The molecular basis of Mullerian mimicry

蝴蝶物种间的拟态是进化和适应的范例，但其分子遗传学基础从未被研究过。在这里，我们将使用现代基因组技术来识别控制赫利柯乌斯属模仿模式的基因，这是一个著名的进化模型系统。尤其令人震惊的是，我们最近发现，三个赫利柯斯物种使用相同的遗传区域来控制颜色模式的变化。在H.Melpomene和H.Erato这两个物种中，这些都是通过相互模仿进化而来的趋同模式。在第三个物种中，Numata的模式非常不同，模仿了来自不同亚科的Ithomiinae物种。此外，在褐飞虱中，该基因是一个‘超基因’，即控制翅膀模式所有方面的单一基因，并且在种群内是多态的(在同一种群中发现了许多看起来不同的形式一起飞行)。因此，基因组的同一区域以某种方式进化成既控制收敛模式又控制分歧模式。在这里，我们将使用已经在H.Melpomene中开发的标记来识别其他两个物种的感兴趣区域，并获得足够大的区域的DNA序列，我们确信该区域包含所有三个物种的感兴趣基因。这将允许比较这三个物种之间这一区域的基因组组织，并测试基因组重组，这可能是翅膀模式进化的基础。特别值得一提的是，有一种长期存在的假设，即像在Numata中看到的那样，可能会通过逐渐将几个基因移动到一起而产生一个‘超级基因’(这样做的进化优势是在野生种群中避免了不适合的中间模式)。这项研究将允许在分子水平上对这一假设进行首次明确的检验。然后，我们将确定该区域中所有可能的候选基因，并确定哪些基因在发育中的翅膀中表达，以及它们是否显示出与翅膀图案相关的任何图案。因此，我们的目标是鉴定控制黑斑潜蝇后翅上一条带的Yb基因，并比较这三个物种在该基因座区域的基因组组织。这项工作提供了一个不同寻常的机会，将其在自然繁殖中的重要性与DNA序列水平上的变化联系起来。这些结果将有助于未来研究基因的强烈选择如何影响周围基因组的变异。

Mimicry among butterfly species is a paradigm example of evolution and adaptation, but its molecular genetic basis has never been studied. Here we will use modern genomic techniques to identify genes controlling mimicry patterns in the genus Heliconius, a well-known evolutionary model system. What is particularly striking is our recent discovery that three Heliconius species use the same genetic region to control variation in colour patterns. In two of the species, H. melpomene and H. erato, these are convergent patterns that evolved through mutual mimicry. In the third species, H. numata, the patterns are very divergent and mimic species from a different sub-family, the Ithomiinae. Furthermore in H. numata the locus is a 'supergene' i.e. a single locus that controls all aspects of wing pattern and is polymorphic within populations (many different-looking forms are found flying together in the same population). Thus, the same region of the genome has somehow evolved to control both convergent and divergent patterns. Here we will use markers already developed in H. melpomene to identify the region of interest in the other two species and obtain DNA sequence for a sufficiently large region that we are sure contains the gene of interest in all three species. This will allow a comparison of genome organisation in this region between the three species and a test for reorganisation of the genome that may underlie the evoluion of wing pattern. In particular there is a long-standing hypothesis that a 'supergene' such as that seen in H. numata might arise by gradually moving several genes together (the evolutionary advantage of this is that unfit intermediate patterns are avoided in wild populations). This study will allow the first explicit test of this hypothesis at a molecular level. We will then identifiy all the possible genes in this region that are candidates for being the patterning locus, and determine which ones are expressed in developing wings and whether they show any patterns that correlate with the wing patterns. We therefore aim to identify the Yb gene that controls a band on the hindwing of H. melpomene, and compare the organisation of the genome in the region of this locus between the three species. This work offers an unusual opportunity to link a trait whose importance in natural poulations is well studied with a change at the level of DNA sequences. The results will facilitate future studies of how strong selection on a gene affects variation in the surrounding genome.