Testing mechanisms of speciation and hybridization in terrestrial vertebrates

有大量的证据表明物种形成的过程，即一个物种进化成两个物种，但通常推动这一过程的力量是有争议的。一些人提出物种间生殖隔离的进化是由对不同栖息地的适应所驱动的。另一些人则提出，生殖隔离是物种内部不断变化的性选择的结果，导致它们在接触时不相容。我们将通过比较加拿大西部和西伯利亚中部不同物种对的性状分化和生殖隔离模式来检验这些观点。这两个地区在冰河时期都没有森林。现在，每一个都包含许多不同的西部和东部鸟类之间的接触区，这些鸟类在不同的避难所中分化。这些接触区为研究新物种如何产生提供了一个“天然实验室”。我们的目标是研究这些地区的多物种对是否以及如何形成生殖隔离，然后得出关于促进或阻碍物种形成的因素的一般性结论。我们将研究遗传、歌曲、生态、迁徙行为、体型和大小的地理差异，以测量生殖隔离及其原因。除了帮助解决物种形成中性选择和自然选择的相对重要性外，这些研究还将检验(1)杂交和(2)季节迁徙行为在物种形成中的重要性。为了检验杂交，我们将比较三个莺的杂交区，并确定在选择中是否存在基因组的共同部分。我们还将测试奥杜邦莺是否是已知的鸟类杂交物种形成的第一个案例；初步数据表明确实如此。为了研究季节性迁徙行为，我们将研究两种形式的斯温森画眉在杂交区里迁徙行为的变化；我们假设，纯形式将有不同的迁徙路线，而杂交将有中间路线，并将遭受更高的死亡率。在鸟类中有许多已知的迁徙分界线，我们的研究将是第一个直接测试杂交被选择是因为迁徙行为较差的观点。

There is abundant evidence for the process of speciation, whereby a single species evolves into two, but the forces that usually drive this process are controversial. Some propose that the evolution of reproductive isolation between species is driven by adaptation to differing habitats. Others propose that reproductive isolation evolves as a result of sexual selection driving continual change within species, resulting in incompatibilities when they come into contact. We will test these ideas by comparing patterns of trait divergence and reproductive isolation in a variety of species pairs in western Canada and central Siberia. Both regions were not forested during the Ice Ages. Now, each contains many contact zones between distinct western and eastern forms of birds that diverged in separate refugia. These contact zones provide a 'natural laboratory' for the study of how new species arise. Our goal is to study whether and how reproductive isolation is developing in multiple species pairs in these regions, and then to draw general conclusions regarding the factors that promote or hinder speciation. We will study geographic variation in genetics, songs, ecology, migratory behavior, and body shape and size with the goal of measuring reproductive isolation and its causes. In addition to helping resolve the relative importance of sexual and natural selection in speciation, these studies will examine the importance of (1) hybridization and (2) seasonal migratory behavior in speciation. To examine hybridization, we will compare three warbler hybrid zones and determine whether there are common parts of the genome under selection. We will also test whether the Audubon's warbler is the first known case of hybrid speciation in birds; preliminary data suggest it is. To examine seasonal migratory behavior, we will study variation in migratory behavior across a hybrid zone between two forms of Swainson's thrush; we hypothesize that the pure forms will have divergent migratory routes, while the hybrids will have intermediate routes and will suffer higher mortality. There are many migratory divides known in birds, and our study will be the first to directly test the idea that hybrids are selected against because of inferior migratory behaviors.