热带的高度丰富与物种形成加速联系在一起，然而，我们对物种形成的生物地理驱动因素以及在生物多样性的热带地区完成物种形成的时间长度的理解仍然处于初级阶段。这项提议的目标是利用基因组数据的力量来确定在地球上物种最丰富的地区-亚马逊盆地-推动鸟类物种形成的生物地理过程，并测试与物种稀缺的加拿大社区相比，那里完成物种形成所需的时间是否更短。众所周知，宽阔的河流是亚马逊大部分地区林下鸟类的有效屏障，是促进亚马逊物种形成的最有可能的生物地理屏障。然而，我们最近的研究表明，在亚马逊外围的源头地区，河流不再是有效的扩散障碍，那里的物种很容易穿过狭窄的河道并进行杂交。然而，在冰川时期，从源头地区撤出的森林和大河可能是推动物种形成的有效障碍。为了验证这一理论，我们的第一组项目将寻找一系列鸟类物种种群规模变化和最近范围扩大到源头区域的预期基因组签名。在被地理屏障隔绝之后，种群开始积累遗传差异，最终导致生殖隔离：无法相互生育成功的后代。生殖隔离标志着物种形成的终点。第二组项目将对整个基因组进行测序，并研究杂交，以测试热带地区与高纬度地区生殖隔离进化的速度。我的实验室将量化物种的基因组如何通过杂交区的杂交来抵抗物种之间的同质化-杂交区是不同物种接触和杂交的地理区域。每个杂交区提供物种形成过程的时间快照，一旦生殖隔离完成，物种之间的基因组同质化就会停止。通过分析进化年龄从几十万年到四百多万年的22个物种对之间的鸟类杂交区域，我们将确定亚马逊地区生殖隔离的时间表是否如预期的那样快，如果快速物种形成推动物种丰富的话。我们还将对加拿大的15对姐妹物种和亚马逊地区的15对高质量的参考基因组进行排序，并比较基因组获得染色体重排的速度。这些重排被认为是导致生殖隔离的重要因素。总而言之，这些大规模的比较项目将使我的实验室能够测试物种形成在亚马逊地区高度物种丰富中所起的作用。

My research investigates why the tropics harbor an extraordinary number of species in comparison with high latitudes. A key theory links high tropical richness to accelerated speciation-the formation of new species-yet our understanding of the biogeographic drivers of speciation and the length of time to complete speciation in biodiverse tropical regions remains rudimentary. The goal of this proposal is to harness the power of genomic data to determine the biogeographic processes that drive avian speciation in the most species-rich region of the planet-the Amazon basin-and to test whether the length of time required to complete speciation is shorter there compared to species-poor communities of Canada. Wide rivers are known to be effective barriers for understory birds over much of Amazonia and represent the most probable biogeographic barriers promoting Amazonian speciation. Yet our recent work demonstrated rivers cease to be effective dispersal barriers in headwater regions of the Amazon periphery, where species readily cross narrow river channels and hybridize. However, during glacial periods forests retracted out of headwater regions and large rivers may have been effective barriers driving speciation. To test this theory, our first set of projects will look for the expected genomic signatures of changes in population size and recent range expansion into headwater regions across a series of avian species. Following their isolation by geographic barriers, populations begin to accumulate genetic differences, culminating in reproductive isolation: the inability to produce successful offspring with each other. Reproductive isolation marks the endpoint of speciation. The second set of projects will sequence whole genomes and study hybridization to test the evolutionary speed at which reproductive isolation evolves in tropical versus high-latitude regions. My lab will quantify how species' genomes resist becoming homogenized between species through interbreeding at hybrid zones-geographic regions where diverging species come into contact and interbreed. Each hybrid zone provides a snapshot in time of the speciation process, with cessation of genomic homogenization between species occurring once reproductive isolation is complete. By analysing avian hybrid zones between 22 species pairs, varying from a few hundred thousand to over four million years in evolutionary age, we will determine whether the timeline to reproductive isolation is faster in Amazonia, as expected if rapid speciation drove high species richness. We will also sequence high-quality reference genomes for 15 pairs of sister species in Canada and 15 in the Amazon and compare rates at which genomes acquire chromosomal rearrangements. These rearrangements have been implicated as important in generating reproductive isolation. Together, these large-scale comparative projects will enable my lab to test the role of speciation in contributing to the Amazon's high species richness.