Female limited Batesian mimicry: epistasis and the path to perfection

非洲模仿燕尾凤蝶（Papilio dardanus）是贝叶斯模仿最原始、最具代表性的例子之一。该物种展示了十几种不同的雌性颜色形式，它们都由一个被称为h的遗传位点控制，有趣的问题是，这些不同的形态是如何在达达努斯p.d erdanus的进化史上获得的，因为模仿者必须离开由保护性表型提供的适应高峰，以达到另一个提供同等甚至更好保护的位置。迄今为止大部分未经证实的“超基因”假设可以解释H位点的复杂影响。此外，超基因假说提出了一个两步进化模型，其中“大效应”突变与一个新模型提供了普遍的相似性，该模型随后被所谓的“修饰者”改进。提出的研究是试图测试这个模型，从而了解形态多样性是如何在自然界中产生的。我最近对H位点的分子表征揭示了基因组相应区域真正令人兴奋的事实，并暗示了一种可能的机制。我发现，编码转录因子的两个非常相似的基因，嵌入的和嵌入的，位于H位点，特定的等位基因在遗传上与特定的形态完全相关。这将在分子水平上解决氢的同一性问题，但不能解决它的功能问题。为了产生巨大的形态多样性，H基因产物必须与上游和/或下游成分的信号级联相互作用。这些组件是什么，它们在不同的变体之间有什么不同？观察到的差异是否证实了假设的修饰语是渐进进化的一种手段（正如达尔文提出的，但没有证明进化的大步骤可能更合理）？这项研究将使用最新的DNA技术来解决这些问题。首先，使用DNA足迹技术，我将研究嵌入/嵌入区域是如何被调节的，即哪些转录因子与它结合以及确切的位置？这些足迹在不同的变体之间是否不同，如果是的话，这种机制的含义是什么？其次，我将研究哪些基因是由嵌入/嵌入的转录因子控制的，再次寻找变体之间的差异。第三，通过绘制潜在修饰因子，采用遗传方法来了解H控制的信号级联的组成部分。最后，由于多态性仅限于雌性，而雄性具有非常不同的外观，因此形态的规范也必须与性别决定有关。这是一个特别有趣的方面，将通过分别评估男性和女性（也包括与男性相似的“男性样女性”）的基因表达实验来研究。该研究将解决以下问题：形态进化的主要步骤是如何在基因组中表现出来的，它们与形态（或其他性状）变异的关系如何，以及这些变化在多大程度上是由于网络相互作用的复杂性，而不是特定位点的变化。

The African Mocker Swallowtail Papilio dardanus is one of the original, and most iconic, examples of Batesian mimicry. The species exhibits more than a dozen different female colour forms all controlled by a single genetic locus, which has been termed H. Intriguing is the problem of how these diverse morphs were acquired in the evolutionary history of P. dardanus, as mimics have to leave the adaptive peak provided by a protective phenotype to reach another position providing equal or even better protection. Hitherto largely unproven postulates of a 'supergene' could explain the complex effects of the H locus. In addition, the supergene hypothesis proposed a two-step model of evolution, by which 'large-effect' mutations provide general resemblance with a novel model, which is subsequently refined by so-called 'modifiers'. The proposed study is an attempt to test this model and hence to understand how morphological diversity is generated in nature. My recent molecular characterisation of the H locus has revealed truly exciting facts about the corresponding region of the genome and hints at a possible mechanism. I have found that two closely similar genes, engrailed and invected, coding for transcription factors, are located at H and specific alleles are genetically fully associated with particular morphs. This would solve the question about the identity of H on a molecular level, but not its function. In order to produce the great morphological diversity, the H gene products have to interact with a signalling cascade of upstream and/or downstream components. What are these components, and how do they differ among morphs? Do the observed differences corroborate the hypothesized modifiers as a means of gradual evolution (as proposed by Darwin but not proven where evolutionary large steps may be more plausible)? This study will use latest DNA technology to resolve these questions. First, using DNA footprinting techniques I will investigate how the engrailed/invected region is regulated, i.e. which transcription factors bind to it and where exactly? Do these footprints differ among morphs, and if so, what are the implications for the mechanism? Second, I will investigate what genes are controlled by the engrailed/invected transcription factors, again searching for differences among the morphs. Third, a genetic approach is used to understand the components of the H controlled signalling cascade, by mapping potential modifiers. Finally, as the polymorphism is limited to the females, while males have a very different appearance, the specification of the morphs also has to link to sex determination. This is a particularly intriguing aspect which will be studied by assessing the described gene expression experiments separately in males and females (and also including 'male-like females' which resemble the males). The study will resolve the question about how major steps in morphological evolution are manifest in the genome, how they relate to morphological (or other trait) variation, and to what degree these changes are due to complexity of network interactions, rather than changes in particular loci.