Adaptive phenotypes and the barrier to introgression between ecotypes

尽管距达尔文的名著已经过去了150多年，但关于新物种的起源仍有很多需要了解的地方。这个问题从根本上说是一个遗传学问题，因为物种的特点是无法与其他物种交换基因。这种‘生殖隔离’可能是因为偶然的变化降低了杂交后代的适合度，或者是因为适应了不同的环境，或者是因为栖息地选择和交配行为的变化阻止了物种的杂交。一般来说，不知道哪种类型的生殖隔离最先出现，也不知道不同类型的生殖隔离是如何结合在一起产生完全隔离的物种的。在这个项目中，我们打算研究两种形式的蜗牛，一种生活在岩石海岸的蜗牛。一种适应于没有螃蟹捕食者的暴露在海浪中的环境(W)，另一种适应于有任何螃蟹的遮蔽环境(C)。在这些环境相遇的地方，不同的类型可以杂交，尽管它们更喜欢与自己的类型交配。在瑞典海岸，这两种类型之间有许多接触点，我们可以将其用作复制。在每一次接触中，我们将检查Winkles的基因组中的遗传标记。对于基因组的某些部分，我们预计在环境边界附近会看到急剧的变化。这些地区正在经历部分的生殖隔离。对于基因组的其他部分，我们预计变化很小或没有变化，因为它们与任何与生殖隔离有关的特征都没有关联。比较多个接触者给了我们一个非常有效的方法来找到基因组中经历最强生殖隔离的部分。下一个问题是为什么这些区域中的每一个都经历了生殖隔离。为了回答这个问题，我们将确定我们从基因上研究的每一种皱纹的几个重要特征。这些特征包括贝壳的大小和形状，以及蜗牛的“大胆”(它愿意脱壳)。这些角色都与适应波浪暴露和适应螃蟹捕食之间的权衡有关。我们还将测量雄性对不同大小雌性的偏好以及雌性的生殖成功(胚胎数量和发育)。然后，我们可以测试经历隔离的区域中的基因是否会导致这些重要特征的变异，因此生殖隔离是否主要是由于适应、后代的健康或配偶选择。有些区域可能与这些特征中的任何一个都没有关联，这些将是非常有趣的，指出了我们迄今尚未研究的隔离形式。这将是发现基因组隔离区域并解释隔离来源的首批研究之一。因此，这将使我们离解开达尔文关于物种起源的“奥秘之谜”又近了一步。

Even though is is now more than 150 years since Darwin's famous book, there is still much to learn about the origin of new species. The problem is fundamentally one of genetics because species are characterised by their inability to exchange genes with other species. This 'reproductive isolation' can be due to chance changes that reduce the fitness of hybrid offspring, to adaptation to different environments or to changes in habitat choice and mating behaviour that prevent the species from interbreeding. In general, it is not known which type of reproductive isolation appears first or how the different types come together to produce completely isolated species. In this project, we propose to study two forms of winkle, a type of snail that lives on rocky coasts. One form is adapted to wave-exposed environments without crab predators (W) and the other to sheltered environments with any crabs (C). Where these environments meet, the different types can interbreed although they prefer to mate with their own type. On the Swedish coast there are many contact points between the two types which we can use as replicates. In each contact, we will examine genetic markers throughout the winkles' genomes. For some parts of the genome, we expect to see sharp changes close to the environmental boundary. These regions are experiencing partial reproductive isolation. For other parts of the genome, we expect to see little or no change because they are not connected to any traits involved in reproductive isolation. Comparing mutliple contacts gives us a very powerful way to find the parts of the genome that experience the strongest reproductive isolation.The next question will be why each of these regions experiences reproductive isolation. To answer this question, we will determine several important characteristics of each winkle that we study genetically. The characteristics include shell size and shape, and the 'boldness' of the snail (its willingness to come out of its shell). The characters are all associated with a trade-off between adaptation to wave exposure and adaptation to crab predation. We will also measure the preference of males for different sized females and the reproductive success of females (number and development of embryos). We can then test whether genes in the regions that experience isolation contribute to variation in these important traits and so whether reproductive isolation is due mainly to adaptation, to offspring fitness or to mate choice. Some regions may not be associated with any of these traits and these will be very interesting, pointing to forms of isolation that we have not studied to date.This will be one of the first studies to find isolated regions of the genome and to explain the sources of isolation. Therefore, it will take us a step closer to solving Darwin's 'mystery of mysteries', the origin of species.